PeterDonis said:I see the similarity: both examples involve something that's postulated to be part of a physical theory but is "unobservable" (the flat background spacetime and the "absolute rest" frame). But the two examples are not quite the same. In the massless spin-2 field example, there's no need to commit to any particular state of motion as being "at rest". You just have to accept that the flat background is unobservable, because all actual physical measurements are governed by the "curved" metric produced by the massless spin-2 field.
With LET, you have to believe that there is some particular state of motion that corresponds to "absolute rest", we just have no way of ever telling which one it is by experiment. Also, the "absolute rest" frame in LET, corresponding to the "absolute rest" state of motion, is *not* a Newtonian absolute space/time. It's a Lorentz inertial frame; there's just no way of knowing *which* Lorentz inertial frame it is. LET is *not* a theory that adds Lorentz length contraction/time dilation "on top of" Newtonian absolute space and time; there is no such theory, because Newtonian absolute space and time is incompatible with Lorentz invariance (it would require Galilean invariance, corresponding to an infinite speed of light).
stglyde said:Uhm.. if this is so. How come when Lorentz discovered the Lorentz Transformation. He didn't immediately explore Minkowski Spacetime. He actually thought the physical length contracting was enough to explain it. It took Einstein to discover the Minkowski mechanism. So it could be assume Lorentz Transformation as Lorentz thought it can be an addition to Newtonian absolute space and time.
PeterDonis said:Actually, Einstein didn't discover Minkowski spacetime; Minkowski did. (Yes, I know things aren't always named after the people who actually discovered them, but in this case it happened that way.) You may be using the term "Minkowski spacetime" more generally than it's normally used; normally it doesn't just refer to SR in general, but to the particular geometric object, a 4-dimensional manifold with a particular metric, that can be used to model SR. As I said, Einstein didn't come up with that; Minkowski did, and Einstein only adopted it when it became clear to him that he needed a geometric model for general relativity, and that Minkowski's flat spacetime was the limiting case of that model when gravity is absent.
I'm not familiar enough with Lorentz's papers to know whether he thought at first that his results could be explained by just adding on length contraction to Newtonian space and time. But I don't think it really matters, because Einstein's 1905 relativity papers did make it clear that that wasn't possible; that to make kinematics consistent with the speed of light being constant for all observers, you *had* to give up Newtonian space and time.
stglyde said:Thanks for the important distinctions. I'm interested in all this because I'm looking for lorentz violations.
stglyde said:How do you think the quantum vacuum connect with spacetime? Is the quantum vacuum inside spacetime or is spacetime inside the quantum vacuum? They say the quantum vacuum doesn't have a rest frame.. so it's like its connected to spacetime as if part of the manifold.
stglyde said:We still haven't refuted Dirac sea of Electrons where the vacuum is composed of negative sea of electrons.
stglyde said:I wonder if the quantum vacuum can also have spontaneous symmetry breaking where if you can alter it at certain configuration from the default ambient background.. it would no longer follow lorentz symmetry.. and hence lorentz violations detected. What are the arguments that makes it impossible that the quantum vacuum can change default mode to another phase or level?
PeterDonis said:Actually, Einstein didn't discover Minkowski spacetime; Minkowski did. (Yes, I know things aren't always named after the people who actually discovered them, but in this case it happened that way.) You may be using the term "Minkowski spacetime" more generally than it's normally used; normally it doesn't just refer to SR in general, but to the particular geometric object, a 4-dimensional manifold with a particular metric, that can be used to model SR. As I said, Einstein didn't come up with that; Minkowski did, and Einstein only adopted it when it became clear to him that he needed a geometric model for general relativity, and that Minkowski's flat spacetime was the limiting case of that model when gravity is absent.
I'm not familiar enough with Lorentz's papers to know whether he thought at first that his results could be explained by just adding on length contraction to Newtonian space and time. But I don't think it really matters, because Einstein's 1905 relativity papers did make it clear that that wasn't possible; that to make kinematics consistent with the speed of light being constant for all observers, you *had* to give up Newtonian space and time.