An example of analogy in science:
"Thus we see that the nuclei of carbon and nitrogen in our circular reaction chain are forever being regenerated, and act only as catalysts, as chemists would say…we may therefore describe the whole process as the transformation of hydrogen into helium as induced by high temperatures and aided by the catalytic action of carbon and nitrogen.
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Since all other possible reactions lead to results inconsistent with the astrophysical evidence, it should be definitely accepted that the carbon-nitrogen cycle represents the process mainly responsible for solar energy generation.
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In view of the basic part played in this process by carbon, there is something to be said after all for the primitive view that the Sun's heat came from coal; only we now know that the 'coal', instead of being a real fuel, plays the role of the legendary phoenix."
George Gamow (1961) One, Two, Three…Infinity. Facts and speculations of science, Revised Edition, Dover Publications, Inc., New York.
Here the notion of a catalyst as a substance that is involved in, but not used up in, a chemical reaction is extended (by analogy) to nuclear reactions for a nuclide that is involved in, but not used up in, a nuclear process.
Read about analogy in science
Read examples of scientific analogies
The passage describes a theoretical mechanism by which nuclear fusions (and so energy release) can take place within the Sun. It s now believed that this process takes place in heavier stars but that within our Sun a different mechanism is the primary means of fusion/energy release. Gamow's argument that all other feasible mechanisms were inconsistent with the evidence, and therefore the carbon-nitrogen cycle should be definitely accepted proved to be misjudged.
Strictly, scientific claims are seem as provisional in the sense that they are always open to being revisited in the light of new evidence or new ways of thinking about the evidence. Scientific observations usually rely on technical apparatus and so depend on instruments being well-calibrated and working according to the assumed theory. It is always possible to find alternative explanations for any data set (even if this sometimes stretches credibility). Rhetoric which refers to absolutely certain knowledge, or proof beyond doubt, is inconsistent with our understanding of the nature of science.
Read about claims of scientific certainty
The idea that the Sun was an enormous ball of burning coal was once taken seriously by scientists (before nuclear processes were known) but would now be considered an alternative conception.
Read about the nature of alternative conceptions
Read about some examples of science misconceptions
Read about historical scientific conceptions
Gamow reference to the 'coal' (actually carbon nuclides) playing the role of the Phoenix is not a normal metaphor as the reader would not make sense of it without knowing about the legend of the bird that would burst into flames, and then reappear resurrected from its own ashes. This may therefore be seen as using a form of idiom.
Read about communicating science through idioms