# Locality and rigid bodies?

I know historically Newton's law of gravity was considered a joke due to locality issues (amongst the French).

Has there been a metaphysical analysis about rigid bodies also having locality issues?

I would be up for that read.

• How much of Einstein's relativity have you studied? That determines the level at which you can comprehend the answer. Apr 21, 2023 at 12:19
• It wasn't "considered a joke"; it was viewed as being in need of further explanation. The Cartesians didn't have any problems with the law of gravity itself; they merely claimed that there must be some way to explain gravity that didn't rely on action at a distance. Apr 21, 2023 at 14:12
• Is it possible that metaphysics is mum about this, just because of its speculative rather than observational nature, it didn't "see the problem of locality coming"? Apr 21, 2023 at 14:48
• @BobaFit i have 2 masters in physics :p but you can demonstrate the non locality in mere classical mechanics without sr or gr. Apr 21, 2023 at 14:49
• Cartesians did subscribe to Aristotelian "a thing cannot act where it is not" for matter, but I do not think rigidity was connected to locality/action-at-a-distance until it caused paradoxes in relativity. Descartes did consider most material bodies to be non-rigid, but not for reasons of locality (and he called "rigid" what is now called elastic, and "perfectly solid" what is now called rigid), see Slowik, Perfect Solidity: Natural Laws and the Problem of Matter in Descartes' Universe. Apr 21, 2023 at 17:34

'A joke'.. Newton himself was uncomfortable with action-at-a-distance.

“But hitherto I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses. For whatever is not deduc’d from the phaenomena, is to be called an hypothesis; and hypotheses, whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy.” -from The General Scholium to Principia mathematica

"It is inconceivable that inanimate Matter should, without the Mediation of something else, which is not material, operate upon, and affect other matter without mutual Contact…That Gravity should be innate, inherent and essential to Matter, so that one body may act upon another at a distance thro' a Vacuum, without the Mediation of any thing else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it. Gravity must be caused by an Agent acting constantly according to certain laws; but whether this Agent be material or immaterial, I have left to the Consideration of my readers."

—Isaac Newton, Letters to Bentley, 1692/3

The rigidness of Rigid Bodies is like the idealness of Ideal Gases - they are 'spherical cows in a vacuum', as we find from Deep Inelastic Scattering. Are you questioning how change propagates over the distances inside rigid bodies?

Perhaps the relevant topic is Mach's Principle, how rotating objects, such as gyroscopes and spinning celestial bodies, maintain a frame of reference. Sometimes stated as "local physical laws are determined by the large-scale structure of the universe". Is that a true parallel? Local properties like inertia rely on the universe as a whole.

• Newton wasn't uncomfortable with action at a distance, but those passages are quoted out of context since Mill, see Henry, Gravity and De gravitatione: the development of Newton’s ideas on action at a distance:"Given the very clear, and fairly numerous, statements in which Newton shows that he did believe in action at a distance... it should be blindingly obvious that this single passage has been, and continues to be misinterpreted." Apr 21, 2023 at 17:18
• The OP is not wrong about the "joke", it was an Aristotelian dogma retained by Cartesians:"Rather more than a century and a half ago it was a scientific maxim, disputed by no one, and which no one deemed to require any proof, that “a thing cannot act where it is not.” With this weapon the Cartesians waged a formidable war against the theory of gravitation, which, according to them, involving so obvious an absurdity, must be rejected in limine", ibid. Apr 21, 2023 at 17:36
• @Conifold: The first quote is one of his most famous statements on the issue. The second clearly states his discomfort, which as I understand it was pretty much universally shared in the scientific community. I don't see how you can deny that. The point I see him as making is that he was uneasy about the issue, & he was pointing towards more experiments being needed. He believed his theory worked, of course, that's not in question. No action-at-a-distance was not just a dogma, but an important hypothesis still of lasting significance in the movement towards physicalist-materialism. Apr 21, 2023 at 19:42
• You should read the linked paper. The "fame" dates back to 1843 by Mill's hand. The hypotheses non fingo was a wave away to get out of endless controversies with Cartesians and Leibniz, and had little to do with Newton's sentiment or the scientific community's of his time. Both were very much into entertaining hypotheses. In fact, Newton's position was instrumental to the "universally shared" adoption of action at a distance by mid 18th century. It is only after Mill that the tide turned the other way. Apr 21, 2023 at 20:27
• That's what Henry's paper is about. Apr 22, 2023 at 2:42

There have been innumerable physical analyses of locality with respect to both "rigid" and nonrigid bodies; this is a solved problem in both physics and engineering. Metaphysical musings on this topic do not even rise to the level of irrelevance... but that said, don't let me stop you! Muse away, and have fun. It's only metaphysics, after all.