Talk:Aether drag hypothesis
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[edit] Flat spacetime as the absence of physics?
SR cannot easily be 'wrong', being a theorem in differential geometry. loxley 08:38, 27 July 2005 (UTC)
If you are referring to the idea that any curved-spacetime problem has to reduce to flat spacetime over small regions, I think that the consequences of this tend to be misunderstood by physicists … that geometrical result does not automatically mean that curved spacetime also has to reduce to flat-spacetime physics.
The condition of flat spacetime might instead be the limit a which all meaningful physics disappears – no physical particles to play with, no identifiable field “features” to propagate or interact, a level and uniform field as a zero-particle solution. At this zero-particle limit, you don’t have to modify a smooth metric to allow “mathematical” observers to see “mathematical” particles to be obeying the principle of relativity in the region, because the geometry of the region has already told us that no such particles or observers exist there. Applying Einstein’s early approach of concentrating on the observables in a situation we can say that perhaps it’s not a law of nature that all observers see the principle of relativity being upheld, but rather that nobody sees it being broken. No observer, no breakage. That sort of thing starts to get into QM territory, but perhaps that’s not such a bad thing.
Suppose for a moment that the sort of dragging effects that we see with particulate matter and predict for gravitational fields are a fundamental aspect of moving-body problems: we take a piece of universe, zoom in on it until it becomes effectively flat, place a pair of particles in that flat “arena”, give them a relative velocity … and predicting the shift in a light signal passed between them is no longer a flat spacetime problem, because what we did in the flat spacetime region modified it.. We can zoom in further to get “flat” again, but only by refusing to look at regions that include the particles. In this scenario, flatness does not define the limit at which GR reduces to SR, it defines the limit at which physics effectively ends. We can’t reasonably prove the kinetics of moving-body problems on the basis of a geometry that is only valid when we guarantee the complete absence of moving bodies. We certainly might try that approach in the hope that the resulting relationships will then turn out to be robust enough to stand up to the introduction of more realistic particles, but in the case of SR they aren’t.
It might however not apply to the universe. We could, for instance, suggest as you have done that the distribution of material in the universe is finely adjusted to appear like a hyperbolic geometry. It seems a bit odd however to favour a 3D Euclidean space to such a degree that we are prepared to suggest effects that are specifically adjusted to make it look like hyperbolic space. loxley 08:38, 27 July 2005 (UTC)
No, I'm not suggesting we live in a 3D euclidean metric that just happens to look like the SR metric: I'm suggesting that, if we take dragging effects seriously, and treat them relativistically, we must be living in a velocity-warped non-Euclidean metric that generates equations of motion that must then be recognisably, measurably, physically different from those of SR. I'm saying that the whole SR-based structure of C20th physics may have been founded on an inadequate set of geometrical relationships that don't work properly in curved spacetime, and seem fundamentally incompatible with the general principle of relativity. We have GR, but it's been hacked about to stop it contradicting SR, and consequently doesn't "fit" QM or its original design brief. Experimental verifications of SR typically concentrate on showing that SR is better than a non-relativistic flat aether model, or showing then NM superimposed on a flat background doesn't work (which it doesn't), but there's no obvious test theory to tell experimenters how to test for SR being the wrong theory of relativity.
What I actually favour is a post-SR non-Euclidean metric redesigned from the ground up, in which GR concepts of local c and spacetime curvature apply not just to acceleration and rotation but also to conventional mechanics. Acceleration drags light, rotation drags light, velocity drags light, kinetic energy stored in the metric as spacetime curvature, no information transfer without geometry change. A single geometrical paradigm for everything, fully compliant with the general principle of relativity (unlike the rather Frankenstein-ey thing we have now). But it seems that in order to do that, we have to ditch special relativity and make the theory “curved” all the way down. To me it’s possibly the last major challenge in classical physics, with Einstein throwing down the gauntlet in 1950, but most theoreticians seem to get an attack of vertigo at the idea of losing their SR safety net and prefer not to look over the edge. I find this attitude unimpressive.
Anyway, back on topic: if you want a unified relativistic theory that can't be reached via SR, and your working assumption is that such a theory really exists, and has a wider range of applicability than SR, then a good way to proceed would seem to be to take all the things that SR can’t cope with, and presume that since they can’t be optional (or SR could do them), and can’t be forbidden, they must be mandatory. So you dig up all the effects that violate SR and turn them from bugs into features: you say: the hypothetical final theory hasn’t been found by the SR guys because it only works if you embrace dragging effects, and gravitational mass, and particulate behaviour, as essential parts of what makes mechanics work. And then you find that these bits do actually work very well together, moving particles do drag light, moving gravitational features really should drag light, light-dragging warps lightbeams and should count as a sort of spacetime curvature, and that’s why SR –based approaches can’t enter this territory and stay consistent. Light-dragging as a mechanism for local lightspeed constancy requires more complex geometry than SR, but it you can crack that, you’ve also probably got gravity and cosmology and gawd knows what else all working off the same mechanism. Next-generation single-layer physics.
If this hypothetical theory does exist, and has these characteristics, I don’t see how we’ll be able to find it by starting with the assumption that SR is correct. It seems instead that to get a full general theory of relativity you probably have to assume that the final theory can’t reduce to special relativity’s physics, and then that it can’t reduce to SR’s math, either.
So to me, these "non-SR" dragging effects are potentially quite important. Rather than being archaic C19th leftovers, they might be the key to post-SR C21st relativity theory. ErkDemon 03:09, 3 August 2005 (UTC)
