# Why does the universe require relativity? [closed]

Are there any known compelling reasons why our universe is governed by relativity instead of Newtonian physics?

I recognize that an infinite $$c$$ would be a problem, so I'm not asking about that; I figure that so long as you still conserve energy and momentum etc., everything would be limited to arbitrarily large but finite speeds, ensuring that causality remains intact and preserving our computationally tractable universe.

I suspect that there are lots of instances where relativity informs our understanding of the operation of stars or subatomic processes or what have you, but which if any of those kinds of things couldn't be more easily explained with a Newtonian outlook?

In case it helps, my motivation here is to try and understand whether relativity makes sense from an Occam's razor perspective. And I know that relativity fits all our observations beautifully, and that it's all implied once you accept that physics are invariant in any reference frame, but that all doesn't strike me as the simplest a priori arrangement we could have had for a universe, and I find that possibility unsettling.

• The problem with questions like this is that what you regard as simple or obvious is a matter of opinion. The valid in all reference frames criterion that you cite is called general covariance and most physicists would regard it as a remarkably simple principle and it makes a lot of sense that it applies to the universe. Now it turns out that Newtonian mechanics can also be formulated in a generally covariant way, but when you do this the result is messy and compicated while formulating GR is simple and clear. – John Rennie Jun 7 '19 at 8:22
• Indeed, GR is arguably the simplest possible generally covariant theory that could describe the universe. So the fact that the universe requires GR (to use your phrase) is because GR is the simplest possible theory the universe could require. – John Rennie Jun 7 '19 at 8:23
• Probably not exactly relevant, but there is a derivation in Rindler's book Relativity: Special, General, and Cosmological that shows, given a few symmetry assumptions, that Galilean transformations and Lorentz transformations are the only possible "relativity transformations." You still need some empirical fact to decide between the two types of transformations, but it is interesting nonetheless. Something like this seems to do the same thing. Imo, I don't find these derivations enlightening though, because they seem hard to follow. – Maximal Ideal Jun 7 '19 at 9:02
• simplest a priori arrangement we could have had for a universe is no universe at all with no physics to worry about. From occams razors perspective mainstream relativity is the simplest theory we could think about that is consistent with the observed facts. Just read something about eather theory that predated relativity and tried to explain constancy of light using newtonian frame of thoughts.They basicly "explained" everthing relativity can, but the theory was very artificial and ugly and opened up new questions about why is the eather so strange. – Umaxo Jun 7 '19 at 10:21
• I'm voting to close this question as off-topic because it's largely a question about philosophy instead of physics. – Kyle Kanos Jun 7 '19 at 11:29