maxwell wrote:
On Dec 24, 7:57 pm, Tom Roberts wrote:
SR is the local limit of GR in any manifold, but that is only
approximate.

Tom, I would appreciate a reference to a published demonstration that
SR is the approximate limit of GR.

Look in the beginning chapters of any textbook on GR. This is basic to
the formulation of GR.

For instance: Geroch, _General_Relativity_from_A_to_B_.
This is a non-mathematical introduction to the concepts of
GR, but I think it discusses this. Otherwise pull out the
big guns:
Misner, Thorne, and Wheeler, _Gravitation_.
Wald, _General_Relativity_.
... or other textbooks by Schutz, etc.


I thought Einstein wasted the last
40 years of his life trying to unify these two theories. Isn't this
why quantum-gravity is still a hot research topic: SR is about
electromegnetism (and so, eventually covered by QM) while GR is about
gravity?

You are confused. SR is inherent in GR by simply applying GR to the
Minkowski manifold. What Einstein tried (unsuccessfully) to do is to
unify GR and electrodynamics. The search for quantum gravity is a whole
different kettle of fish -- Einstein was working with Maxwell's
equations, which we now know are only an approximation to QED, and this
is likely a major aspect of his failure. The real problem is unifying GR
and quantum mechanics....

BTW SR is more general than just electromagnetism -- it applies to the
entire standard model of particle physics (i.e. also to weak and strong
interactions, as well as to electrodynamics). This is a quantum theory
consistent with SR, but it is not consistent with GR.


Tom Roberts