Science analogies

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This page discusses the nature of analogy and its use in communicating science, and then offers examples of a wide range of analogies for science concepts from sources such as the writings of scientists, popular science books and science journalism.

(I am aware the page has become unwieldy, and I am considering a restructuring to make its use more manageable – please bear with me in the meantime.)

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Analogy

An analogy is a comparison between two things that shows how they are in some sense structurally similar. The analogue (the thing that something of interest is said to be like) is said to map onto the target (the thing of focal interest).

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Some ways in which it might be said 'the atom is like a tiny solar system'.

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For example, the figure above shows how some aspects of a simple atomic are similar to the solar system (as in the common trope that 'an atom is like a tiny solar system'). This comparisons is problematic in some ways (Taber, 2013), but is simply used here to illustrate one way of mapping in an analogy. In effect, this figure comprises of two parallel concept maps which have been set out to show which features of the two systems are supposed to map across.

Read about concept maps

Some other examples of analogies presented in this form and discussed on this site are included among the images in the slide show below:

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Analogies are similar in some ways to similes, which point out that one thing is like another. However, analogy goes beyond simile by explaining (or justifying) the comparison. (Metaphors are similar to similes, except the comparison is made in a implicit way, by suggesting X is Y. See the note at the foot of this page.)

Read about science similes

Read about science metaphors

Analogies can be used as thinking tools and also for communicating ideas to others. In teaching, comparisons such as similes and analogies may be used as one way to 'make the unfamiliar familiar'.

Read more about 'Making the unfamiliar familiar'

For example, it is known that circuit electricity is a difficult topic for many secondary age students, so often analogies are used with more familiar or more easily imagined systems, as a way of helping students conceptualise electricity. (This approach was used in the epiSTEMe project to develop a teaching module for 11-12 year olds.)

Read about 'the epiSTEMe project – electricity module'

An simile that has commonly been used in teaching about atomic structure is that 'the atom is like a tiny solar system'. This becomes  an analogy once the comparison is explained by drawing parallels between the two systems. Such teaching analogies usually have both positive and negative features (positive analogy – things that map, and negative analogy – things that do not map across), and in teaching it is important to success both so that students do not inadvertently make inappropriate mappings. (In one study more students suggested the force attracting the electrons to the nucleus in an atom was gravitational than suggested it was electrical!)

Read about a research paper on 'Upper Secondary Students' Understanding of the Basic Physical Interactions in Analogous Atomic and Solar Systems'

It has been suggested that learners may cope better with the plurality of models they meet in science (for example the progression of models about atomic structure, with shells giving way to orbitals; or the shift in how oxidation or acid may be understood) if they are asked to consider the concepts and models they have been taught as components of a toolbox where they might have to choose a different tool for a different task.

Read the article about 'An Analogy For Discussing Progression in Learning Chemistry'

Analogies are also used in explaining scientific ideas in popular science books and in the news and other media.

Read about 'Science in public discourse and the media'

However analogies have also been used in the processes of science itself, where scientists develop their own thinking, and explain their ideas in their scientific research publications. Scientific analogies can be seen as a kind of model, where considering the phenomenon of interest as being analogous to some other system can be seen as a conjecture – an idea to be tested.

Examples of analogies:

Chirality of molecules:

• molecules can be like gloves or socks: not only molecules, but also ordinary objects can be described as chiral or achiral. For example, gloves are chiral, but socks are achiral (Serendipity. Accidental discoveries in science)

Chemical substances

• Trace elements are like seasoning added to food (Allison Britt, Geoscience Australia)

Infectious disease

• COVID is like a fire (Prof. Andrew Hayward, UCL)

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The following examples are discussed elsewhere on the site (follow the links):

The nucleus as the brain of the cell (Bert in Y10)

A duster and matchboxes used to explain spectroscopy (a teacher analogy reported by Amy, college student)

Scaffolding learning as akin to enzymatic catalysis (using catalysis as a comparison to explain 'scaffolding' of learning)

Perceiving and remembering are like palaeontology (a text book analogy to explain cognitive processes)

A black hole with a magnetic field is like a shaggy dog (science news item)

A faecal transplant is like wild flower seeds in some soil (an analogy used in a radio science programme/podcast)

Medical screening is like job-shortlisting (an analogy used in a public science talk / podcast)

Viral infection triggering an immune response is like igniting a fire (an analogy used by a scientist interviewed for the radio)

Effect of a plant toxin is like the valves of a car's engine being stuck open (example from a scientist's blog)

NASA's solar probe entering the Sun's corona is like putting your hand in the oven (analogy used by NASA scientist in media interview)

Working memory is a bit like triglyceride structure (an analogy for explaining 'chunking' to science teachers?)

A well-planned curriculum is like an enzyme (an analogy for thinking about curriculum structure)

Animals and plants are like two different types of engine (a historical analogy)

A synchrotron is like a race track (scientist's comparison used in a public talk)

Photosynthesis as an analogy for the COVID-19 pandemic (used by an academic explaining his work on ther social impacts of the pandemic)

The brain's reward pathway is like a teeter-totter (see-saw) (used by an academic and clinician work on addition)

Popping corn is like radioactive decay (a teaching analogy)

Stars are like trees in a forest, in that you can infer life cycles from observing them at one time (Prof. Martin Rees, Astronomer Royal, talking on the radio – compare with the Herschel analogy below)

A molecular chain reaction is like a Newton's cradle (analogy used to report a scientific study)

An atomic nucleus may behave like a liquid droplet that divides into two smaller droplets (Meitner & Frisch propose nuclear fission in the scientific literature)

The structure of buckminsterfullerene is like a football (Kroto and colleagues report the discovery of a new allotrope of the element carbon)

Mea culpa

And as a teacher, it almost becomes instinctive to use them!

Determining redshift by spectroscopy is a bit like identifying a fingerprint on a balloon that has been stretched.

Nuclear fusion is like cooking rice in that mass may appear to not be conserved.

Children next to a garden fence as an analogy for the photoelectric effect threshold

Learning from one's own teaching analogy: using an analogy from biochemistry to explain what can go wrong in teaching

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Some examples from writing about science:

Commonly some unfamiliar scientific idea is introduced by being compared to something considered familiar from everyday experience. However when scientists write about their work they also often make comparisons with existing scientific concepts (either from within the same scientific discipline, or across sciences) they assume will be familiar to their readership. I have therefore separated out these two types of comparison:

Analogies with familiar analogues from everyday life – in scientific/scholarly works

Topic	analogy	source of analogy
anatomy	"In the sixteenth century, [network] originally applied to woven goods with a structure formed by intersecting lines. By the next century, anatomists began analogising from these craft goods to the structures of the body. Networks were wet before they were mechanical."	Michael Pettit {historian of the human sciences}
animal's Unwelt	"Every subject spins out, like the spider's threads, its relations to certain qualities of things and weaves them into a solid web, which carries its existence."	Jakob von Uexküll {1864 – 1944, biologist}
atomic structure	"When Rutherford (following Nagoka) conceived of the atom as a miniature solar system – electrons circling the nucleus as planets circle the sun – some philosophers suggested that electrons might really be planets with mountains, oceans and even living creatures."	Norwood Russell Hanson {1924 – 1967, philosopher of science}
atoms	"…it is due to the fact that an unelectrified [neutral] atom is so elusive that unless more than a million million are present we have no means sufficiently sensitive to detect them, or, to put it in another way, unless we had a better test for a man than we have for an unelectrified molecule, we should be unable to find out that the earth was inhabited."	J. J. Thomson {physicist}
black box (phenomenological) theories	"The black box resembles the annual report that the company manager submits to the shareholders: both the theory and the report speak about incomes and outcomes, net gains and net losses, and even of overall-trends; but they do not explain the processes at work (in the company or in the box)."	Mario Bunge {physicist and philosopher of science}
calculus	"…in the invention of the method of fluxions, or, as it is now more generally called, the differential calculus, [Isaac Newton's genius] has supplied a means of discovery, bearing the same proportion to the methods previously in use, that the steam-engine does to the mechanical powers employed before its invention."	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
colour of light	"…Transmutations made by the convening of divers[e] colours are not real; for when the difform Rays are again severed [separated], they will exhibit the very same colours, which they did before they entered the composition; as you see, Blew and Yellow powders, when finely mixed, appear to the naked eye Green, and yet the colours of the Component corpuscles are not thereby really transmuted, but only blended. For, when viewed with a good Microscope, they still appear Blew and Yellow interspersedly."	Isaac Newton
conceptual structure	"An adherent of the theory of abstraction or induction might call our layers [of the conceptual system] 'degrees of abstraction': but I do not consider it justifiable to veil the logical independence of the concept from the sense experiences. The relation is not analogous to that of soup to beef but rather of check number to overcoat."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
cosmology	"To know the height of the mainmast does not suffice for calculating the age of the captain. When you have measured every bit of wood in the ship you will have many equations, but you will know his age no better. All your measurements bearing only on your bits of wood can reveal to you nothing except concerning these bits of wood. Just so your experiments, however numerous they may be, bearing only on the relations of bodies to one another, will reveal to us nothing about the mutual relations of the various parts of space."	Henri Poincaré {1854 -1912, mathematician, physicist and philosopher}
coordination of organs	"If an external organ harbours a complete reflex arc, one can properly call this a 'reflex person'. Sea urchins have a great number of such reflex persons which perform their reflex tasks without central direction, each on its own….Although many reflex persons act together, they work completely independently of one another….One can therefore speak of a 'reflex republic' in which, in spite of the complete autonomy of all reflex persons, a total civil peace reigns, for the tender suction feet of the sea urchin are never fallen upon by the biting, rasping pincers, which would otherwise grab any other approaching object."	Jakob von Uexküll {1864 – 1944, biologist}
dialogue	"If the individual may be compared to a soccer player and the thought collective [e.g. group of scientists engaged in dialogue] to the soccer team trained for cooperation, the cognition would be the progress of the game. Can an adequate report of this progress be made by examining the individual kicks one by one? The whole game would lose its meaning completely."	Ludwik Fleck {1896 – 1961, biologist}
Doppler effect	"To give an intuitive understanding of the Doppler effect, assume we have a swimmer moving away from the shore, so that the waves seem to reach him more quickly. More precisely, their apparent frequency (apparent, since the frequency with which they break on the beach remains constant) increases. As he returns to the shore, he moves in a sense with the waves, so that their apparent frequency is reduced. If we assume that there is in the sea a fixed source of waves (the action of the wind against the current on the water surface), it is the speed of the swimmer in relation to this source that determines the change of frequency."	Hubert Krivine, {physicist}
evolution	"The tree of life is a venerable mode of representation of our knowledge about life, its origins and development. Life starts at the root, the single-celled protoplasm, and then claws its way up the tree until it pinnacles at Homer Simpson."	Geoffrey C. Bowker (Professor of Informatics)
experiment	"Experiment, by enriching the set of naturally occurring facts, is apt to disclose deep and unsuspected aspects of things – as when a friend is asked to risk something."	Mario Bunge {physicist and philosopher of science}
genes	"The genes are arranged in the chromosomes in linear series, roughly comparable to a string of pearls."	Ludwig von Bertalanffy
genetic 'code'	"…nowhere in the natural world is the linguistic character of specification more clearly in evidence than in the genetic code of an organism, which as I have noted before, constitutes a text recorded in a four letter alphabet. The genetic code is thus a written text imprinted on DNA."	Wolfgang Smith {mathematician, physicist, philosopher of science}
geology	"the Under-ground World is a well fram'd House, with distinct rooms, Cellars, and Store-Houses, by great Art and Wisdom fitted together; and not, as many think, a confused and jumbled heap or Chaos of things, as it were, of Stones, Bricks, Wood, and other Materials, as the rubbish of a decayed House, or an House not yet Made."	Athanasius Kircher {1602 – 1680, polymath}
gravitation	"By this formulation one reduced the whole mechanics of gravitation to the solution of a single system of covariant partial differential equations. … But it is similar to a building, one wing of which is made of fine marble (left part of the equation), but the other wing of which is built of low-grade wood (right side of equation)."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
holistic nature of organisms	…the acorn forms numerous buds, from every one of which emerges an organ subject…All organ subjects with their organ melodies join together to form the symphony of the organism of the oak…The process of heightened subjectification of the cell tone to organ melody to organism symphony stands in direct contradiction to any mechanical process that represents the effect of one object on another object. … As in the composition of a duet, the two voices have to be composed for each other note for note, point for point, the meaning factors in Nature stand in a contrapunctual relation to the meaning utilisers."	Jakob von Uexküll {1864 – 1944, biologist}
hypotheses	"The problem 'Which comes first, the hypothesis (H) or the observation (O)?' is soluble; as is the problem, 'Which comes first, the hen (H) or the egg (O)?'. The reply to the latter is , 'An earlier kind of egg'; to the former, 'An earlier kind of hypothesis'."	Mario Bunge{physicist and philosopher of science}
hypotheses	"Once the concept of intelligibility has been thus quantitated and elucidated at the same time, it is rather easy to construct a hypothesis concerning the intelligibly of a message after a certain number of repetitions: the mathematical theory of probability acts as a nest for the hatching of the factual hypothesis. Similarly the theoretical biologist will use physical theories for the formation of biological hypotheses and the historian may use sociological theories for the formation of historical hypotheses. This procedure, of letting a theory of a different species do the work of hatching a hypotheses, may be termed the cuckoo technique. …Scientific hypotheses are not legitimate or illegitimate on account of their origin but in the strength of their tests, both empirical and theoretical: they are given test certificates rather than birth certificates."	Mario Bunge {physicist and philosopher of science}
hypotheses outside of theories	"A heap of uncoordinated hypotheses, though better than no hypothesis at all, may be likened to a huge mass of protoplasm without a nervous system."	Mario Bunge {physicist and philosopher of science}
immune response	"Bordet said that just because twice as much serum is needed to combine with two as with one dose of bacterial emulsion, some bacteriologists argue that antigen and antibody must combine according to a law of definite proportions. That, he said scornfully, was like claiming that paint must react in definite proportions with a wall."	Jules Bordet {1870-1961}, immunologist, Nobel laureate: quoted by Pauline M. H. Mazumdar
infection	"The concept of infectious disease. This is based on the notion of the organism as a closed unit and of the hostile causative agents invading it. The causative agent produces a bad effect (attack). The organism responds with a reaction (defence). This results in a conflict, which is taken to be the essence of disease. The whole of immunology is permeated with such primitive images of war. … It is very doubtful whether an invasion in the old sense is possible, involving as it does an interference by completely foreign organisms in natural conditions. A completely foreign organism could find no receptors capable of reactions and thus could not generate a biological process. It is therefore better to speak of a complicated revolution within the complex life unit than of an invasion of it."	Ludwik Fleck {1896 – 1961, biologist}
infectious disease	"The phthisical soldier is to his messmates what the glandered horse is to its yoke fellow"	Jean-Antoine Villemin {1827 – 1892, physician and medical researcher}
labelling	""Labeling, or name-calling, is a pseudo-explanation and it should be dealt with in an an account of explanation much for the same reason that unauthentic ('false') pearls must be mentioned in a treatise on pearls."	Mario Bunge {physicist and philosopher of science}
language of science	"Some philosophers think that a science is just an artificial language…But that is taking cans for canned food. Science constructs sign systems and works with them but only in so far as they can materialise our ideas concerning nonlinguistic objects, such as chemical binding. Furthermore, science is communicable but it does not serve the purpose of communication….Science, in short, has a language but it not a language…."	Mario Bunge {physicist and philosopher of science}
light	"… Newton … suppose luminous objects actually to dart out from them in all directions, …without ever coming in actual contact with the particles themselves of the bodies on which they fall, but either being turned back and reflected by the repulsive forces before they reach them, or penetrating between their intervals, as a bird may be supposed to fly through the branches of a forest…"	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
materials	"A solid body may be regarded as a fabric, more or less regularly and artificially constructed, in which the materials and the workmanship may be separately considered, and in which, though the latter be ruined and confounded by violence, the former remain unchanged in their nature, though differently arranged."	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
magnetism	"Fludd believed …Magnetic attraction was a "coition or union" between bodies caused by the similarity of their nature. The lodestone, Fludd wrote, "sucketh and attracteth from his center the body of Iron unto it, drawing forth of it his formal beams, as it were his spiritual food."	John Glassie discussing the ideas of Robert Fludd
mass defect	"But if every gramme of material contains this tremendous energy, why did it go so long unnoticed? The answer is simple enough: so long as none of the energy is given off externally, it simply cannot be observed. It is as though a man who is fabulously rich should never spend or give away a cent; no one could tell how rich he was. … Schematically, the process goes like this: An atom of the mass M splits into two atoms of the mass M' and M", which separate with tremendous kinetic energy….The atom M is a rich miser who, during his life, gives away no money (energy). But in his will he bequeaths his fortune to his sons M' and M", on condition that they give to the community a small amount, less than one thousandth of the whole estate (energy or mass). The sons together have somewhat less than the father had (the mass sum M' + M" is somewhat smaller than the mass M of the radioactive atom). But the part given to the community, though relatively small, is still so enormously large (considered as kinetic energy) that it brings with it a great threat of evil."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
mass defect in chemical reactions	"…mass is physically (objectively) nonadditive though empirically additive- much as all Eskimos look the same to unexperienced Europeans."	Mario Bunge {physicist and philosopher of science}
mating behaviour	"…brown ground beetles…go hunting male and female together, but then connect sexually. Once the coupling is consummated, the behaviour of the males towards the females does not change at all, but the latter throw themselves on the males ravenously and tear them limb from limb, against which the males only defend themselves feebly. In the female's environment, the carrier of meaning 'friend' has changed to 'food' without changing its constitution in the least, just as when the curbstone, without changing, gives up its meaning as an element of the path in order to transform itself into a projectile when the mood of the subject 'human being' changes and impresses a different meaning upon the stone."	Jakob von Uexküll {1864 – 1944, biologist}
maturation of the blood	"…the Arab medical writer Rhazes (al-Razi), who believed that babies were bon with watery blood that had to be transformed into dryer, more adult blood by boiling up, losing its moisture, and throwing its sediment out through the pores in a process analogous to the fermentation of wine."	Abū Bakr al-Rāzī discussed by Margaret Delacy
mechanics	"Thus absolute space, absolute time, geometry itself, are not conditions which impose themselves on mechanics; all these things are no more antecedent to mechanics than the French language is logically antecedent to the verities one expresses in French."	Henri Poincaré {1854 -1912, mathematician, physicist and philosopher}
metals	[Historical example – now considered an alternative conception] "Rightly then in some measure does Aristotle make out the matter of metals to be that exhalation which in continuance thickens in the lodes of certain soils: for the vapours are condensed in places which are less hot than the spot whence they issued, and by help of the nature of the soils and mountains, as in a womb, they are at fitting seasons congealed and changed into metals: but it is not they alone which make ores, but they flow into and enter a more solid material, and so make metals. So when this concreted matter has settled down in more temperate beds, it begins to take shape in those tepid places, just as seed in the warm womb, or as the embryo acquires growth…"	William Gilbert [note the first reference 'as in a womb' would by itself be seen as a simile, but Gilbert then develops the analogy further]
mineralogy	"…Bergmann discovered the general fact, that [minerals] could be cloven or split in such directions as to lay bare their peculiar primitive or fundamental forms, (which lay concealed within them, as the statue might be conceived encrusted in its marble envelope,)…"	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
mutation	"…until recently all mutations were regarded as random just because no constant relation between them and controllable agents had been discovered; to be sure, by means of certain radiation it was possible to experimentally induce mutations but never in a predictable way, because radiation acts very much like bombing."	Mario Bunge {physicist and philosopher of science}
nature of science	"…the experimentalist does not accept the Cartesian philosophy, which is to say he [or she] treats his [or her] apparatus not as a mathematical structure but as a perceivable object. Even as there are said to be 'no atheists in the trenches', so indeed there are no bifurcationists in the laboratory."	Wolfgang Smith {mathematician, physicist, philosopher of science}
Newton's models of the universe	"The stellar universe ought to be a finite island in the infinite ocean of space."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
observations/data	"First, observation by itself poses the problem of building theories and it tests them, but theories are not 'abstracted' or 'inferred' from observation reports – if only because these, the bits of evidence, may not refer to the same things as the theories do, just as a glance may suggest love without being love."	Mario Bunge {physicist and philosopher of science}
origin of scientific problems	"In short, practice is a source – alongside with sheet intellectual curiosity – of scientific problems. But giving birth is not rearing."	Mario Bunge {physicist and philosopher of science}
p-n junction	"The holes giving [current] If are climbing up the hill. The holes that give [current] Ig wander randomly in the n [n-type semiconductor] region until by chance they come to the brow of the hill and slide down." "Any less energetic holes attempting the ascent will slide back." "A hill of any height will urge ahead all holes that stray to its brow."	Alan Holden ('The Nature of Solids')
physical science	"Physics is not a machine that can be taken apart. One cannot test every piece individually and wait until it has stood this sort of testing before putting it in the system. Physical science is a system that must be accepted as a self-contained whole, an organism of which no single part can be made to work without all the others, even those farthest removed, becoming active – some more, some less, but all in some precise degree. When the functioning is blocked in any way the physics must try to guess from the behaviour of the whole which part is at fault and in need of repair, with no possibility of isolating and testing it separately. Given a watch that will not go, the watch maker removes all the parts, examining them one by one until he finds which was out of place or broken, but the physician cannot dissect a patient in order to make a diagnosis; he must guess at the seat and cause of the disease merely by studying a disturbance that affects the whole body. The physicist resembles the latter when he has a defective theory before him which he has to improve."	Ernst Cassirer [Note that in this extract Cassirer makes one analogy whilst rejecting another: the system of physical science is like an organism; but it is not like a machine such as a watch.]
plant anatomy	"The FRUIT-BODY consists of the genitals of plants; thus the FLOWERING is the generation, the ripening of the FRUIT is the birth…Therefore the CALYX is the bedroom, the COROLLA is the curtain, the FILAMENTS are the spermatic vessels, the ANTHERS are the testicles, the POLLEN is the sperm, the STIGMA is the vulva, the STYLE is the vagina, the [VEGETABLE] OVARY is the [animal] ovary, the PERICARP is the fertilised ovary, and the SEED is the egg. The calyx could also be regarded as the lips of the c*nt or the foreskin…The ground is the STOMACH of plants, the root is their VESSELS THAT CARRY CHYLE, the trunk is their BONES, the leaves are their LUNGS, and heat is their HEART; for this reason, a plant was called, by the ancients, an animal turned upside down."	Carl Linnæus {1707 – 1778} (translated by Stephen Freer)
plague	"…if two men went out in the rain both would be 'infected' with the wet, but the dampness did not pass by contagion from one to the other." [i.e., arguing plague was not a contagious disease!]	said to be due to physician to Royalty, Dr John Radcliffe, FRS, reported by historian Margaret Delacy
progress in science	"…[the structure of] modern progressive science … resembles a column of troops on the march. Every discipline, in fact almost every problem, has its own vanguard, the group of research scientists working practically on a given problem. This is followed by the main body, the official community. Then come the somewhat disorganised stragglers. …The vanguard does not occupy a fixed position. It changes its quarters from day to day and even from hour to hour. The main body advances more slowly, changing its stand – often spasmodically – only after years or even decades. Its path does not closely follow that of any one of the vanguards. The main body adjusts its advance according to reports received from the vanguard, but maintains a certain independence. The direction that the main body actually choses from the many suggested by the vanguards is always unpredictable. Paths must first be widened into roads, and the ground levelled, so that the terrain undergoes considerable change before it can become the garrison of the main body."	Ludwik Fleck {1896 – 1961, biologist}
quanta	"Pianistic thinking cannot allow violinistic glissandi: pianos allow a C#, or a D, but nothing in between. Classical physics regarded nature as a complicated violin: that is, differential equations were always in place; but we cannot think of the atom thus. λ depends on the speed of the particle, so a particle in an atomic orbit can only run at certain speeds. It cannot run at intermediate speeds; it cannot exist at intermediate speeds."	Norwood Russell Hanson {1924 – 1967, philosopher of science}
quanta	"Consider the molecule of hydrochloric acid [sic, actually hydrogen chloride], one atom of hydrogen and one atom of chlorine. The hydrogen atom is lighter, and swings around the heavier, near-stationary chlorine atom like a discus in the hand of the spinning athlete. It is as if the athlete could spin only at certain speeds: no faster, no slower, and nothing intermediate."	Norwood Russell Hanson {1924 – 1967, philosopher of science}
quantum formalism	"It is maintained that perhaps the success of the Heisenberg method points to a purely algebraical method of description of nature, that is, to the elimination of continuous functions from physics. The, however, we must also give up, on principle, the space-time continuum. It is conceivable that human ingenuity will some day find methods which will make it possible to proceed along such a path. At the present time, however, such a programme looks like an attempt to breathe in empty space."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
radiation-matter interaction	"Trying to move the ions by that alternating force is like trying to move a child on a swing back and forth by attaching the swing to the clapper of a doorbell. To swing the child, you must alternate your push at a lower frequency ,and to move the ions, you must use light whose frequency is only about 1/100 of the frequency of visible light"	Alan Holden ('The Nature of Solids')
relativity	"… when describing the roles of coordinate systems and frames of reference, [Albert Einstein uses] the curious and confusing analogy of a mollusc (or 'reference mollusc' – his German word bring Bezugsmolluske), indicating that he apparently thought of a coordinate system as a physical thing, swimming around like some soft marine invertebrate which could change its shape with time."	Roger Penrose {physcist and mathematician}
reflexes	Pavlov's "central metaphor – the human nervous system as a central telephone switchboard – illuminated the crucial distinction between unconditional and conditional [conditioned] reflexes. According to Pavlov, inborn unconditional reflexes fixedly tied to a particular response (e.g., the viewing of food) to a specific response (e.g., salivation). Pavlov compared such reflexes to a set of direct, permanent telephone lines. Conditional reflexes (e.g., salivation in response to the ringing of a bell, previously associated with the viewing [p.//p.] of food) could be acquired, lost, and reestablished. Pavlov likened conditional reflexes to flexible temporary connections between telephone users through a switchboard."	Ivan Pavlov (reported by Slava Gerovitch)
relativity	"…I must observe that the theory of relativity resembles a building consisting of two separate stories, the special theory and the general theory. The special theory, on which the general theory rests, applies to all physical phenomena with the exception of gravitation; the general theory provides the law of gravitation and its relations to the other forces of nature."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
research reports	"The summarised report about a field of research always contains only a very small part of the worker's relevant experience, and not even the most important.Missing is that which makes the stylised visual perception of form possible. It is as if the words of a song were published without the tune."	Ludwik Fleck {1896 – 1961, biologist}
science	"The liberty of choice, however, is of a special kind; it is not in any way similar to the liberty of a writer of fiction. Rather, it is similar to that of a man engaged in solving a well-designed word puzzle. He may, it is true, propose any word as the solution; but, there is only one [ital] word which really solves the puzzle in all its parts. It is a matter of faith that nature – as she is perceptible to our five senses – takes the character of such a well-formulated puzzle."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
scientific enquiry	"…having once experienced the advantages which are to be gathered by availing himself [sic] of some of the powers of nature to accomplish his ends, [man] is led thenceforward to regard them all as a treasure placed at his disposal, if he have only the art, the industry, or the good fortune, to penetrate those recesses which conceal them from immediate view. …the investigation of the hidden powers of nature becomes a mine, every vein of which is pregnant with inexhaustible wealth, and whose ramifications appear to extend in all directions wherever human wants or curiosity may lead us to explore."	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
scientific knowledge	"Scientific knowledge is hypothetical to such an extent that some researchers do not realise it (just as a fish may not realise it is immersed in water) and think that there can be a self-contained piece of research that neither presupposes nor involves hypotheses."	Mario Bunge {physicist and philosopher of science}
scientific literature	"The vademecum [handbook] is therefore not simply the result of either a compilation or a collection of various journal contributions. The former is impossible because such papers often contradict each other. The latter does not yield a closed system, which is the goal of vademecum science. A vademecum is built up from individual contributions through selection and orderly arrangement like a mosaic from many coloured stones."	Ludwik Fleck {1896 – 1961, biologist}
scientific research	"Syntheses are beyond infant science just as they are absent from infant thought. Scientific research, just as infant enquiry, starts with questioning but, unlike infant questioning, it culminates with the construction of closely knit systems of ideas, i.e. theories" [Note: Bunge makes ana analogy, then highlights a feature of the 'negative analogy'	Mario Bunge {physicist and philosopher of science}
scientific specialisation	"The area of scientific investigation has been enormously extended, and…it was inevitable that the activity of the individual investigator should be confined to a smaller and smaller section of human knowledge. … A situation is developing similar to the one symbolically represented in the Bible by the story of the tower of Babel."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
scientific theories	"Metaphorically speaking, a scientific theory is like a mollusc with a soft core – the set of high-level hypotheses – surrounded by a somewhat harder but porous shell – the set of low-level or empirical generalizations [sic]…Through the pores of the peripheral part, information about the external world pours in, which enables the central core to produce new particular items (predictions and retrodictions) that are projected to the external world. Sometimes the excreta are more valuable than the food."	Mario Bunge {physicist and philosopher of science}
scientific theories	…infinitely many possible rival theories can yield 'practically the same results'. The technologist, and particularly the technician, are justified in preferring the simplest of them all: in getting things done rather than in gaining a deep understanding of them. For the same reason, deep and accurate theories may be impractical: to use them would be like killing bugs with nuclear bombs. It would be as preposterous – though not nearly as dangerous – as advocating simplicity and efficiency in pure science."	Mario Bunge {physicist and philosopher of science}
senses	"Our sensory organs of the eye, ear, nose, palate, and skin are built according to the principle of a Swedish box of matches [i.e., 'safety' matches], in which the matches only respond to certain effects of the outside world."	Jakob von Uexküll {1864 – 1944, biologist}
solar system	"For us astronomers, [the rings seen around some planets] are the blood spatter on the walls of a crime scene. When we look at the rings of giant planets, it's evidence something catastrophic happened to put that material there"	Prof. Stephen Kane  (Professor of Planetary Astrophysics, University of California, Riverside)
stellar evolution	"This method of viewing the heavens seems to throw them into a new kind of light. They now are seen to resemble a luxuriant garden, which contains the greatest variety of pro­ductions, in different flourishing beds; and one advantage we may at least reap from it is, that we can, as it were, extend the range of our experience to an immense duration. For, to continue the simile I have borrowed from the vegetable kingdom, is it not almost the same thing, whether we live successively to witness the germination, blooming, foliage, fecundity, fading, withering, and corruption of a plant, or whether a vast number of specimens, selected from every stage through which the plant passes in the course of its existence, be brought at once to our view?"	William Herschel {1738 – 1822, composer and astronomer}
temperature	"From the numerical equality of the average kinetic energy of an assembly of molecules and the assembly's temperature [p.//p.] we cannot conclude that 'at bottom' temperature is 'nothing but' s microscopic mechanical property, just as from the interchangeability of 'Plato' and 'Socrates's best disciple' we are not allowed to infer that 'at bottom' Plato was already contained in Socrates."	Mario Bunge {physicist and philosopher of science}
universe	"We might imagine that, as regards geometry, our universe behaves analogously to a surface which is irregularly curved in its individual parts, but which nowhere departs appreciably form a plane something like the rippled surface of a lake."	Albert Einstein {1879 – 1955, theoretical physicist and peace campaigner}
Wassermann reaction (to diagnose syphilis)	"For Wassermann and his co-workers shared a fate in common with Columbus. They were searching for their own 'India' and were convinced they were on the right course, but they unexpectedly discovered a new 'America'. Nor was this all. Their 'voyage' was not straight sailing in a planned direction but an Odyssey with continual change of direction. What they achieved was not even their goal. They wanted evidence for an antigen or an amboceptor, Instead, they fulfilled the ancient wish of the collective: the demonstration of syphilitic blood."	Ludwik Fleck {1896 – 1961, biologist}
wave-particles	"The movement of a wave-packet is thus like an enormous number of dolphins crowding just below a still surface. Their jostling pushesone dolphin above the surface, then another and another, so rapidly and so closely that it might be a single dolphin flashing across the water, according to the laws if classical particle physics… "Outside the packet…there is complete destructive interference of the component waves. (The ocean's surface is unrippled here as the dolphins nullify each other's efforts to break water.)"	Norwood Russell Hanson {1924 – 1967, philosopher of science}

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Analogies with familiar analogues from everyday life – in popular accounts of science

topic	analogy	source of analogy
ad hoc moves	"But this was the ultimate example of a special fix – the predictions of his equations (collapse) didn't match observations (a fairly stable universe). So he just stuck λ in, like duct tape over a leaky pipe."	Matthew Stanley: Einstein's War. How relativity triumphed amid the vicious nationalism of World War 1
anthrax	"PA [protective antigen] is the muscled henchman of the group that attaches to the surface of our macrophages and gathers EF [oedema factor] and LF [lethal factor] to its side. It then slices a slit in the wall of the cell, like a burglar cutting a hole in a glass jewellery case, which allows the other two toxins to penetrate deep inside."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
antibodies	"…antibodies can bind to the surface of bacteria and in a process called 'opsonisation' make consuming the bacterial more appealing to neutrophils, much like sprinkling tiny chocolate chips on a bacterial cookie."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
antibodies	"One way of thinking about the [antibody] heavy chain construction process is imagining you have to make a Mr Potato Head army, and you know that the more variety in your vegetable warriors the better. So you start with picking a head, your constant region, and now you need to give him a pair of eyes (V gene), a mouth (D gene) and a nose (J gene). You put your hand in a bucket with 51 unique sets of eyes and pull out a pair, then you reach into another bucket with 27 different mouths and grab a gob. Then you finally select one of six distinct noses."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
antibodies	"This is tripped by the pollen attaching to the IgE-primed mast cells and, like pulling a pin on a grenade, causing them to unleash their allergy-inducing chemicals."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
antibodies	monoclonal antibodies "are effectively antibodies that act like heat-seeking missiles designed to lock onto a single specific [type of] molecule."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
antigens	""HLA molecules come in different shapes, and some are better able to present certain peptides than others. I like to think of it as an epic dinner service at Downton Abbey, with a plethora of plates, platters, forks and spoons for serving different foods. To be able to serve the full banquet correctly you need a lot of dinnerware. Likewise, the more variety you have in your HLA molecules, the better prepared you are to serve whatever peptides might be squirrelled away inside your cells."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
atomic structure	"Currently, the best models say that there are 172 elements…. 'Element 172 is a chemist's calculation', points out Mark Stoyer. 'But once you reach the massive size of an atom that element 172 would be, the innermost electrons are very relativistic. They gain mass, so are heavier, so the orbit contacts so much those electrons spend a significant fraction of time actually inside the nucleus. Amazing when you think about it – electrons whizzing around inside the nucleus.' Stoyer's right – it would be loosely the equivalent of the Earth orbiting through the Sun."	Kit Chapman, Superheavy. Making and breaking the periodic table
autoimmunity	"There are a range of different things that can tip our tiny but deadly defenders against us. It's a bit like having a paddling pool infested with miniature sharks and dipping your toe in the pool: ordinarily the miniature sharks have no interest in eating toes, and just mill about, perhaps conversing about the weather and gobbling the occasional miniature fish. However, if you've cut your toe and blood gets into the water, all bets are off. The blood-tinged water sets the sharks on a feeding frenzy, where fingers, toes and all other appendages are fair game even if they wouldn't normally be on the shark's dinner menu. There are many environmental factors that can act as blood in our analogy, from obesity, as in Type II diabetes, to perhaps even sunlight levels."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
bacteriophage	"They're like microbial snowflakes, with no two identical…"	Catherine Carver Immune. How your body defends and protects you [Read about this book]
beta decay	"…the trio created the new element 93. It was a vigorous beta radiation emitter, meaning it was likely turning into yet another element. But they had also made something that fizzed with alpha particles instead. Could 93 have beta decayed and given birth to an atomic daughter?"	Kit Chapman, Superheavy. Making and breaking the periodic table
black holes	"They may also have seen, unwittingly, the creation of a black hole, one of those bottomless pits in the sky that seem to be an inescapable consequence of Albert Einstein's theory of gravity."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
bodies	"…the human body is like an exceedingly well-fortified castle, defended by billions of soldiers. Some live for less than a day, others remember battles for years, but all are essential for protecting us. This is the hidden army that we all have inside of us…"	Catherine Carver Immune. How your body defends and protects you [Read about this book]
brain	"In earlier centuries people had believed that thoughts and emotions were carried through the head via hollow tunnels, but now the brain became a series of discrete segments, real estate, if you will, some of its swampy, some of it stately, but all of its perhaps subject to human renovation."	Lauren Slater The Drugs that Changed our Minds
cancer	"Cancer has many faces, none of them pretty and many of them deadly. It wears a mask that conceals its killer features from its would-be assassins – the T cells and Natural Killer cells that roam our bodies. Despite its best attempts to see cancer's true colours, the immune system has a huge challenge on its hands. It's like trying to spot a murderer at the world's biggest masquerade ball where everyone's wearing the same mask, except the homicidal guest's mask has ever so slightly different shaped pieces of glitter around the edges."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
cancer	"…while ordinary cells depend on receiving instructions to multiply, cancer cells are above such things and like malevolent rabbits on a reproductive rampage they replicate at will."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
cancer	"…surely having a hotspot of immune system activity should decrease the chance of cancer's success? It's a bit like recruiting more police only to find your crime rate increases."	Catherine Carver Immune. How your body defends and protects you
cancer	"The white blood cells set about secreting chemicals that promote the growth of cells and the development of new blood vessels. This is normally a great plan when bits of the body have been damaged, but in the case of cancer having these chemicals around is like bringing rocket fuel to a forest fire. These inflammatory chemicals are so beneficial to tumour survival that some tumours don't wait for the immune system to bring fuel to the party – they ooze their own versions of these pro-tumour chemical messengers into their environment."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
candiru	"…the little fish launches itself into the stream of urine and swims up the golden arch and into the narrow opening of the urethra. Once inside it flexes out its spines and, like putting up a large umbrella in a narrow corridor, this lodges it in the shaft of the penis…"	Catherine Carver Immune. How your body defends and protects you [Read about this book]
chemical abundance	"At the time, the best instruments were only sensitive enough to pick up Pu-244 if it made up about 0.1 per cent of a sample. In heavy element terms, that wasn't gold dust: it was a veritable gold mine."	Kit Chapman, Superheavy. Making and breaking the periodic table
chemokines	"The chemokines are the Pied Pipers of the cytokine world, united as a group by their ability to beckon a colourful [sic] array of cells to a particular location. In a process known as chemotaxis, they can call up neutrophils, macrophages and other immune system soldiers to mount a response to injury and infection and begin the healing process."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
chromosome	"One gene occupies one region of a chromosome containing many genes, much like one song occupies one region of a music tape containing many songs overall."	Andrew Scott, Vital Principles. The molecular mechanisms of life
comet formation	"I like to think of the fluffy, icy, dust balls as being almost like the little dust bunnies that exist on the floor of my house when I need to clean. They eventually start to find each other and grow into larger and larger dust bunnies the longer I ignore them. In the solar nebula, the fluffy agglomerates loosely stuck to each other, growing to form larger and larger objects, some of which became the size of present-day comet nuclei, the solid central part of comet. The average comet nucleus is around 10km (6.2 [sic] miles) in diameter, but the largest ones can be up to hundred of kilometres across. There are many much smaller, too: those dust bunnies who never found a mate."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the solar system
comets	"In the theory now prevalent in Cometsville, a comet is a cosmic sorbet: a dirty snowball that comes tumbling out of the freezer of twilight space, far from the sun… If Satan is hurling snowballs at us from the Ooo Cloud, his aim is unimpressive."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comets	"Comets rattled into the archives like aristocrats on the way to the guillotine."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comets	"But the OOpik-Oort Cloud] is a hundred times farther off than that, and as often as once in a million years a star will charge through a segment of it like a wild bull through a garden party, scattering the guests. Perturbed by the star's gravity, many millions of comets take flight, quitting the Solar System for ever. Others change their orbits drastically and they remain in the Cloud. And ten million comets, for the sake of argument, are stopped in their tracks like bull-watchers paralysed with fear."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comets	"The action of a star hurtling thought the Ooo Cloud [Opik-Oort Cloud] can be regarded as a special case of gravitational football, in which comets are booted about the sky. Those that fall into the heart of the Solar System become playthings of the planets, which switch them from orbit to orbit. … In many cases the planets will kick the comets right out of the Solar System, which is the cleanest way of getting rid of them. As the largest planet and chief defender, Jupiter does most of this work, but any of them, the Earth included, will lend a boot now and again. …But the dust disperses continually and is subject to the same kind of gravitational football from the planets as comets are."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comets	"From planetesimals that were probably mainly comets or their remnants, the newborn Earth and its sister planets were subjected to a torrential bombardment compared with which the Vietnam war was a gentle shower."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comets	"One idea on offer in the seventeenth century was … the comet allegedly stirred up the aether in cosmic space like a ship ploughing through the sea."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comets	"And just as a gale blows smoke ahead of a steamship that is travelling down-wind, so the pressure of sunlight carries the more easily visible dust storm ahead of a comet when it is climbing away from the sun."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
comet sampling	"The scientists had to think carefully about what substance they used in the collector to trap the comet particles. A collection material that is too hard would cause the comet particles it encountered to simply bounce straight off, like throwing a tennis ball against a brick wall."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the solar system
comet and asteroid impacts	"Although the rate of impact has slowed considerably since the first few million years of Solar System history – partly because the planets, asteroids and comets gradually settled down into their comfortable orbits – more are still expected to occur in the future. It's Solar System pinball, except we're dealing with lots of balls flying about all at once with a certainty that they will, at some point, collide with other objects in the game."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
comets and asteroids	"For the most part comets and asteroids exist in our Solar System relatively quietly, moving serenely around without making their presence very obvious to us. In some ways, they are like dormant volcanoes, those that are simply asleep rather than dead, never bothering us in any way. However – and this is where the Jekyll and Hyde nature of comets and asteroids becomes apparent – if a comet or asteroid were heading on a collision course with our beautiful planet, even if it were modest in size, say around 400m (0.25 miles) cross, it would have the potential to unleash all manner of destruction on earth…. Just like those city inhabitants living under that looming volcano and seemingly unaware of its quiet capacity for destruction, humans all over the planet live in blissful ignorance of the deadly potential for the mostly invisible, but possibly violent, comets and asteroids."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
copper	"Copper is civilisation's nervous system"	Ed Conway Material World
copulation	"It's not easy being a sperm. Propelled into an acid mucus bath and forced to swim past an aggressive border patrol that makes immigration staff at Heathrow seem jovial, all to get to an egg that might never arrive."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
Cretaceous-Palaeogene (K-Pg) boundary	"Then the Dutchman, Jan Smit, collaborated with a Belgian atomic and meteoritic expert, Jan Hertogen, and they found, in the bottom part of the Caravaca boundary layer, iridium levels 460 times normal. The discovery was as suspicious as finding traces of arsenic in a dying man, the patient in this case being the sick planet Earth."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
degassing	"However, while it is known that comets and asteroids bombarded the early Earth, and that they contain volatiles, their impacts could have instead helped to de-gas the planet at the same time. I'll liken this process to a stage of baking a cake. Let's think of the Earth as a lump of cake batter. When you put the batter in the cake tine prior to baking, you can tap the tin on the counter top and all the gas bubbles work their way to the top of the batter and pop out. I admit, it's not exactly the same, but a big impact on Earth would have shocked it into releasing its trapped volatiles such as water…. If the impact of water-rich objects preceded a really large impact, such as that which formed the Moon, then any water the Earth had accumulated might have been lost, being degassed away into space (like the bubbles leaving the cake batter)."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
dermatology	"Dermatologists are the Sherlock Holmes of the medical world….When patients come to the dermatologist with a rash it's the dermatologist's job to to hunt down the guilty allergen from the many, many things we come into contact with everyday."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
discovery of Neptune	"Uranus…was not moving as expected. It persistently wandered away from its predicted path, so that clearly it was being perturbed by some unknown body. … It was a sort of cosmic detective problem – they could see the 'victim', Uranus, and they had to find the 'culprit'."	Patrick Moore The Great Astronomical Revolution.
D.N.A.	"Genes are but islands in a sea of DNA."	Neil Shubin Some Assembly Required. Decoding four billion years of life, from ancient fossils to DNA
D.N.A.	"A small region one million bases from the gene somehow controlled the activity of Sonic hedgehog. It was like finding the switch for a light in a living room in Philadelphia on a wall in a garage in suburban Boston."Human embryonic development	Neil Shubin Some Assembly Required. Decoding four billion years of life, from ancient fossils to DNA
D.N.A.	"If you picture DNA as being a bit like a zip, the bases are the teeth that stick out and connect with the opposite side."	Catherine Carver Immune. How your body defends and protects [Read about this book]
Earth in space	"The universe is large and violent, but we survive because our wagon (the Earth) is hitched to a bright but humdrum star (the Sun), far form the tumultuous centre of our Galaxy (the Milky Way). Other stars in our neighbourhood scurry about, but only two interstellar matters are relevant to our parochial story: passing stars occasionally encounter comets wandering far form the Sun, and the Sun sometimes conducts all its family through dark, diffuse clouds of interstellar dust."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
embryonic development	"When a human egg cell begins to divide and create a newborn child it achieves an enlargement equivalent to a lightbulb giving rise to a massive office block 250 metres high; which then, over the next 15 years or so, stretches and widens to an astounding 1,000 metres in height and nearly 250 metres across."	Andrew Scott Vital Principles. The molecular mechanisms of life
enzymes	"The production line analogy is a very good one. The individual 'work stations' are the enzymes, and at these molecular work stations various chemical components are brought together and fashioned into some new component of product. The product of one enzyme can then pass down the line, to become the substrate of the next enzyme, and so on until the pathway is complete."	Andrew Scott Vital Principles. The molecular mechanisms of life
Fermi research group	"He [Enrico Fermi] had soon attracted a team of young, fresh talent who didn't mind breaking, bending or ignoring the supposed laws of the universe…. To them, Fermi was simply 'The Pope', and if said something could be done, they'd do it. Fermi's 'Via Panisperna Boys' were atomic physics' answer to the Sex Pistols: punk scientists who were about to make their own rules." [n.b. an 'answer' that came four decdes before punk.]	Kit Chapman, Superheavy. Making and breaking the periodic table
gene regulation	"Imagine a house with many rooms, each with its own thermostat. A change to the furnace will affect the temperature in every single room, but changing a single thermostat will affect only the room it controls. The same relationship is true for genes and their control regions, Just as a change in the furnace will affect the entire house, an alteration in a gene, and the protein that is produced, can effect the entire body. A global change would be catastrophic, producing dead ends in evolution, But since the genetic control regions are specific to tissues, like a thermostat in a room, a change in one organ won't effect any others."	Neil Shubin Some Assembly Required. Decoding four billion years of life, from ancient fossils to DNA
Graft Versus Host Disease	"Normally the donor cells would be vastly outnumbered and it would be like a band of rebels taking on a vast army on its home turf, but in GVHD the recipient's own immune system is in a weakened state and unable to fight back."	Catherine Carver Immune. How your body defends and protects
grand unified theories (GUTs)	"Cosmology could indeed separate the sheep from the goats, in distinguishing grand unified theories that were plausible from those that were not, but a whole lot of sheep remained."	David Lindley The Dream Universe. How fundamental physics lost its way
haemoglobin	"So the binding of one oxygen molecule to one subunit of an empty haemoglobin complex greatly encourages the binding of oxygen to the other three available sites. This makes the multi-subunit haemoglobin complex a bit like a four-seater car in which the first person into the car unlocks the door for another three passengers….An opposite effect occurs when loaded haemoglobin reaches a tissue in need of oxygen: the loss of one oxygen molecule from one subunit causes a conformational change in the complex which allows the other three oxygen molecules to be off-loaded much more readily. A suitable analogy to this would be an unstable four-man boat, since, if one man jumps overboard, he may rock the boat sufficiently to make the other three fall out!"	Andrew Scott, Vital Principles. The molecular mechanisms of life
heat shock proteins	"heat-shock proteins…can take misfolded proteins and do the protein equivalent of origami to rearrange the mangled protein into a beautiful, functional shape."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
hormones	"Cells achieve such chemical communication in various ways, but the most vital way is by releasing chemical 'messenger' molecules (the biological equivalent of the postal system, if you like analogies)…A biological messenger molecular is more like a legal summons than a friendly note or some junk mail advertisement – it commands the target cell to react in a precise way to the arrival of the message."	Andrew Scott, Vital Principles. The molecular mechanisms of life
immune system	"As we've seen, the immune system is like a very complex game of Mouse Trap, except all the different interconnected pieces work together to catch invading micro-organisms instead of cheese-thieving mice."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
immune system	"Although blocking TNF-alpha [tumour necrosis factor alpha] has a positive impact on these diseases, shutting down a major communication route in the immune system's chattering network can have other[,] unintended[,] consequences. It's a bit like Facebook – we all have friends who share irritating things, but if we cut off Facebook altogether we lose not only the mundane minutiae of people's dietary habits, but also Facebook's benefits. With infliximab, the reduction in TNF's-alpha immune chatter can increase the risk of some serious side-effects including pneumonia or septicaemia, and in children lymphoma, leukaemia and other cancers."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
immune tolerance	"Tolerance…involves teaching the patrolling forces of the immune system to stand down if the cell they're [sic] interrogating is a healthy cell that belong to the body. It's a bit like a border patrol force wandering through the body and checking passports. If a cell shows the correct passport, the immune cells move on; if they don't, the cell is in trouble. Essential to this premise is that the border patrol cells only pick on infected or foreign cells. Unfortunately, the way our multitude of immune cells are made means that some see a healthy passport and attack instead of moving on. The process of tolerance is like a training camp for the newly created border guards, showing them a range of perfectly normal passports representing all of the healthy cell types in the body and ordering those that react incorrectly to self-destruct."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
impact events	"In a world where the nuclear weapons are ready on the instant to defend us against one another by blowing us all up, to fret about cosmic impacts is like worrying about being struck by lightning during the Battle of the Somme."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
inheritance	"Living things do not inherit skulls, backbones, or cell layers from their ancestors – they inherit the processes to build them. Much like a family recipe passed along and modified during each generation, the information that builds bodies has continually changed over millions of years as ancestors pass it on to descendants. Unlike a recipe used in a kitchen, the one that builds bodies anew in each generation is written not in words but in DNA… If the genome is thought of as a recipe, then genes code for the ingredients, and the switches contain the instructions about when and where to add each ingredient."	Neil Shubin, Some Assembly Required. Decoding four billion years of life, from ancient fossils to DNA
inheritance of acquired characterisrtics (Lamarckism)	"He [botanist J. W. H. Harrison] went on to set out a theory by which chemicals eaten by the moth somehow found their way into just that part of the chromosome that controlled the moth's ability to survive the effects of those chemicals. John Maynard Smith quoted another biologist who described the inheritance of acquired characteristics as being 'as if a man sent a telegram in English to China and it arrived of its own accord translated into Chinese'."	Karl Sabbagh, A Rum Affair. A true story of botanical fraud.
interferons	"… it proved incredibly difficult to create pure enough interferons in large enough quantities to conduct high quality clinical trials it was a bit like designing an experiment to assess the effects of alcohol intoxication with only a half-eaten box of chocolate liqueurs left over form last Christmas to test your theory."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
interleukins	"Trying to follow the consequent naming system of the interleukins is like trying to herd some very oddly named cats. One such cat is is interleukin-1…"	Catherine Carver Immune. How your body defends and protects you [Read about this book]
ion channel	"When it is sitting in a polarised membrane, this protein is in a conformational state in which it is unable to allow any ions to pass through the cell. When the membrane around it becomes depolarised, however, the protein undergoes a conformational change which causes it briefly to form a channel through which Na+ ions can pass. The channel only remains open for a short time, however, since the conformational upheaval [sic] of the protein continues until it adopts a new conformation in which the passage of Na+ ions is once again blocked. The overall effect of this conformational change is a bit like the operation of a turnstile…"	Andrew Scott Vital Principles. The molecular mechanisms of life"
leukaemia	"These immature cells are unable to fight infection, and they crowd out the bone marrow, turning the constrained space of the bones into something like a packed commuter train, leaving little space for any normal cells to join the carriage."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
light	"The intention is to pull photons into spinning vortices in a Bose-Einstein condensate, hoping that the light will be dragged into the churning matter like a car sucked into a tornado. If these frigid whirlpools can be spun fast enough, they will become microscopic optical black holes, clawing in light and never letting go until the vortex loses its momentum."	Brian Clegg Light Years. The extraordinary story of mankind's fascination with light.
light	"Moving at this remarkable rate, the experimenters' pulses of light would not be flowing along normally in time. Instead they would be slipping back against the time stream like salmon fighting their way up a river."	Brian Clegg Light Years. The extraordinary story of mankind's fascination with light.
lobotomy	"Surgeons choose the brain targets on the basis of results of past lobotomies and cingulotomies, noting which lesions brought with them relief. The problem is, all sorts of lesions have attenuated anxiety and depression in desperate patients, lesions to the left or right, up or down, here or there. Without a single sweet spot, the possibilities are disturbingly numerous. No one in his right mind would get on a ship if the captain wasn't sure where to steer. But of course that's the point. Psychiatric patients who have this surgery are no longer truly in their right mind. They get on board because this is their last lifeboat."	Lauren Slater The Drugs that Changed our Minds.
longitudinal waves	"The wave transfers energy across the water like a chain of people passing boxes along – the people (the water) don't move sideways, but the boxes (the energy) do."	Brian Clegg, Light Years. The extraordinary story of mankind's fascination with light.
macrophages	"…we are riddled [sic] with munching macrophages. The majority of macrophages are stationed at strategic sites that provide the best pickings of microbes and dead cells. For instance, the liver is a veritable smorgasbord for the residents macrophages, which dine on aged red blood cells and bacteria freshly delivered from the gut…."what an important outpost the liver is for the immune system."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
mathematical universe theory	"An elementary particle is then a line weaving its way through this through this landscape [of numbers and quantitative relationships that extends throughout space and time] as it moves through both space and time. A human being is a collection of atoms, except that it constantly exchanges atoms with the outside world (breathing, eating, disposing of bodily waste, shedding skin cells…), so we have to think of a person as a sort of complex braided thread in the mathematical landscape, with fibres both entering and leaving it."	David Lindley The Dream Universe. How fundamental physics lost its way
metabolism	"I have drawn an analogy between the creation of living things containing many high energy chemicals…, and the raising water vapour from the sea into the sky. We can continue with this analogy as we look deeper into the energetics of the living cell…"	Andrew Scott, Vital Principles. The molecular mechanisms of life
meteorites	"some 40,000 to 80,000 tonnes of space rocks fall onto our planet each year. These free space samples can be likened to cosmic Kinder Eggs – they are packed with celestial prizes, information about our Solar System."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
microbiome	"…the human microbiota is the collective name for the 100 trillion micro-organisms that have made us their real estate. From the tip of your tongue to the skin you sit on, they have set up home in every intimate nook and cranny of our body…The prime real estate for these microbes, the Manhattan or Mayfair equivalent inside you and me, is the large intestine or colon. If you had a Lonely Planet or Rough Guide to your gut, the colon would have an entry something like this: 'The colon is a must-see multi-cultural melting-pot, where up to one thousand species of bacteria mingle and dine together every second of every day. In this truly 24/7 subterranean city ….[antibiotics] potential to kill off vast swathes of the normal gut flora. This creates an open-plan living space for a hardy bacterium called Clostridium difficile. This so-called superbug (also known as C. diff) is able to survive the initial antibiotic onslaught and then rapidly multiplies in its newly vacated palace."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
microbiome	"So it seems our gut bacteria effectively provide a training ground for the immune system – a boot camp led by billions of bacteria which teaches us to develop an arsenal of antibodies to tackle common foreign invader fingerprints like alpha-gal."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
microbiome	"…the study could not answer these questions [about links between gut bacteria and premature babies]. Instead it lobbed a few more pieces into a puzzle box that is already full of bits of various shapes and sizes, some of which aren't even part of this jigsaw. Also there's no picture of what the completed puzzle should look like and we've no idea how many pieces we should expect to find. Yet there's hope in the impossible mission because some scientists raking through the box of the microbiome jigsaw puzzle think they've fished out some edge pieces."	Catherine Carver, Immune. How your body defends and protects [Read about this book]
microbiome	"We continue collecting various microbes throughout the first few months and years of life, like a bacterial version of baseball cards or Pokemon Go."	Catherine Carver, Immune. How your body defends and protects [Read about this book]
molecular clouds (in space)	"This is why molecular clouds are sometimes called 'stellar nurseries', because they have the potential to give birth to a whole crèche of baby stars."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the solar system
natural history (plant identification)	"[amateur naturalist, John] Raven of course had…a memory that had practiced for two decades what psychologists refer to as pattern recognition, whereby the regular occurrence of several different features is immediately recognised as significant in a way that any individual feature might not be. It's rather similar to the way police profile a criminal by different aspects of his modus operandi and ascribe a series of unsolved crimes to one perpetrator. Similarly, the natural occurrence of a plant in a specific location is usually accompanied by a 'pattern' of other facts – soil type, neighbouring species, terrain, temperature range, latitude, and so on."	Karl Sabbagh, A Rum Affair. A true story of botanical fraud.
neural basis of memory	"Sacktor compares [enzyme] PKMzeta to a sheepdog, because the molecules do one thing in a persevervative fashion: they 'herd' AMPA receptors, which are membrane proteins crucial to receiving neural signals. Once the receptors are sandwiched between the nerve cells it is the job of the memory molecule to make sure its AMPA receptors do not drift, thereby ensuring that memory remains cohesive during chemical cascades."	Lauren Slater The Drugs that Changed our Minds. The history of psychiatry in ten treatments.
near earth objects	"The closer the object is to Earth, the larger the required force would be to change its trajectory adequately for it to miss the planet. If you imagine throwing a dart at a board, it's much easier to hit the target if you stand close to it. If you stand very far away from the board, then you are more likely to miss the target because a small change in the angle at which you release the dart will be amplified over the greater distance it travels."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
neurons	"So any single nerve cells acts like an [sic] tiny automatic ballot machine, assessing the number of 'yes' and 'no' votes entering it at any one time and either firing or not firing depending on which type of vote predominates at any one time. …Nerve cells receive electrochemical signals from other cells, and each signal represents a 'yes' or a 'no' vote in an election to determine whether the cell should fire."	Andrew Scott, Vital Principles. The molecular mechanisms of life"
neutrophils	"Finally, the cell contracts itself tightly before exploding like a party popper that releases deadly NETs [neutrophil extracellular traps] instead of streamers."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
neutrophils	"…much of the knowledge we have is from looking at neutrophils in a petri dish, which is a much simpler environment than the human body. It's a bit like looking at animals in a zoo versus in the wild – you can see a lot of what they get up to but it doesn't mean tap-dancing is normal penguin behaviour."	Catherine Carver. Immune. How your body defends and protects you [Read about this book]
neutrophils	"A third neutrophil strategy is less elegant but nonetheless effective: spewing microbe-dissolving chemicals into the surround tissue. This allows the neutrophil to damage many microbes at once, a bit like fishing by throwing dynamite into the water. However, like dynamite fishing this technique lacks finesse and can cause significant injury to the surrounding tissue"	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
Newtonian physics	"To suggest that Newton's system of the world was only a little bit wrong is like reassuring a corpse that it is only slightly dead."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
nuclear fission	"Creating an element was walking a tightrope: you needed energy to push past the Coulomb barrier in the first place, but if you used too much energy the nucleus would literally shake itself apart. In other words, the nucleus acted like a fuse box: too much energy and the fuse blew."	Kit Chapman, Superheavy. Making and breaking the periodic table
nuclear fission	"…a 'fissile' isotope – one that, if hit by a neutron, will send neutrons flying out in turn, like a pool ball hitting the stack."	Kit Chapman, Superheavy. Making and breaking the periodic table
nuclear reactions	"If light-ion-induced reactions are a bombastic slamming together of two nuclei, a SWAT team kicking down the atomic door, cold fusion is a surgical ninja strike, stealthily squeezing just under the Coulomb barrier with the minimum energy possible."	Kit Chapman, Superheavy. Making and breaking the periodic table
nuclear stability	"The new model of the nucleus was the biggest shift in fundamental particle science since the 1930s. The chemical world opened as if a map had been unrolled, with the number of protons and neutrons as the axes. The stable elements existed on a long, thin peninsula that arched towards the top of the chart before dipping away. One either side was a 'sea of instability' – where the whole nucleus would break apart. … the Berkeley and Dubna teams were creating the elements at an imaginary cliff edge that marked the end of stability, where the peninsula fell away into the sea. … In both the US and USSR, the teams realised that if you could create a nucleus with a 'magic number' of protons or neutrons, the newly created element would be far more stable than anything they had made before. Continuing the theme of peninsulas and seas, they began to refer to these nuclides as being on 'the island of stability'."	Kit Chapman, Superheavy. Making and breaking the periodic table
organisation of multicellular organisms	"The organization of bodies is much like Russian dolls: bodies contain organs that are composed of tissues that are made of cells that have organelles, all [sic*] of which have genes inside." [This is an odd choice of analogy because Russian dolls consist of similar units that differ only in scale.] * Note: Not all organelles have genes inside: some do (e.g. mitochodria) but other are coded for by nuclear genes.	Neil Shubin, Some Assembly Required. Decoding four billion years of life, from ancient fossils to DNA
panspermia	"…if we earthlings are to be kept sweating in the isolation wards, there must be many pathogenic comets which use the same genetic code as we do. Otherwise the viruses will be as ineffectual as a car key in a padlock."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
parasites	"It's as if the trypanosome has a bag of hats that it can whip out and use to play dressing-up to outwit the immune system. Initially all the trypanosomes in the body are wearing purple fedoras but by the time the immune system has figured out how to make anti-purple fedora antibodies, some of the parasites have had a rummage in their genetic dressing-up kit and popped on a pink bowler hat instead. The pink bowler brigade are immune to the anti-purple fedora antibodies and therefore persist in the body and multiply. The trypanosomes have about 1,000 hats at their disposal, which means this cycle of deadly dressing-up goes on and on, allowing them to thrive for years."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
parasites	"Responding to the presence of molecules secreted by the [bacterium] Wolbachia, neutrophils surround the [parasitic] worm and begin breaking down the chemicals its bacterial side-kick has been producing. But these chemicals are like a glamorous magician's assistant shaking its tassels and flashing its feathers to direct attention away from what's [sic] really happening…"	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
particle accelerators	"…you still had to hit the nucleus, something unimaginably small. 'You see', Albert Einstein said dismissively in 1934, 'it is like shooting birds in the dark in a country where there are only a few birds'. Einstein was right. Yet even in a dark country [sic], you'll eventually hit something if you if you keep going for long enough. The nucleus had been hit before – and the cyclotron effectively gave everyone a super machine gun with an infinite supply of bullets." "In principle, the U400M [the U stands for uskoritel, or accelerator] – is exactly the same as the first generation of cyclotrons: an ion machine gun. It just happens to be a machine gun the size of a house that fires 6 trillion bullets per second."	Kit Chapman, Superheavy. Making and breaking the periodic table
particle accelerators	"The Australian team use their accelerated beams to work out the best ways to form superheavy elements: what energies are needed and how the reactions will behave. …ANU [Australian National University]'s work means the element hunters now have a better idea about what beams and targets to try, and where to look. 'It's like Where's Wally', [experimental physicist Nanda] Dasgupta explains. 'Wally is hidden somewhere in a load of pirates. We're getting rid of the pirates, taking Wally and putting him in the detector'."	Kit Chapman, Superheavy. Making and breaking the periodic table
penis	"Unfortunately, the penis is like a slightly underfunded public transport service, taking the sperm a fraction of the way to their final destination and dropping them prematurely in an unsavoury neighbourhood."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
perforin	"While our understanding of perforin is evolving, one theory is that it behaves like a Trojan horse….At the same time that it pulls in the perforin holes, the cell unwittingly pulls in a family of protein-eating granzymes…"	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
periodic table	"Lavoisier set about putting together a list of these 'chemical elements'…In 1869 a Russian Chemist, Dimitri Mendeleev, ordered them into what we call the periodic table. This was an astonishing feat – the equivalent if putting together a globe-spanning jigsaw puzzle without knowing the picture, the shape of how many pieces came in the box." "The heavy element community weathered the greatest storms of the twentieth century and kept on building the jigsaw of our world." [These quotes are separated by over 260 pages. Without this context from eaerlier in the text I would class the second quotation as a metaphor.]	Kit Chapman, Superheavy. Making and breaking the periodic table
planetary change	"However, the hefty size of the planets meant that they experienced extensive geological re-processing, melting and re-melting in the intervening years since they formed.The planets have essentially cooked their original solar nebula ingredients, transforming them into other mineral and rock assemblages that obscure the early Solar System history their raw ingredients held. It's a bit like the ingredients for a cake, which are then mixed and baked. The end product looks very different to the pile of flour, sugar and eggs the baker started out with. Most people would struggle to identify a cake's recipe with only the final baked product to work with. They might guess at the majority of the ingredients that were added, but they probably couldn't work out the exact quantities. After all, most people follow a recipe to bake a cake, with a list of ingredients that are needed and in which quantities to add them` to achieve a tasty concoction. With a planet, all that's left is the end product, the cake. Which is obviously great but it would be useful to know how it was produced if you liked it. Only then can scientists start to understand what the conditions were like early in Earth history at important times such as when life began."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the solar system
plasma cell	"…once the B cell finds an antigen its receptor can bind, like Cinderella fitting her foot into her glass slipper, the B cell is transformed, and slightly less like a Disney princess, becomes a plasma cell capable of firing out antibodies into its surroundings."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
preformation (historical theory)	"According to preformationists, every creature currently alive stems from an original act of creation by God. The first member of each species contained within it all future offspring, so that like Russian dolls being unpacked, latent embryos exist already fully formed [sic]: effectively, miniature babies simply get bigger before being born."	Patricia Fara Erasmus Darwin. Sex, science and serendipity
prostaglandins	"Essentially, rather than releasing a pack of really hungry Rottweilers, PG [prostaglandin] E2 keeps our vicious immune cells on a tight leash, limiting their ability to go on the rampage and unintentionally damage our own cells."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
proteins	"Structural proteins are often referred to as the molecular scaffolding of life, and the analogy is quite apt since so many structural proteins are long fibres or rods; but we think of scaffolding as a static, unchanging, framework. Imagine, however, a structure built of scaffolding in which some of the scaffolding rods were able to slide past one another and then hold the whole framework in new positions."	Andrew Scott Vital Principles. The molecular mechanisms of life
quantum mechanical wave function	"Schrödinger's formulation of quantum mechanics described particles in terms of a wave function, a mathematical description amount to a spread-out fogginess rather than a specific location. That fogginess was identified, a year or so later, as the probability of a particle's location at a certain point: the denser the fog, the more likely it was that an experiment would find the particle at that position."	David Lindley The Dream Universe. How fundamental physics lost its way
quantum physics	"Quantum physics is a vast country with a rich and deep culture. If all you know about it is that it has 'unravelled the age-old enigma off the mysterious country of the microworld', and also brought about an 'upheaval in our entire view of the world', then you know as much about it as tourists know about an unfamiliar country whose culture is foreign to them and whose language they do not understand."	L. I. Ponomarev The Quantum Dice
quantum theory	"Quantum theory says that a light photon can exist in a strange mixture of two possible states until it is measured – only then does it decide which it is going to be. It's as if a child were both a boy and girl right up to the point it was born and it was only at that moment that a coin was tossed and the 50:50 decision made."	Brian Clegg – Light Years. The extraordinary story of mankind's fascination with light.
radiation damage	"In certain materials, radioactivity produces a strange halo effect – a spherical zone of discolouration caused by radiation damage. Usually, slicing through these halos and looking at them under a microscope gives a neat ring structure, much like cutting through a tree, with each ring showing just how far some alpha particles managed to scatter."	Kit Chapman, Superheavy. Making and breaking the periodic table
scientists	"Scientists in pursuit of enlightenment from nature will always behave like men competing for the same woman."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
Solar System	"To make the Solar System easier to picture, I like to think of it as a city, with the different parts of it as neighbourhoods. The planets, comets and asteroids are all part of the overall city and its suburbs in some way, but the places where they are found represent very different areas of it, from the busy and lively downtown communities (i.e. the planets of the inner Solar System) to the quiet, calm and more sparsely populated suburbs (i.e. the comets.)" "The size of the Solar System, and the problems in visiting its farthest corners, mean that scientists are still drawing a detailed picture of what the real estate surrounding our average star contains, and trying to understand how it formed." "Before the planets formed, the Solar System was nothing but a swirling cloud of gas and dust, which was itself travelling through space. If we want to draw on the Solar-System-as-a-city metaphor here, we can think of this as the peaceful and luscious green countryside existing before our metropolis was built. This swirling cloud eventually became the construction site for everything we see [sic] today, including the planets, asteroids and comets, from the largest gas giant, Jupiter to the smallest specks of dust that travel around in the space between the planets. The outer edge of this cloud eventually became the immensely cold and far fringes of today's Solar System – places that are hard to see from Earth with even the most powerful telescopes, where barely any of the Sun's energy can reach. This represents the true outskirts of our city, the boroughs that barely feel like they are part of the conurbation at all. Many comets formed at the very edge of this cloud and for well over 4 billion years they have lingered in this remote neighbourhood. These comets are so far away that they could be represented by the rural communities that often surround large cities. In the same way that daily life in these farming regions is little affected by the hustle and bustle of the capital, these comets have been able to remain perfectly in deep freeze, preserving the early captured planet-building ingredients that they scooped up billions of year ago." "We can think of asteroids as the as the leftover Solar System building rubble that wasn't incorporated into one of the major city skyscrapers, or planets in the case of the Solar System." "One of the problems of sampling and measuring comets and asteroids is that they reside very, very far away from Earth. In fact, much like the city dweller without access to a car who never ventures out as far as the greenbelt, no spacecraft has ever travelled as far as the outermost comet neighbourhood. Luckily, comets and asteroids occasionally exit their cold, dark home and pay a visit to the inner Solar System. We can, perhaps, think of these objects as the out-of-towners travelling into the city fro some weekend sightseeing. These people zoom through the outskirts of the town on their high-speed train line, just like the comets and asteroids that whizz past the planets on their orbits around the Sun. When these usually far-flung space objects make such journeys, it gives scientists a fighting chance of getting near enough to them , within a reasonable timeframe to study them up close." "Despite the fact that we may have to thank comets and asteroids for our very existence here on Earth, there are some serious downsides to them entering the city centre of the Solar System." "One of the cometary neighbourhoods, the so-called Oort Cloud, is so far out that it is barely within the gravitational grasp of our star. This is the region of the Solar System that we likened to the rural communities existing in the greenbelt surrounding a city, each one located a great distance form the others, but all looking similar in nature. The closer comet neighbourhood is the Kuiper Belt, sometimes known as the Edgeworth-Kuiper Belt, which is still 10 times further from the Sun than the asteroid belt. The Kuiper Belt acts much like the outer suburbs of the city, not quite the very edge, but a journey into the city would be a long and arduous one." "Some estimate suggest that the outer edges of the Oort Cloud may even be closer to the next star system than to our own Sun. These icy objects really are [sic] those more remote rural farms that are as close to our Solar System city as they are to the neighbouring city, yet still a great distance from both.It is the gravitational influence of passing stars, and even the Milky Way itself, that can perturb and tug at the outer Oort Cloud comets, loosely bound to the Sun because of its weak gravitational influence at this distance, disturbing them from their orbit and sending them careering into the inner Solar Systm. Perhaps if we stretch our Solar System-city metaphor a bit further we can suggest that these comets are like the farm workers who seldom get a night off from their hard labouring, but when they do they travel a long way to the city for a wild night out." "Even if objects were formed in the far outer reaches of the Solar System, they haven't necessarily ended up staying there permanently, and vice versa. Much like the inhabitants of our Solar System-city having moved around throughout their lifetimes, perhaps starting their young life in the suburbs, migrating for work to the bright lights of the city and eventually back out again as they grow older, the Solar System objects have, in some cases, experienced a similar life." "The fact that the comet-forming region in the outer Solar System is vast, and sparse, means that most comets are separated by at least several hundreds of kilometres. Remember the analogy to those remote farms situated on the outskirts of the city?" "The results show that you can't judge one comet by another, even those that grew up in the same neighbourhood." "This applied, in particular, to the long-period comets that can appear in the inner Solar System rather unexpectedly, on a random orbit, after departing their home in the Oort Cloud."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
Solar system	"The opening days of the solar system…all the ingredients required to form an entire Solar System, including the ones necessary to create complex organisms like ourselves. To get to where we are today, these ingredients needed some processing. This was essentially mixing and baking at high temperatures, so we can think of the development of the Solar System as a sort of extreme cookery book."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
space dust collectors	"The collector pods are packed in a super-clean laboratory environment prior to flight and are made up of a flat collector plate covered with silicon oil that acts a bit like sticky flytrap paper except that, in this case the flies are bits of space dust."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
space-time	"While time and space were relative, the combination of them was absolute. This is similar to how people facing in opposite directions will give different directions for turning left or right but can both agree about whether you should turn north or south."	Matthew Stanley: Einstein's War. How relativity triumphed amid the vicious nationalism of World War 1
space winds	"It was hypothesised that strong jets, or turbulent winds, that are thought to have been active very early on during the collapse phase of the solar nebula, could have been capable of transporting newly formed solids from next to the Sun all the way out to the comets. … Just like a desert wind picking up sand, it is proposed that these windy jets could transport chondrules and CAIs [calcium-aluminium-rich-inclusions], or fragments of them, rapidly flinging them out of the inner Solar System to be deposited in the cold comet-forming region as the winds lost momentum."	Natalie StarkeyCatching Stardust. Comets, asteroids and the birth of the Solar System
special relativity	"Fixing light's speed has the effect of freeing up other factors that had until then seemed unchangeable. It's like trying to pin down an animal so a vet can give it an inoculation. Hold it by the legs and its head moves too much. Grab for the neck and the legs are suddenly kicking out. When Einstein pinned down light's speed, not only mass and size, but time itself, sprang free."	Brian Clegg Light Years. The extraordinary story of mankind's fascination with light
spin-orbit coupling	"This was linked to an idea called spin-orbit coupling, which [Maria] Goeppert Mayer explained like a ballroom full of waltzers, all going around a room in circles (the spin). On the dance floor, it's much easier for the waltzers if they are all circling and twirling in the same direction as it requires less energy. When she hit certain numbers – when the nuclear shells were filled – everything was at its most tightly bound. The dancers took up the ballroom but had enough space to look elegant and ordered as they glided across the floor. Add too many dancers, though, and they interrupt the flow. By spotting when there was a big difference in energy when another proton or neutron was added when the dance was being disrupted – Goeppert Mayer could identify where the shells started and finished."	Kit Chapman, Superheavy. Making and breaking the periodic table
spleen	"Very rarely though, something goes awry in the earliest stages of embryo development and the spleen ends up in the wrong place. This isn't necessarily as bad as it sounds; in some cases it's like having a stranger unpacking our groceries and putting them in the wrong cupboards – it's not quite right but it's not actually a problem."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
stars	"The planets wander slowly around the sky, whereas to all intents and purposes the stars do not – hence the old term of Fixed stars. And the reason can be summed up in one word: Distance. The farther way a moving object is, the slower is seems to go. A bird flying between the tree-tops appears to shift much more quickly than an aircraft seen against the clouds, even though its true speed is very much less."	Patrick Moore The Great Astronomical Revolution
stimulated emission of radiation	"According to Einstein's theory, an electron in an atom can be pushed into a higher energy state when it is hit by a photon, leaving it like a bucket of water sitting over an open door. Another photon, hitting that electron, would not only be re-emitted itself, but would trigger the electron to release the stored up energy as a second photon – as if the bucket was knocked off the door by the stream of water from a hose, resulting in a doubled downpour."	Brian Clegg Light Years. The extraordinary story of mankind's fascination with light
string theory	"The elegance of string theory manifests itself clearly only in its natural habitat, a high-energy universe of ten or eleven dimensions. What we can see, poor inhabitants that we are of a broken-down low energy four dimensional world, are merely the ragged remnants of that intrinsic beauty, clumsy fragments of a perfect creation form which we hope to deduce, in circular fashion, the existence of an elegance that must always be hidden from our direct view. We are like Plato's cave dwellers of old, struggling to infer form the fleeting, cryptic shadows on the wall the hidden reality of a perfect, constant sun."	David Lindley The Dream Universe. How fundamental physics lost its way
synthesising elements	"In 1986, at the request of the Germans, the governing bodies of chemistry and physics, IUPAC and IUPAP [International Union of Pure and Applied Chemistry;  International Union of Pure and Applied Physics], assembled a working group to settle the debate surrounding the superheavy elements. Known as the Transfermium Working Group (TWG), its members had to define when an element counted as being made, and who had got there first. It was like playing the first-ever game of football, only for the referee to explain the rules and work out who scored first after the match had ended."	Kit Chapman, Superheavy. Making and breaking the periodic table
T cells	"It's the T cell's job to spot infected or abnormal cells. Stick in an organ from someone else and it's like putting a pink polka-dot cushion on a zebra-print couch – the clash is impossible for the T cell to miss."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
T cells	"T cells interact with their quarry through a T cell receptor, which pokes out of the cell like the eye-piece on a Darlek."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
T cells	"These different receptors are essential to a highly complex secret handshake that occurs between the T cell and cell presenting the mushed-up microbe to it. In the case of helper T cells and professional Antigen Presenting Cells, one party has essentially spat on its hand as the APC's extended receptor includes a gob of antigen the cell has chewed up internally before proffering it to the T cell….The second element of the handshake acts to bolster this grip as additional receptors on the T cell hook up with their dancing partners on the surface of the surface of the Antigen Presenting Cell…"	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
tectonic plates	"The outermost shell of the Earth can be likened to a massive jigsaw, but with seven major pieces, and some smaller but no less significant pieces. The Earth's major jigsaw pieces, encompassing areas greater than 20 million km2 (7.7 million sq miles), are the tectonic plates that carry the landmasses. But unlike a normal jigsaw, these plates jostle for position as they attempt to seamlessly float on the Earth's somewhat squidgy underlying mantle."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
testing theories	"One of the things you do with a possibly complete theory is try to use it to solve problems. Does it give a better explanation for old problems than the theories we already have? Does it help solve a problem that we haven't made any headway on? Does it tell us about a problem that we didn't even know was a problem? Einstein was trying all of these. It's much like when you have a new wrench in the workshop – you try it on all the stuck bolts that you have sitting around. Hopefully it works better on them than the old wrenches and still works just as well as them on the old projects. Most of all, it should let you build something new that you couldn't before… This was a new wrench that Einstein was checking against old bolts. He was already happy with how the Entwurf handled conservation laws, but a new wrench is a new wrench – he couldn't not try it out. It seems that while he was checking out the conservation laws he decided to take a look at some other old bolts too. Specifically, rotation. …" "Einstein was now extremely pleased with his equations, and it was time to start testing them on the old stuck bolts that had been bothering him. He sat down to calculate the perihelion shift of Mercury with his new tools – and the bolt moved."	Matthew Stanley Einstein's War. How relativity triumphed amid the vicious nationalism of World War 1
theory change	"Eddington knew he needed to persuade the British scientific community that relativity was important and interesting enough to spend scarce resources on. He was an apostle bring good news to a strange land. What he needed was some scripture – a fundamental text that he could point to and say, 'This is what relativity means'. … As is often the case when trying to convert a land to a new belief system, the locals in Britain already had their own deity: Newton. Most scientists were perfectly happy with the Newtonian system and did not appreciate Eddington's missionary efforts." "To convert the heathen Newtonians [Eddington] needed to finish his scripture, what would eventually become his Report on Relativity."	Matthew Stanley: Einstein's War. How relativity triumphed amid the vicious nationalism of World War 1
toxoplasmosis	"…Toxoplasma has the less distressing and more intriguing ability to relieve mice of their inherent fear of cats – like a super-unhelpful hypnotist with a vendetta against mice."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
transplants	"Therefore the immune system saw the cells of the brand spanking new vagina [grown in vitro from body cells] as familiar old friends in a slightly different venue…"	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
transplants	"So the next stage in disguising the [transplanted] pig cells has been not only to remove the tell-tale carbohydrate marker that screamed 'pig cell' but also to add in genes for human markers. A bit like handing the pig cell a fake moustache and glasses to confuse the immune system."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
truth	"Here knowledge of the truth alone alone does not suffice; on the contrary this knowledge must continually be renewed by ceaseless effort, if it is not to be lost. It resembles a statue of marble which stands in the desert and is continuously threatened with burial by the shifting sand. The hands of service must ever be at work, in order that the marble continue lastingly to shine in the sun."	Albert Einstein giving a talk in New York
universe	"In the medieval scheme of the universe…the Earth was at the centre of the universe, and the Moon, the Sun and the five known planets were perfect bodies, each fixed on a perfect crystal sphere that revolved about its axis at the appropriate rate. The spheres nested inside one another like Russian dolls and the eighth sphere, mentioned by Tycho, carried all of the 'fixed' stars."	Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley
vaccines	"take a living microbe and weaken it in a lab to create a live, attenuatedvaccine. It's a bit like taking the microbe, tying its hands behind its back, then setting the immune system on it…[but] the microbe's hands don't necessarily remain tied for ever – as it multiplies and mutates there is a remote possibility that the microbe becomes capable of causing the diseased again."	Catherine Carver. Immune. How your body defends and protects you. [Read about this book]
vaccines	"Influenza, like many microbes, betrays its presence to the immune system through tell-tale antigenic makers on its surface. It's a bit like wearing a Red Sox shirt in the midst of a gathering of die-hard Yankees fans, or a Man City one in a crowd of Man U supporters (epic fail). A third form of vaccine design, called the subunit vaccine, takes advantage of this concept by creating vaccines made just form the bits of the microbe that incur the wrath of the immune reaction – the Sox logo or the pale blue shirt in our sports fan analogy."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
vaccines	"Some bacteria have a sugar-based cloaking device that makes it particularly hard for the immature immune system of young children to recognise them. Conjugate vaccines get round this by giving a dose of the cloak that has had a recognisable marker stitched on to it. A bit like throwing a handful of dust onto the invisibility cloak, this helps the body recognise the cloaked bacteria, and should it ever be infected with the disease the immune system will swiftly spot the intruder and neutralise it."	Catherine Carver Immune. How your body defends and protects you [Read about this book]
vaccines	"So in the case of the recombinant rabies vaccine, another type of virus called vaccinia virus is rendered harmless and then made to express rabies surface markers. It's a bit like making vaccinia wear a very realistic rabies mask, and it does an excellent job of teaching the immune system what rabies looks like with zero risk of actually causing rabies…"	Catherine Carver Immune. How your body defends and protects you [Read about this book]
viral evolution	"Information is transferred by gene in much the same way as it is by words. For each, evolution is inevitable…For the human immunodeficiency virus, changes within a patient – a mere shift in genetic accent – or in the particles that pass from one victim to the next track its evolution over months or years. If (and the assumption is a bold one) the limbs of the AIDS tree follow the same rules as those of its twig, the epidemics of today, it should be possible to work out the past growth of any branch, however ancient. To compare the human immunodeficiency virus with its distant relatives – the Chinese-speakers of the viral world – hints at the origin of the plague itself."	Steve Jones Almost Like a Whale: The origin of species updated
volcanoes	"I think of an active volcano as a rocky Jekyll and Hyde – one minute so calm, and the next so angry."	Natalie Starkey Catching Stardust. Comets, asteroids and the birth of the Solar System
waves	"If you imagine a wave – a ripple in a skipping rope, for example – moving at a fixed speed, the more ups and downs there are, the closer together they will be. Think, for instance, of a sewing machine needle diving up and down through a piece of cloth as the cloth moves steadily along. The faster the needle makes up and down movements, the closer together the stitches are."	Brian Clegg Light Years. The extraordinary story of mankind's fascination with light.

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Some examples from broadcast media

nature of science

• "science…is a bit like having a jigsaw puzzle"

Target	Analogue	Analogy	Source
ancient D.N.A.	old parchment	[Svante Pääbo sequencing the genome of the Neanderthal] "it's kind of like trying to read a parchment that you've found from the Holy Land in the time of Jesus and it's all ragged and faded and its very, very painstaking work".	Science Journalist Philip Ball interviewed on BBC Inside Science
bacterial quorum sensing	teenager behaviour	"I use the analogy that bacteria behave a bit like teenagers. They're constantly messaging each other and signalling when there is a high concentration of bacteria present in the same location by throwing a party when the parents are out of town."	Dr Susan Woods, Senior research fellow, Gut Cancer Group, South Australian Health and Medical Research Institute, speaking on Ockham's Razor
Betelgeuse [red supergiant star]	poorly loaded washing machine	"Basic physics says that when you have a star, of that mass, and that radius, it's going to go in and out and pulsate on [a period of] 400 days, but after the mass was ejected it starts ringing with a much shorter period, in other words, it's not 400 days any more it's, oh, 200, 180, and it getting brighter and dimmer much faster than it ever has in over a century, and it is as if the star is trying to recover itself. The analogy that we have been using is that it's like when your washing machine goes out of balance, you know, and it starts not quite getting back into the normal behaviour."	Dr Andrea Dupree, Associate Director Center for Astrophysics, Harvard & Smithsonian (interviewed by Roland Pease on BBC's 'Science in Action')
cartenoids as accessory pigments	sunscreen	"Phytoplankton, if they are in the very surface waters, are in light intensities which are sufficiently high, that the energy coming in from above from the Sun, is sufficiently energetic that they are unable to process all of the light that comes into them. … they create further pigments, and these pigments, these photoprotectant cartenoids, they absorb light and they dissipate it as heat, so basically it's acting as this factor 50 sunscreen for phytoplankton."	Christopher Lowe Lecturer in Marine Biology at Swansea University, talking on an episode of BBC In Our Time
climate change	meteor impact	"Sometimes we may need to visualise like climate change is this meteorite that is coming against the earth. It just keeps getting closer and closer. We need to be mindful of many other challenges that we have globally, but climate change is the biggest challenge that we have now, and that meteorite is only getting closer."	Professor Mercedes Maroto-Valer, Director of the Research Centre for Carbon Solutions at Heriot-Watt University, interviewed on an episode of BBC's The Life Scientific
dark matter	a car taking a corner	"It was the work of people like Vera Rubin who was measuring the way galaxies are spinning, and finding that they spin very quickly, even far out into their outskirts, and the question was, how do they keep spinning? If you imagine you are in a car and you take a corner really fast what will tend to happen is that you will sort of fly off the road. And if you do the calculations you find those stars on the outskirts of galaxies are going so fast they ought to just be flying out of the galaxy into deep space, there is nothing to keep them in there, [MC: interjects "but there is something"], but, but [MC: "there must be something"] so the inference was, well there must be something there providing an extra force of gravity to keep it sort of glued in like you have got extra grippy tyres or something. So that extra stuff, became known as dark matter."	Prof. Andrew Pontzen Professor of Cosmology, UCL, talking to Marnie Chesterton on BBC Inside Science
dating artefacts with post-infrared stimulated luminescence	different capacity rechargeable cells	"…the method looks at the sediment grains… and what we are doing with this method is dating the last time they are exposed to daylight. … they have the property that they can store energy within those grains. And they get that energy from the radioactivity in the surrounding sediment… And so while they're buried, they build up that energy from the radioactivity and the the longer they are buried the more energy is in them. … they produce light…and essentially the brighter that light is, the older the sediment is, the more energy it had stored in it. …the signal starts building up as soon as the sediment's buried …. And in the past we've used quartz a lot…but in the same way as with rechargeable batteries in your phone, once they are full, they're full, and they won't take any more charge. In the same way, these mineral grains, once they've absorbed a certain amount of energy they can't absorb any more, and with quartz they reach the limit of when they're saturated maybe a hundred, a hundred and fifty thousand, years ago. …so we've used a different mineral, we've used feldspars, and by analogy they've got the bigger rechargeable battery, so they can go back further in time."	Prof. Geoff Duller, Department of Geography & Earth Sciences, Aberystwyth University, interviewed on BBC Inside Science
drug cocktails (used in complex regional pain syndrome)	military strategy	"The chemicals spread through Poppy's body, all the way to the spinal cord, and there they reach something that Deepak describes as a series of junction boxes. These junction boxes receive pain signals, and either turn them down or up, and what the ketamine does is to tell these junction boxes to turn the pair signals down… Deepak gives Poppy other drugs too. Each one calming her nervous system at a different point in the circuit. It's like fighting a battle by spreading your troops, rather than going in with a bomb."	Helena Merriman presenting 'Room 5' Episode: Poppy
endocrine system	central heating thermostat	"So it's a bit like a thermostat running a central heating system in the way that they talk to each other, so if we think of the hormones circulating round in the body as like the room temperature, if they go up too high then the signals from the pituitary and the hypothalamus will get switched down, like the thermostat. And then vice versa if the temperature goes down or the hormones go down then the pituitary and the hypothalamus will switch up to make more hormones to be produced."	Rebecca Reynolds – Professor of Metabolic Medicine at the University of Edinburgh, speaking on an edition of BBC's In Our Time
'entanglement' of proteins in synthetic replacement cartilage	spaghetti	BT: "Hongbin was looking for a way to get the protein chains in his hydrogel to stick together in a way that would increase the stiffness without making the material brittle. And, he and his team did this by jumbling them up, using a process called entanglement, which he likens to something that happens when you are eating spaghetti." HL: "Because the individual spaghetti strands, when you try to pull one, so probably you are going to get a few, together, because they are kind of 'entangled', so they are not, kind of, isolated individual ones."	Benjamin Thomson talking to Prof. Hongbin Li, (Department of Chemistry, University of British Columbia) on the Nature Podcast.
fossil fauna from the Middle Ordovician (about 462 million years ago)	archaeology	"Till now we've never had this type of preservation at this age. In archaeological terms, it [discovery of the Castle Bank fauna] would be like finding Tutankhamen's tomb, or something like that, it's an entirely new angle on an area we did not know much about."	Dr Joe Botting, Amgueddfa Cymru (Museum Wales) taking on BBC 'Science in Action'
gene editing	cycle maintenance	"CCR5 is there for a good purpose, it's part of the immune system, you don't mess around with the immune system because even though it may have some kind of effect, protective effect, with regard to HIV, you are still actually messing around it's like, you know, tampering with your brakes, effectively"	Roland Pease (science journalist), 'Science in Action', 10 June 2019
graphene	jigsaw	"Who knew, but it is not easy to work with sheets of semiconductor just an atom thick, think of the last time you tried moving a completed jigsaw puzzle from the kitchen table to a tray without breaking it."	Gareth Mitchell, Lecturer in Humanities, Imperial College London, talking on BBC Inside Science
hormone	spacecraft	"But they go and they act on receptors, so they effectively dock onto receptors, and then that process of docking on to a receptor triggers a chain reaction which then regulates the switching on of genes or the sending of signals inside a cell. So if you imagine, almost like a bit of a spacecraft or something travelling around a highway and then docking in at a certain position."	Sadaf Farooqi – Professor of Metabolism and Medicine at the University of Cambridge, speaking on an edition of BBC's In Our Time
hormone	orchestral conductor	"Our hormones are actually the conductors of an orchestra. They're effectively the system that pulls everything together and makes sure everything is acting in concert and at the right time."	Sadaf Farooqi – Professor of Metabolism and Medicine at the University of Cambridge, speaking on an edition of BBC's In Our Time
hormone	door key	"…the endocrine gland releases the hormone into the blood and that travels all the way around the body and every cell and tissue will see that hormone, but it only acts on a few of those tissues, or it might act on many of them, and the way that it does that is because the cells that respond to the hormone are effectively they express, they produce, the receptor that the hormone binds to. So I think a really good analogy to that might be the idea if you think of the hormone as a key, and you are walking down a street and there are all these doors with locks in it, and all of a sudden you keep trying the key in all the locks till you find the one that it fits and the door opens."	Andrew Bicknell – Associate Professor in the School of Biological Sciences at the University of Reading, speaking on an edition of BBC's In Our Time
immune response	PIN codes	"the immune system when it goes into an allergic response it has several, what are called, biological pathways. So, if you think of it like a PIN code, and you have ten numbers to fill out the PIN, your body can take thirty thousand different ways to go into an allergic reaction, which is why most of us do not have the same type of reaction, so you and I might be allergic to shellfish, but I might just get a mild upset stomach whereas you may end up in the emergency room with an anaphylactic event."	Theresa MacPhail, medical anthropologist, speaking on 'Start the Week'
'junk' D.N.A.	junk!	"Actually, junk D.N.A. is not a bad analogy, because junk is something that you put in the attic that you might want to use later."	Professor Anne Ferguson-Smith, Pro-Vice-Chancellor for Research and the Arthur Balfour Professor of Genetics at the University of Cambridge, interviewed on BBC's The Life Scientific'
LiFi (light based communication)	swimming in the ocean	"…the radio frequency spectrum is the resource where all these radio systems, 5G wifi and so on, work and that is a resource that is limited and it is not possible to indefinitely expand, so that's why it is absolutely natural and inevitable to look beyond the radio spectrum. If you go into a hotel in Summer in a warm place, the swimming pool is often crowded with people and you can't really swim the way you want, but visible light allows us to swim in the oceans and that is what LiFi will enable…"	Prof. Harald Haas, Distinguished Professor of Mobile Communications and Director of the Li-Fi Research and Development Centre at the University of Strathclyde, taling to Jim Al-Khalili on BBC's The Life Scientific
lithium treatment for bipolar disorder	lithium in batteries	"It's often struck me how strange it is that the active ingredient in a drug I took for my mental health was a silvery, white, metal. [It is actually a salt of lithium, not metal.] What was lithium doing to me? No one could answer me for certain. One theory was that it behaves in the brain like it does a battery. That whether dealing in electrons or neutrons [sic] lithium supplies constant and consistent power for all manner of electric devices, including the most complex one in the universe."	Laura Grace Simpkins, talking on BBC's Lights Out episode Lithified
metallic structure	choreography	So you know, if you look at ballet dancers, in Swan Lake for example, they move in a very systematic choreographed manner, a disciplined movement. And similarly, atoms, they can all move in the same direction at the same instant of time. And that has a different consequence to chaotic dancing, where people move in a haphazard manner. And similarly, atoms break all their bonds rearrange in a random way into a new pattern."	Professor Sir Harry Bhadeshia (Emeritus Tata Steel Professor of Metallurgy at the University of Cambridge; Professor of Metallurgy, Queen Mary University of London) interviewed on an episode of BBC's The Life Scientific
microbiome	'orchestral' signalling	"The microbiome has this capacity to signal from the mother to the developing baby, and we call that orchestral signalling. The microbiome has so many different molecular languages that it speaks, that you can think of it in terms of an orchestra with different bits of the band doing different bits of important signalling that educate the immune system or might help you metabolise food for example."	Dr James Kinross, Senior Lecturer in Colorectal Surgery and a Consultant Surgeon at Imperial College London, speaking on 'Start the Week'
microbiome	garden	"I like to think of the gut microbiome as a beautiful garden, which has all of the necessary elements to blossom into a diverse and colourful oasis. The food we eat forms the soil for our microbial garden. Specifically, so-called prebiotic foods. The fibres and other non-digestible components act as food for the microbiome, stimulating growth of our existing gut bacteria. The microbes themselves we can think of as seeds, which will only be able to thrive if the soil is ready and rich. A healthy, thriving microbial garden will then have flowers, leaves and lush grass, all releasing oxygen, water vapour, and other chemicals into the garden's micro-climate. … the food we eat is crucial for the success or failure of our internal garden."	Tim Spector Professor of Genetic Epidemiology at King's College London – serialisation of 'Food for Life' on BBC Radio 4
microbes	shift-workers	"Microbes, like us, need a good night's sleep. And if you give them that time to sleep, then they have a cleaning team that comes out at night, they have a shift change, so scavengers come tidying up your gut lining and make your gut this perfectly-oiled machine that our ancestors had but we've lost."	Tim Spector Professor of Genetic Epidemiology at King's College London speaking on BBC's Just One Thing – with Michael Mosley
mitochondria	car	MR: "So, exercise is a strong way to rejuvenate mitochondria. An analogy is parts in a car, for example, can develop rust, and those rusty parts needs to be removed, and then replaced. The same concept applies with mitochondria. Now where exercise fits in, is exercise stimulates both the removal of older mitochondria and the synthesis of new mitochondria." MM: "So, essentially you are clearing out the junk which makes space for newer better working engine parts."	Associate Professor Matt Robinson (Oregon State University) interviewed by Dr Michael Mosley on BBC's 'Stay Young'
neocortex	new storey built on a bungalow	"we are have two decision-making processes, the first one is earlier evolved one, the limbic system, we share that with most animals; and then you have this one called the pre-frontal cortex, the neocortex it means literally new bark and it kind of grew on top of this. I sometimes think of it as a second storey added to a bungalow. So, you have people in this bungalow, the limbics, and then they had trouble making their bank payments, so the bank of evolution said 'all right, we need somebody more responsible to help you, we're having neighbours move in above you', and they're the pre-frontals, and the pre-frontals will help the limbics make better choices."	Dr Piers Steel (Professor in the Organizational Behaviour and Human Resources / the Brookfield Research Chair at the Haskayne School of Business, University of Calgary)
pheremones	social media	"A dog going on a walk is using its nose to explore the changes in its world, the most important things in its environment, and also the cues left behind by other dogs, so it's really a lot like social media, right, it's a way of catching up with people you know who are not in your immediate vicinity."	Ed Yong (science journalist) interviewed on an episode of BBC Inside Science
pituitary gland	orchestral conductor	"we call the pituitary gland the conductor of the endocrine orchestra because it is really there, it's got a vital critical role in coordinating"	Rebecca Reynolds -analogyProfessor of Metabolic Medicine at the University of Edinburgh, speaking on an episode of BBC's In Our Time
ribcage	concertina	"…if you are part of amniote tetrapods, that's ourselves, and reptiles, and birds and so forth, you've got big hoopy ribs, that form a ribcage, and they've got a muscular, if you like, concertina around your chest which can expand and contract so you've got negative pressure in your lungs to fill them full of air…"	Prof. Michael Coates (Chair and Professor of Organismal Biology and Anatomy at the University of Chicago), 'In Our Time', 20 October 2022
sampling the ocean	insects collected on a windshield	"The plankton comes in through a hole in the front of the CPR [continuous plankton recorder], and it's filtered onto the silk, so you know if you are driving through a country road and you get insects splattered on your windscreen, it's a little bit like that when you look at a CPR sample under a microscope. So the plankton are in the water, the water hits the silk and the plankton are like splattered against the silk, you can see they are a bit broken and squashed…"	Abigail McQuatters-Gollop, Associate Professor of Marine Conservation at the University of Plymouth, talking on an episode of BBC In Our Time
seismometer	stethoscope	"A big nuclear explosion produces a lot of sound. Well the sound can propagate through rock, that's what produces the signals that we can observe a long ways away on a seismometer, which is an instrument, well you can think of it as a stethoscope, it's just listening to the ground…"	Prof. Thorne Lay (seismologist, Professor of Earth and Planetary Sciences, University of California Santa Cruz), (science journalist), 'Science in Action', 10 June 2019
serotonin	orchestral musician	"The idea that one neurotransmitter is solely responsible for depression, we have long moved on from that as researchers and mental health professionals in the field, as we were saying I think that serotonin does have a role to play in emotion and mood, and it may be important to some extent in depression, but it will be as one player in a rather complex orchestral piece, it is not doing a solo, and so it is really difficult to pull apart these different processes and their role in depression."	Prof. Catherine Harmer, Professor of Cognitive Neuroscience, University of Oxford, interviewed on BBC's 'Is Psychiatry working?'

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From science print journalism:

Topic	Analogy	Source
silk production	"Fibroin is a block co-polymer comprised of very long, highly hydrophobic chains joined together by short hydrophilic linkers. The protein is soluble in water inside the silkworm's silk gland. But as it leaves, it is forced through a cylindrical nozzle, which triggers it to self-assemble into a solid insoluble fibre. 'Silk is spun via a controlled protein denaturation,' says Holland. 'It's the equivalent of cooking an egg, but instead of using heat, you are using mechanical flow to cook the silk proteins and transform them from a hydrated state to a dehydrated and aggregated state.'"	Dr Chris Holland, Senior Lecturer in Natural Materials, University of Sheffield, quoted in Chemistry World

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Learner analogies

Topic/concept	Learner analogy	Source
energy	"Because, it's using a lot of our energy, doing something…thinking…like, when you haven't got any energy, you can't think, like the same as TV, when it hasn't got any energy, it can't work. So it's a bit like our brains, when we have not got enough energy we feel really tired, and we just want to go to sleep"	Jim Y7 student (read about Jim's ideas)
energy	"sleep, which can give us more energy, a bit like food…it's like putting a battery onto charge, probably, you go to sleep, and then you don't have to do anything, for a little while, and you, then you wake up and you feel – less tired"	Jim Y7 student (read about Jim's ideas)

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Scientific concepts as analogues for non-scientific targets

Scientific concept	Analogy	Source
acids	"What strikes me as objectionable in the postmodernist outlook, on the other hand, is its pervasive relativism, which attacks truth the way an acid eats up metal."	Wolfgang Smith {mathematician, physicist, philosopher of science}
chemical analysis	"The gradual separation of affine and projective geometry from metric may be compared with the procedure of the chemist, who isolates increasingly valuable constituents from a compound by using constantly stronger analytical reagents; our reagents are first affine and then projective transformations."	Christian Felix Klein, German mathemtician (quoted in translation)
chemical analysis	Hippolyte Adolphe Tain "coined the celebrated phrase that the historian must regard virtual and vice just as the chemist regards sugar and sulphuric acid, satisfied to decompose each into its elements without attaching any sort of moral judgement to his analysis."	Ernst Cassirer
chemical reaction	"I got jammed into a room with Will.I.Am, the rapper, who was talking about his views for AI, and suddenly you've got these activists standing next to somebody from some of the big tech. companies, and a government minister, and a group from Kenya, all talking about whether AI could actually be a tool to reduce social inequality, rather than increase it. So, it is a bit like a chemistry experiment where you take all of these ambitious, self-selecting, hustling molecules from around the world, shove them into one test-tube, apply maximum pressure, and force them to collide with each other at close quarters with no sleep, and see what kind of compounds arise."	Gillian Tett, journalist, talking about the World Economic Forum at Davos on BBC's The Week in Westminster (read about this analogy here)
chemistry	"Again and again [French historian, Numa Denis Fustel de Coulanges] warned against 'vague generalities' and premature synthesis. History, he said is not a rationalistic science, but a science of facts; it is a science of observation that may be compared to chemistry."	Ernst Cassirer
classification in biolo0gy	"In a way, learning how to speak a language resembles developing a botanical system of classification, because describing the world involves grouping similar things together and using related words to label them."	Patricia Fara Erasmus Darwin. Sex, science and serendipity
ecosystem	"If the world of research were an ecosystem, with scientists of different disciplines representing different species, then physicists would be classified as invaders. After all, they've spread their methods and tools to many other fields over the years, infiltrating not only other natural sciences but the social sciences too."	Marco Patriarca, Els Heinsalu and David Sánchez writing in Physics World
homeostasis	"Witchcraft accusations, expressing as they did only tensions between unrelated equals and rivals, are presented as a sort if all-purpose social device, at one and the same time restraining uncharitable behaviour (which might give rise to accusations) and – in apparent contradiction – bringing grudges harmlessly out into the open, A control system, in fact, with a negative feedback. Yet on Evans-Pritchard's own showing Zande society hardly displayed homeostasis at the time he was studying it."	Eva Gillies {interpreter and social anthropologist}
locomotion	"The operation of cognition is analogous to the physiology of movement, To move a limb, an entire so-called myostatic system must be immobilised to provide a basis of fixation. Every movement consists of two active processes; namely, motion and inhibition. The corresponding features in the operation of cognition are purposive, directed determination and cooperative abstraction, which complement one another."	Ludwik Fleck {1896 – 1961, biologist}
magnetism	Einstein 'acted on women as a magnet acts on iron filings'	Ascribed to an architect friend of Einstein
magnetism	"as soon as [Cristobal] Game had it, and rather like iron filings, England players gathered around him"	ITV commentary from England versus Chile in the 2023 Rugby (Union) World Cup
the microscope	"Produce the impressions or original sentiments, from which the [complex] ideas are copied. … They are not only placed in full light themselves, but may throw light on their correspondent ideas, which lie in obscurity. And by this means, we may, perhaps, attain a new microscope or species of optics, by which, in the moral sciences, the most minute, and most simple ideas may be so enlarged as to fall readily under our apprehension, and be equally known with the grossest and most sensible ideas, that can be the object of our enquiry."	David Hume
motion	"If the probability in question – a positive number less than unity – is allowed to take on the zero value, the refined concept of possibility is seen to subsume the concept of impossibility much as rest had been made a particular case of motion: just as 'rest' has ben identified with "zero velocity motion", so 'impossibility' is now identified with 'zero probability'."	Mario Bunge
organism	"An argument is like an organism. It has both a gross, anatomical structure and a finer, as-it-were physiological one…one can distinguish the main phases marking the progress of the argument from the initial statement of an unsettled problem to the final presentation of a conclusion. These main phases will each of them occupy some minutes or paragraphs, and represent the chief anatomical units of the argument – its 'organs'. so to speak. But within each paragraph, when one gets down to the level of the individual sentences, a finer structure can be recognised… It is at his physiological level that the idea of logical form has been introduced, and here that the validity of our arguments has ultimately to be established or refuted. …we cannot afford to forget what we have learned by our study of the grosser anatomy of arguments, for here as with organisms the detailed physiology proves most intelligible when expounded against a background of coarser anatomical distinctions. Physiological processes are interesting not least for the part they play in maintaining the function of the major organs in which they take place; and micro-arguments (as one may christen them) need to be looked at from time to time with one eye on the macro-arguments in which they figure…"	Stephen Toulmin {philosopher}
paeleontology	"One of the most important scientific services performed by Coulanges was the development of this hermeneutics. His achievement in La Cité antique may be likened to that of a palaeontologist who goes back to the older geological strata in order to acquire through their investigation a new insight into the world of living organisms."	Ernst Cassirer
practical challenges	"Historical, linguistic, psychological and many other problem kinds occupy both first-hand and second-hand philosophers, just as cytologists must often struggle with their electron microscopes, archaeologists with jeeps, and prehistorians with the geological evidence. Research into historical, linguistic, psychological and other problems may shed light on philosophical problems and are often propeaudeutic to them – but they are not philosophical problems."	Mario Bunge
skeleton	"Considered form this standpoint history becomes not only anthropology but anatomy. We might be sure of finding in it beneath all the diversity and variation of events, always the same more or less unalterable bony framework. Facts change but their skeleton remains. 'History today, like zoology, has discovered its anatomy…'."	Ernst Cassirer (and quoting Hippolyte Tain)
tectonic plates	"Like the different tectonic plates in the Earth's crust that tend to move in opposite directions, with occasionally disastrous results, the various elements making up the mind-set of the average person today do not form a harmonious whole."	Gerald Holton {physicist and hsitorian of science}
the telescope	"And I would add that there are in fact no other means by which the things of Paradise can be known: the purified mind constitutes the only 'telescope', the one 'scientific instrument' by which these things can be brought within range of human observation."	Wolfgang Smith {mathematician, physicist, philosopher of science}
wavelength	"…no purely physiological account could be an adequate description of an action. Obviously, it could not; even if the study of the agent's brain could give us all the information that we needed beyond the observation of his physical movement, we should still have to decode it. But this is not an objection to holding that actions can be explained in these terms, any more than the fact that to talk about wave-lengths is not to describe colours is an objection to the science of optics."	A. J. Ayer {philosopher}

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Analogies between scientific ideas

Topic	analogy	source of analogy
biology	"In this sense the organismic conception is a prerequisite for the transition of biology from the stage of natural history, i.e., description of forms and processes in the organism, to an exact science, it seems to be the task which is set to our age, to accomplish in biology that "Copernican revolution" which in the sciences concerned with inanimate matter, took place with the transition from the Aristotelian world-system to modern physics."	Ludwig von Bertalanffy
biology	"threads of the [spider's] web are spun so finely that a fly's eye with its crude visual elements cannot spot the web and the fly flies without warning to its doom, just as we, completely off guard, drink water which contains cholera bacilli invisible to our eye."	Jakob von Uexküll
comets	"…Kepler's thoughts: his chief analogy for a comet was a rocket, which ignites, accelerates and then slows down, while travelling in a straight line."	Johannes Kepler (reported in Nigel Calder The Comet is Coming! The feverish legacy of Mr Halley)
development of scientific ideas	"But if we may borrow a hypothesis from the prehistory of palaeontology, a proto-idea [such as the Ancient Greek ideas of the atom or of the elements] must not be construed as a 'freak of nature'. Proto-ideas must be regarded as developmental rudiments of modern theories…Any absolute criterion of judgement as to suitability is as invalid for fossilised theories as a chronologically independent criterion would be for adaptability of some palaeontological species. The brontosaurus was as suitably organised for its environment as the modern lizard is for its own. If considered outside its proper environmental context, however it could not be called either 'adapted' or 'unadapted'. The development of thought proceeds so much more rapidly than the pace appropriate to palaeontology that we continuously witness the occurrence if 'mutations' in thought style. The transformation in physics and in its thought style brought about by relativity theory represents such a mutation, as does the adjustment in bacteriology resulting from the theories of variability and cyclogeny."	Ludwik Fleck {1896 – 1961, biologist}
evolution	"…Wallace had had a psychedelic experience following a malaria attack and had written back to Darwin his insight that the principle of natural selection was like the operation of steam engine with a governor…"	Alfred Russel Wallace (1823 – 1913, naturalist, co-discoverer of evolution by natural selection)
geology	"means of transport are for the geologist what telescopes are for the astronomer"	Jean-Baptiste Armand Louis Léonce Élie de Beaumont {1798-1874, geologist}
geometry	"Conchois, or Conchylis-a most beautiful and picturesque curve; it bears a fanciful resemblance to a conch shell. The conchois is capable of infinite extension, and presents a striking analogy between the animal and mathematical creation – every individual of this species containing within itself a series of young conchoids for several generations, in the same manner as the Aphides and other insect tribes are observed to do."	The Loves of the triangles (footnote to satirical poem, first published 1798)
histamine signalling	"So, histamine is just a compound that cells use to signal each other when they are damaged or something is wrong. And so once one cell triggers, it's a bit like we've all seen that nuclear reaction example with the ping-pong balls, that's a bit what it's like with histamine. So, once one ping-pong ball goes off, the cells next to it get the signal that something is wrong, also release histamine."	Theresa MacPhail, medical anthropologist, speaking on 'Start the Week'
integration in science	"As the blood in nourishing the body separates into countless capillaries, only to be collected again and to meet in the heart, so in the science of the future all the rills of knowledge will gather more and more into a common and undivided stream."	Ernst Mach (1838 – 1916, physicist and philosopher)
light and sound	"I discovered so great a mutual affinity between the two [Optics and Acoustics] that I have concluded that light is nothing other than a certain consono-dissonance for the eyes, while sound… is a certain shadow-light for the ears."	Athanasius Kircher quoted by John Glassie
light and sound	"an analogy subsisting between sound and light has been gradually traced into a closeness of agreement, which can hardly leave any reasonable doubt of their ultimate coincidence in one common phenomenon, the vibratory motion of an elastic medium."	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
mathematics	"As Galileo first truly understood, experiment and observation form the acid test of theory and distinguish useless form useful mathematical language."	David Lindley – The Dream Universe. How fundamental physics lost its way
measurement	[Explaining why he was measuring temperature to "fractions of a thousandth of a degree"] "Suppose I had a lens, and I told you what I was doing is I was polishing it, so I could get a sharper image, no one would even question, they would say it is obvious why you are doing that, because you don't know what you are going to see until you have made it and then you reveal new detail, new nuances. Well, actually, all physical measurements are like that. So, when you learn to measure the temperature properly instead of things appearing blurry you see fine distinctions. So, it's like we're sharpening a kind of thermal lens of what could possibly be seen in the world."	Michael de Podesta, physicist (interviewed on the Nature Podcast)
mutation	"…spontaneous so-called constitutional process within the genotypes, such as mutations and spontaneous gene changes, roughly comparable with spontaneous radioactive phenomena within an atom."	Ludwik Fleck {1896 – 1961, physician and biologist}
natural selection	"Haeckel liked to compare Darwin's reform of biology with the reform of cosmology achieved by Copernicus three hundred years earlier. He thought one of its chief virtues was that it removed the last traces of anthropomorphism form science and provided it with a really universal point of view. Here emphasis was place not so much on the content of the doctrine, some particular theorem, as on the fact that it changed biology's whole frame of reference."	Ernst Cassirer
perception	"Let us call one of these aggregates of sensations an element. That will be something analogous to the point of the mathematicians; it will not be altogether the same thing however. We can not say our element is without extension, since we cannot distinguish it from neighbouring elements and it is thus surrounded by a sort of haze. If the astronomical comparison may be allowed, our 'elements' would be like nebulae, whereas the mathematical points would be like stars."	Henri Poincaré {1854 -1912, mathematician, physicist and philosopher}
phrenology	"To me, Phrenology appears to bear the same relation to the doctrine of even the most recent metaphysicians [as does] Copernican astronomy bears to the system of Ptolemy."	Robert Chalmers {1802-1871, writer}
phrenology	"Only a few years ago we had but four elementary substances in nature…Now there are proved to be compounds; and we have almost sixty elementary substances. So also, by the new and interesting science of phrenology, instead of four original powers, as perceptions, memory, judgement, and volition, we have no less than thirty-five powers or faculties, that is distinct organs, clearly marked out in every commonly well organized [sic] human brain."	From an 1826 speech reported by the London Co-operative Society's magazine
psychology	"In several respects the notion of a collective unconscious is the counterpart, in social psychology, of the notion of memory traces in individual or general psychology. Both appear to assume that psychological material – images, symbols, ideas, formulae – are somehow individually preserved and stored up for use, either in the central nervous system of the individual , or somewhere in a persistent psychological structure which is the possession of a social group."	Frederic C. Bartlett
Rorschach projective personality test	"If the Rorschach was an X-ray, the hidden but all-important personality was the invisible skeleton people wanted to see, and projection was what made it visible." … "The Rorschach 'seemed like a mental X-ray machine', recalled a graduate student at the time. 'You could solve a person by showing them a picture'."… "The Rorschach was an X-ray, the test that couldn't be faked any more than a slide could fool a slide projector."	Damion Searls, The Inkblots. Hermann Rorschach, his iconic test & the power of seeing
semantic closure of theories	"The condition of semantic closure does not prohibit the exportation [ital] of concepts introduced by a given theory: the closure, like a semipermeable membrane, works only one way, to prevent the entry of new concepts once the theory has been formulated, in order to preclude an endless readjustment of the theory either to the data or to some philosophical tenet."	Mario Bunge {physicist and philosopher of science}
science methodology	"Moreover, as in chemistry we are sometimes compelled to acknowledge the existence of elements different from those already identified and known, though we cannot insulate them, and to perceive that substances have the characters of compounds, and must therefore be susceptible of analysis, though we do not see how it is to be set about; so, in physics, we may perceive the complexity of a phenomenon, without being able to perform its analysis… But, it will now be asked, how we are to proceed to analyse a composite phenomenon into simpler ones, and whether any general rules can be given for this important process? We answer, None; any more than (to pursue the illustration we have already had recourse to) general rules can be laid down by the chemist for the analysis of substances of which all the ingredients are unknown."	Sir John Frederick William Herschel, {1792 – 1871, polymath scientist}
visualisations of atoms	"As the theory gained support in chemistry and physics, however, scientists came to regard atoms as familiar things. When speaking strictly they renounced the picturable atom; but why speak so strictly? The geometer never denies himself the use of drawn lines: lines should be one-dimensional, but proofs and constructions cannot be carried out with one-dimensional lines. Similarly, physicists could think about atoms only by visualising them. Why not? It helped to secure explanations."	Norwood Russell Hanson {1924 – 1967, philosopher of science}
water cycle	"Steam rises from the ocean, floats in clouds, descends in rain and dew, or is condensed on hills, produces springs, and rivers, and returns to the sea. So the blood circulates through the body and returns to the heart"	Erasmus Darwin {1731 -1802, physician and poet}

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Analogy as a scientific tool

Although most of the examples discussed on this site concern the use of analogy in teaching/communicating science, analogy has been used by scientists as a thinking tool, as a source of hypotheses to suggest relationships in a target domain by analogy with a well understood system.

topic	comparison	source
atoms	"The theory in question was the vortex model of the atom, due in part to Lord Kelvin and prompted by his seeing some clever experiments on the properties of smoke rings, in which they vibrated and gently bounced off one another. Kelvin proposed that atoms were similar formations in the ether, the hypothetical medium that was supposed at the time to carry light and other forms of electromagnetic radiation."	David Lindley – The Dream Universe. How fundamental physics lost its way
electromagnetic waves	"It was already well accepted that there was an optical ether that carried light waves. In an analogy to sound waves, which can only exist in air [or other elastic material medium], scientists concluded that there must be some medium that supported light waves as well."	Matthew Stanley: Einstein's War. How relativity triumphed amid the vicious nationalism of World War 1
heat	"Carnot imagined heat flowing through a steam engine in somewhat the same way that water flows through a water mill. Water, flowing downhill, transfers some of its energy to the mill wheel. Similarly, heat, flowing from high temperature to low, causes a piston to move. Although this analogy was wrong, Carnot came to some correct conclusions, most notably that it impossible to turn all the heat into mechanical motion."	David Lindley – The Dream Universe. How fundamental physics lost its way
refraction	"Al-Farisi…used a hollow glass sphere filled with water as an analogue for a raindrop. His studies led him to conclude that the rainbow is due to a combination of refraction and internal reflection of sunlight in the individual drops of water suspended in the air after a rainfall."	John Freely – Light from the East. How the science of medieval Islam helped to shape the Western World.

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Note on analogies, similes and metaphors.

In practice the precise demarcations between similes, metaphors (and anthropomorphisms) and analogies may not be absolutely clear. I have tried to follow the rule that if a comparison is set out to make a structural mapping clear (even if this is not spelt out as a mapping: e.g., an atom with its electrons is like a sun with its planets) this counts as an analogy. Where I do not think a comparison is an analogy, but the comparison is made explicit ("…as if…", "…like…": e.g., the atom, like a tiny solar system) I consider this a simile. When the audience is left to spot a comparison (rather than a literal identity) is being made (e.g., the oxygen atom, this tiny solar system) I class this a metaphor.

Anthropomorphism may be seen as a particular kind of metaphor where a metaphorical feature implies a non-human entity has human attributes (e.g., meteors can be impetuous).

I reserve the right to reassign some of these comparisons in due course!

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Work cited:

• Taber, K. S. (2013). Upper Secondary Students' Understanding of the Basic Physical Interactions in Analogous Atomic and Solar Systems. Research in Science Education, 43(4), 1377-1406. doi:10.1007/s11165-012-9312-3 [Download this article]

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