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On the contrary, they match huge amounts of observed data. If Einstein's equations didn't match any more observed data than, say, Newton's equations, no-one would have bothered adopting them. But there were lots of observed data at the end of the 1800s that didn't quite fit the models we had. Quite a lot were to do with light, but others were slightly weirder, like the precession of Mercury. Then Einstein's equations came along and fixed all of them. They even made predictions about observations yet to be made, like the behaviour of clocks on satellites and spaceships, which are moving fast enough for special relativistic effects to be detectable, but also moving in a different-enough gravitational field for general relativistic effects to be detectable. (Note, GPS relies on knowing and mitigating these effects in order to work accurately. But also, the designers of the first GPS system still weren't 100% sure it was the case, so they made it possible to change whether none, either, or both mitigations were active. It did turn out that both were needed - another win for Einstein.) I suspect that if the "Einstein's equations not quite correct at intergalactic scale" case ended up being right, we would end up with something that's as different from Einstein as Einstein is from Newton. That is, a new set of equations that is functionally incredibly similar to the old ones, but with an extra term which is very nearly constant under most circumstances, but measurably diverges according to some yet-to-be-discovered criteria. With Einstein's equations, this is the Lorentz factor γ, where 1/γ = √(1 - v²/c²). When v is only a small fraction of c, this term approaches 1, and Einstein's equations approach Newton's. Note that in the case of v being small (compared to c), Newton's equations are still useful, and it's perfectly reasonable to use them to calculate motion and energy without including relativistic effects. And similarly, if we were to "replace" relativity with something else, there would be a lot of circumstances where the additional complexity of the replacement wasn't needed, and relativity would still be useful in the scale between Newton and it. |