Perhaps Poincaré was reflecting how two opposing schools of philosophical thought had disagreed on wherever the primary source of human knowledge was experience (the empiricists) or pure reasoning (the rationalists), but elsewhere in the same text Poincairé (1902/1913/2015) dismisses the idea that the laws of physics can be obtained by simple reflection on human intuitions. Such intuitions can lead us astray.
If he is being consistent then, surely "the contrary hypothesis is [only] singularly repugnant to the mind" because "the commonest experience confirms…the principle of relative motion". That is, suggestions that are clearly contrary to our common experience – such as, perhaps, the earth is moving? – are readily rejected as being nonsensical and ridiculous.
If that is so, then Poincaré was not really offering two independent lines of argument as his second reason was dependent upon his first.
This put me in mind of some comments of Kryten, a character in the sci-fi series 'Red Drawf',
{responding to a crew suggestion "Why don't we drop the defensive shields?"}
"A superlative suggestion, sir, with just two minor flaws.
One, we don't have any defensive shields, and
two, we don't have any defensive shields.
Now I realise that, technically speaking, that's only one flaw but I thought it was such a big one it was worth mentioning twice."
Kryten (mechanoid assigned to the mining spaceship Red Dwarf)
or alternatively,
{responding to the crew suggestion "I got it! We laser our way through [the 53 doors from here to the science deck]!"}
Ah, an excellent plan, sir, with only two minor drawbacks.
One, we don't have a power source for the lasers; and
two, we don't have any lasers.
Kryten
French physicist Poincaré'Red Dwarf' character, Kryten
The principle of relative motion
What Poincairé meant by 'the principle of relative motion' was that
"The motion of any system must obey the same laws, whether it be referred to fixed axes, or to moveable axes carried along in a rectilinear and uniform motion."
the principle of relative motion
In other words, imagine a train passing a station at 10 ms-1, in which a naughty physics student throws a pencil eraser of mass m with a force of F at another passenger sitting in front on him; while a model physics student observes this from the stationary station [sic] platform.
The student on the train would consider the eraser to be at rest before being thrown, and can explore its motion by taking u=0 ms-1 and applying some laws summarised by
F=ma,
v=u+at,
v2=u2+2as,
s=ut +1/2at2…
From the frame or reference of someone in the the station it is the train that moves, (Image by StockSnap from Pixabay) but……From the frame of reference of the train (or tram), it seems to be the rest of the world that is moving past (Image by Pasi Mämmelä from Pixabay)
The student on the platform would observe the eraser to initially be moving at 10 ms-1, but could calculate what would happen using the same set of equations, but taking u=10 ms-1
Any values of v calculated would be consistent across the two frames (when allowing for the 10 ms-1 discrepancy) and other values calculated (s, t) would be the same.
This reflects the relativity principle of Galileo which suggests that there is no absolute way of determining whether a body is moving at constant velocity or stationary: rather what appears to be the case depends on one's frame of reference.
We might think that obviously it is the platform which is really stationary, as our intuition is that the earth under our feet is stationary ground. Surely we could tell if the ground moves?
We can directly feel acceleration, and we can sometimes feel the resistance to motion (the air on our face if we cycle, even at a constant velocity), but the idea that we can directly tell whether or not we are moving is an alternative conception.
For centuries the idea of a moving earth was largely considered ridiculous as experience clearly indicated otherwise. But if someone was kidnapped whilst asleep (please note, this would be illegal and is not being encouraged) and awoke in a carriage that had been set up to look like a hotel bedroom, on a train moving with constant velocity, they would not feel they were in motion. Indeed anyone who as travelled on a train at night when nothing is visible outside the carriage might well have experienced the impression that the train is stationary whilst it moves at a steady rate.
Science has shown us that there are good reasons to think that the earth is spinning, and orbiting the sun, as part of the solar system which moves through the galaxy, so who is to say what is really stationary? We cannot tell (and the question may be meaningless).
Who is to say what is moving – we can only make relative judgements? (Image by Drajt from Pixabay)
Source cited:
Poincaré, H. (1902/1913/2015). Science and Hypothesis (G. B. Halstead, Trans.). In The Foundations of Science. Cambridge University Press. {I give three dates because Poincaré published his book in French in 1902, and it was later published in an English translation in 1913, but I have a 2015 edition.}
I recently read a book of essays by Edward Rosen (1995) who (as described by his publisher) was "the editor and translator of Copernicus' complete works, was the leading authority on this most celebrated of Renaissance scientists". Copernicus is indeed, rightly, highly celebrated (for reasons I summarise below *).
The book was edited by Rosen's collaborator, Erna Hilfstein 1, and although the book was an anthology of reprinted journal articles, none of the chapters (articles) had abstracts. This reflects different disciplinary norms. In the natural and social sciences most journals requireabstracts – and some even offer a menu of what should be included – but abstracts are not always expected in humanities disciplines.
A collection of published papers from various journals – all lacking abstracts
It is not unusual for an academic book to be a compilation of published articles – especially when anthologising a single scholar's work. I was a little surprised to find the different chapters in the same book having different formats and typefaces – it had been decided to reproduce the articles as they had originally appeared in a range of journals (perhaps for authenticity – or perhaps to avoid the costs of new typesetting?)
But it was the absence of article abstractsthat most felt odd. The potential reader is given a title, but otherwise little idea of the scope of an article before reading. Perhaps it was my awareness of this 'omission' that led me to thinking that for a number of the chapters it would be possible to offer a very minimal abstract (an acute abstract?) that would do the job! Certainly, for some of these chapters, I thought a sentence each might do.
That is not to dismiss the scholarship that has gone into developing the arguments, but Rosen often wrote on a very specific historical point, set out pertinent ideas from previous scholarship, and then argued for a clear position contrary to some earlier scholars.
Copernicus has often been described as a priest, but Copernicus was never ordained a priest.
Copernicus was a canon in the Roman Catholic church, but this made him an administrator (and he also acted as physician), but he never became a monk or a priest.
It has been claimed that Copernicus misused the term axioms in his work, but his use was perfectly in line with authorities
Today axioms are usually expected to be the self-evident starting points for developing a deductive argument, but Aristotle's definition of axioms did not require them to seem self-evident.
It has been suggested that Calvin was highly critical of Copernicus, but it seems unlikely Calvin had ever heard of him
While Calvin's writing strongly suggest he was committed to a stationary earth and a sun that moved around the earth, there is no evidence he had specifically come across Copernicus.
A manifold chapter
Having noticed how so many of Rosen's articles took one claim or historically contentious idea and developed it in the light of various sources to come to a position, I was a little surprised when I reached Chapter 20, 'Galileo's misstatements about Copernicus', to find that Rosen was dealing with 5 distinct (if related) points at once – several of which he had elsewhere made the unitary focus of an article.
Rather than write my own abstract, I could here suggest a couplet of sentences from the text might have done the job,
"According to Galileo, (1) Copernicus was a priest; (2) he was called to Rome; (3) he wrote the Revolutions by order of the pope; (4) his book was never adversely criticised; (5) it was the basis of the Gregorian calendar. Actually, Copernicus was not a priest; he was not called to Rome; he did not write the Revolutions by order of the pope; the book received much adverse criticism, particularly on the ground that it contradicted the Bible; it was not the basis of the Gregorian calendar."
Rosen, 1958/1995, pp.203-204
I noticed that this was the earliest of Rosen's writings that had been included in the compilation – perhaps he had decided to dispense his ideas more sparingly after this paper?
Actually, there's a lot to be said for abstracts that pithily précise the key point of an article, a kind of tag-line perhaps, acting for a reader as an aide-mémoire (useful at least for readers like me who commonly stare at rows of books thinking 'I read something interesting about this, somewhere here…'). I have also read a lot of abstracts in research journals that would benefit from their own (further) abstracts, so perhaps such acute abstraction might catch on?
* Appendix: A scientific giant
Copernicus is indeed 'celebrated', being seen as one of the scientific greats who helped establish modern ways of thinking about the world – part of what is often perceived as a chain that goes Copernicus – Kelper – Galileo – Newton.
Copernicus is most famous for his book known in English as 'On the Revolutions of the Heavenly Spheres', or just 'Revolutions'. The key point of note is that at a time when it was almost universally agreed that the earth was stationary at the centre of 'the world', i.e., the cosmos, and that everything else revolved around the earth, Copernicus proposed a system that put the sun at the centre and had the earth moving around the sun.
The geocentric model of the cosmos was widely accepted for many centuries (Image by OpenClipart-Vectors from Pixabay)
From our modern worldview, it is difficult to imagine just how, well yes, revolutionary, that move was (even if Copernicus only moved the centre of the universe from earth to the sun, so our solar system still had a very special status in his system). This is clear from how long it took the new view to become the accepted position, and the opposition it attracted. Newton later realised that strictly the centre of revolution was the centre of mass of the solar system not the sun per se. 2
One problem was that there was no absolute observational test to distinguish between the two models and there were well-established reasons to accept the conventional geocentric model (e.g., we do not feel the earth move, or a great wind as it spins beneath its atmosphere; as the most dense element earth would naturally fall to the centre of the world, beneath water, air, fire, and the ether that filled the heavens {although the Earth was not considered a pure form of the element earth, it was earthy, considered mostly earth in composition 3}; and scriptures, if given a literal interpretation, seemed to suggest the earth was fixed and the sun moved.)
Copernicus' model certainly had some advantages. If the earth is still, the distant sphere with all the fixed stars must be moving about it at an incredible rate of rotation. But if the earth spun on its axis, this stellar motion was just an illusion. 4 Moreover, if everything revolves around the earth, some of the planets behave very oddly, first moving one way, then slowing down to reverse direction ('retrograde' motion), before again heading off in their original sense. But, if the planets are orbiting the sun along with the earth (now itself seen as a planet) but at different rates then this motion can be explained as an optical illusion – "these phenomena…happen on account of the single motion of the earth" – the planets only seem to loop because of the motion of the earth.
Despite this clear improvement, Copernicus model did not entirely simplify the system as Copernicus retained the consensus view that the planets moved in circles: the planets' "motions are circular or compounded of several circles,…since only the circle can bring back the past". With such an assumption the observational data can only be made to fit (either to the heliocentric model or its geocentric alternative) by having a complex series of circles rather than one circle per planet. Today when we call the night sky 'the heavens', we are using the term without implying any supernatural association – but the space beyond the moon was once literally considered as heaven. In heaven everything is perfect, and the perfect shape is a circle.
It was only when Kepler later struggled to match the best observational data available (from his employer Tycho Brahe's observatory) to the Copernican model that, after a number of false starts, he decided to see if ellipses would fit – and he discovered how the system could be described in terms of planets each following a single elliptical path that almost repeated indefinitely.
A well-known story is how by the time Copernicus had finished his work and decided to get it printed he was near the end of his life, and he was supposedly only shown a printed copy brought from the printer as he lay on his deathbed (in 1543). In the printed copy of the book an anonymous foreword/preface 5 had been inserted to the effect that readers should consider the model proposed as a useful calculating system for following the paths of heavenly bodies, and not as a proposal for how the world actually was.
Despite this, the book was later added to the Roman Catholic Church's index of banned works awaiting correction. This only occurred much later – in 1616, after Galileo taught that Copernicus' system did describe the actual 'world system'. But, in the text itself Copernicus is clear that he is suggesting a model for how the world is – "to the best of my ability I have discussed the earth's revolution around the sun" – not just a scheme for calculating purposes. Indeed, he goes as far to suggest that where he uses language implying the sun moves this is only to be taken as adopting the everyday way of talking reflecting appearances (we say 'the sun rises'). For Copernicus, it was the earth, not the sun, that moved.
Sources cited:
Copernicus, N. (1543/1978). On the Revolutions of the Heavenly Spheres (E. Rosen, Trans.). Prometheus Books.
Rosen, E. (1995). Copernicus and his successors (E. Hilfstein, Ed.). The Hambledon Press.
An article in the Jewish Standard reports how Erna's daughter undertook a charity bike ride "from Auschwitz-Birkenau, the Nazi-run death camp in the verdant Polish countryside, to the" Jewish Community Centre of Krakow (the town where her parents lived before being deported by the Nazis).
2 Newton also wrote as if the solar system was the centre of the cosmos, but of course the solar system is itself moving around the galaxy, which is moving away from most other galaxies…
3 These are not the chemical elements recognised today, of course, but were considered the elements for many centuries. Even today, people sometimes refer to the air and water as 'the elements.'
4 Traditionally, the 'heavenly spheres' were not the bodies such as planets, moons and stars but a set of eight conjectured concentric crystalline spheres that supposedly rotated around the earth carrying the distant stars, Saturn, Jupiter, Mars, the Sun, the Moon, Venus and Mercury.
5 A preface is written by the author of a book. A foreword is written by someone else for the author (perhaps saying how wonderful the author and the work are). Technically then this was a foreword, BUT because it was not signed, it would appear to be a preface – something written by Copernicus himself. Perhaps the foreword did actually protect the book from being banned as, until Galileo made it a matter of very public debate, it is likely only other astronomers had actually scrutinised the long and very technical text in any detail!
