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In Aristotelian physics there is the concept of natural motion (when there are no forces, just gravity), differing from so-called violent (enforced) motion. From my cursory knowledge of general relativity there seems to be an obvious similarity to how motion under gravity is conceptualized there, i.e. not as a result of a gravitational force acting but as a body moving along the spacetime curvature – "naturally".

But how should we interpret this? Aristotle wrote a lot, and so it seems not surprising that he may have gotten lucky, saying something modern science would finally support. Do we have evidence that he had certain correct insights to believe that gravity is different from the other "forces"? Or was it just luck?

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  • It is a very feeble analogy: for A gravity is not a force (i.e. a reciprocal action between matter), correct, but it is neither an action of space on matter. The bodies are heavy and light, just as they are hot and cold. Every body as a "preferred" natural place: its "home" and it strives to "go home". This is a consequence of the intrinsec order of the cosmos.
    – Mauro ALLEGRANZA
    Mar 5, 2017 at 19:35
  • @MauroALLEGRANZA it seems I'm not alone seeing this connection.
    – viuser
    Mar 5, 2017 at 21:50
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    cf. "Aristotle's Aether and Contemporary Science" by Christopher A. Decaen, which mentions the theory of General Relativity
    – Geremia
    Mar 9, 2017 at 16:04
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    This historical background of the metamorphosis of Aristotelian physics into physics in the modern sense might also help.
    – Geremia
    Mar 9, 2017 at 16:09
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    Rovelli points out that some structural features of Aristotelian physics reappear in Newton's Principia, and perhaps deliberately. The distinction between natural and violent motions is paralleled by the one between uniform and accelerated (under action of a force) motion. See his Aristotle's Physics: a Physicist's Look. But the contexts of Aristotle's physics and GR are so vastly different that the "naturalities" have little in common beyond the name.
    – Conifold
    Mar 10, 2017 at 1:37

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Do we have evidence that Aristotle had certain correct insights to believe that gravity is different from the other "forces"?

Well, what else could he think? That is, what other enduring, permanent physical forces are there, anyway? In modern terms, there are just four fundamental physical forces: gravity, electromagnetic, strong nuclear, weak nuclear. Of these, Aristotle could have been familiar only with gravity. The other three fundamental forces were unfamiliar to Aristotle (I don't know whether he was familiar with phenomena of magnetism and / or static electricity). Aristotle also rejected the contemporary atomic theory, which was probably closer to modern physics than Aristotle's. Those three other fundamental physical forces were not discovered for another 2000 years.

Additionally, beside the downward movement, which today we identity as gravity, Aristotle also believed that the upward movement of fire and hot air was also a fundamental natural movement. Today we view the upward movement as more complex, less fundamental than the downward movement. The upward movement involves air density and air pressure, in addition to an indirect influence of gravity (colder air sinking downwards).

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  • There are lot of "forces" in A's universe : a man working with a lever, a man pushing a table on the floor, a man rowing on a boat...The question above (and similar) relies on the "error" of mixing historical interpretations with scientific comparison. If we "compare" A's physical theory with e.g. Newtonian one, from the point of view of modern scientific approach, A's theory (and Aquinas and Descartes) is simply wrong, period. Reason : it makes wrong predictions of natural facts.
    – Mauro ALLEGRANZA
    Mar 15, 2017 at 10:50
  • If we read with "historical insights" we have to consider that A's concept of force is not the post-Newtonian one. A was not interested to mathematical laws describing and predicting facts, but to understanding natural facts, i.e. explaining them in terms of causes.
    – Mauro ALLEGRANZA
    Mar 15, 2017 at 10:51
  • From this second point of view, to ask if we can "read" some hints of geenral relativity into A's text, is simply useless. General relativity is "conceivable" only on top of Newtonian physics and Maxwell electromagnetism.
    – Mauro ALLEGRANZA
    Mar 15, 2017 at 10:53
  • Having said that, for me your answer is "formally" correct :-)
    – Mauro ALLEGRANZA
    Mar 15, 2017 at 10:54
  • @MauroALLEGRANZA Thanks for the "formal" correctness, whatever that means :). I'm not sure though how your comments relate specifically to my answer. For one thing, I emphasized the unique permanent, enduring character of the force of gravity.
    – Ram Tobolski
    Mar 15, 2017 at 19:09
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You're a little confused about what is meant by natural motion here. It means motion without the presence of any forces, including gravity.

It's easy enough to see that there are three possible natural motions of an object

  • in a straight line, because which direction should it choose to move in?

  • In a wave, because it moves in all directions at once

  • Randomly, as it chooses a direction, moves, chooses another direction, and moves.

All three of these motions were theorised by philosophers then. Anaximenes on wave motion, Aristotle on straight line motion, and Democritus on random motion - aka the clinamen.

As for your suggestion that maybe Aristotle 'got lucky', perhaps you could explain why Newton is known to have written in his notebooks:

Plato is my friend, Aristotle is my friend, but truth is my greater friend?

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