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One of Feyman's famous quotes is

"If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another."

It seems that he could only be referring to the electromagnetic force since the other three fundamental forces don't apply. But I'm having trouble visualizing this. My question is, how, based upon different distances, does the electromagnetic force produce the two opposite forces Feynman mentions?

D. Ennis
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    I am afraid that "It seems that he could only be referring to the electrostatic forces between protons and electrons, since the other three fundamental forces don't apply." is a false premise. That's about inter-atomic forces. (For instance the Lennard-Jones potential or something similar). – dmckee --- ex-moderator kitten Jan 31 '18 at 17:39
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    See Is the electromagnetic force responsible for contact forces? for the repulsion bit and Google London dispersion force for the attractive bit. – John Rennie Jan 31 '18 at 17:47
  • @dmckee, so which of the four fundamental forces (strong nuclear, weak nuclear, electromagnetic, or gravitational) are you saying is involved in "inter-atomic" forces? – D. Ennis Jan 31 '18 at 17:48
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    @D.Ennis I think David's point is that the long range attraction is a dipole-dipole force not an attraction between electrons and protons. But both are of course examples of electromagnetic interactions. – John Rennie Jan 31 '18 at 17:51
  • @JohnRennie I'll check out the references you provided. Thanks. – D. Ennis Jan 31 '18 at 17:55
  • I have edited my question based upon the above comments. – D. Ennis Jan 31 '18 at 17:58
  • @D.Ennis that's a useful clarification, though to be honest I think dmckee was being a bit fussy about the wording. I knew what you meant :-) – John Rennie Jan 31 '18 at 17:59
  • The Ancient Greeks already gave us the concept of the "atom", which meant "uncuttable", and was embraced in 19th century chemistry. But then the atom was cut into subatomic particles (to which Feynman made great contributions), so I'd be surprised if Feynman's own pearls of wisdom were still considered current in another 100 years! – Steve Jan 31 '18 at 19:02
  • I would add that the sentence does not rules out atoms from reacting to "made all things" Moreover gravity can bring atoms to those little distance, at first. – Alchimista Jan 31 '18 at 19:07
  • Hmm ... I read the original version as being about the interactions within an atom, and felt that was wrong enough to need addressing. Of course the inter-atomic forces are largely electromagnetic in nature, but they act between systems (atoms) that have a complex internal structure giving rise to the non-trivial shape of the effective potential. But Feynmann's sentence doesn't tell the reader anything about the substructure of atoms. Presumably he thought that you can get chemistry and statistical physics and thereby bootstrap civilization without knowing about atomic internals. – dmckee --- ex-moderator kitten Jan 31 '18 at 20:09
  • Why do you think this statement is about a fundamental force? It seems clear to me that Feynman simply thought that telling people with no scientific knowledge whatsoever, not even the concept of force, that the things they see and touch are eventually made of dynamic tiny elementary atoms was the best way to put them on track. The part about repelling comes from plain logic: if Feynman just had said "atoms attract each other" then the imaginary people, ignorant but not stupid, would have dismissed the claim as illogical since they could see that all matter is not aggregated into a big clump. – Stéphane Rollandin Jan 31 '18 at 21:03
  • Or, to put it another way, if you have only one sentence to utter, it is much more effective to make it inspiring than to make it technically rigourous. – Stéphane Rollandin Jan 31 '18 at 21:11
  • Feynman was writing the foreword to the published volume set of his Cal-Tech lecture series when he said this. He had lots of time to think about what he was saying. – D. Ennis Feb 02 '18 at 13:15

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