I have a "love/hate" relationship with the phrase “gravity is not a force”.
“Love”, in the sense that it relates to an area of physics I'm particularly interested in and “hate”, in that (as unfortunately with many such things) it’s sometimes used as a “Gotcha!”, to try and put people down, make the person who’s using it feel superior (Hah!... I know more than you!) etc. 1/5
So (as with many statements), the “correctness” of “gravity is not a force” is context dependent.
The statement in-and-of-itself, is of limited importance. If one wants to understand more about gravity, it’s about understanding the ideas related to this statement. Understanding what is meant by the statement.
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@level98 The thing I don't get is, assuming Einstein is the best model we have for gravity, why do physicists still talk about gravitons? If there's no force, there's no field; no field, no excitation resulting in a particle.
I'm very ignorant on a lot of this stuff, and welcome any criticism of any misunderstandings above.
@MichaelPorter Addendum: This is one of he disagreements about ways forward e.g. String Theory (really, "Sting Hypothesis") has "gravitons" i.e. essentially gravity *is* a force. On the other hand, LQG (Loop Quantum Gravity) people argue this must be wrong because any model has to be "background independent" (gravity not a force) as in LQG.
Though one should also note, String Theory is attempting to be a TOE (Theory of Everything). LQG is just trying to be a "quantum theory of gravity".
@level98 I'll take the weasel words as a given 😄
If I ever find the time, I'll have to read up more on this.
@MichaelPorter Good point!
It's the best model we have for gravity... so far.
If one were able to come up with a QFT-like (quantum field theory) version of gravity, then the graviton is the name given to the hypothesised excitation of the gravitational QFT-like field. Many physicists implicitly assume this will eventually happen and so discuss gravitons as if it has already happened.
Physicists are lazy... I mean efficient... continually saying "so far", "hypothesised" etc. can be tedious! 😀