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Posted by Bruce on May 30, 2004 22:33:30 UTC

""The general theory reduces to the special theory for the special case where gravity isn't present"". "Can you point out where in the universe that gravity is not present?"

I don't need to point out where gravity isn't present because I can always 'find' a sufficiently small spacetime region where spacetime is approximately flat. All local physics can be done using the mathematics of SR. It is a result of the equivalence principle.

"At every spacetime point in an arbitrary gravitational field it is possible to choose a locally inertial coordinate system such that within a sufficiently small spacetime region, the laws of nature reduce to those found in special relativity for an unaccelerated Cartesian coordinate system."

The blunder Einstein thought he made was introducing the cosmological constant to the metric. Turns out he didn't need it when Hubble showed the universe is expanding. It also turns out that something resembling the cosmological constant will be needed to explain the acceleration phase our universe is in presently.

A good non-mathematical book to read on grav physics is Kip Thorne's Black Holes & Time Warps. A good introcuction to SR is Taylor and Wheeler's Spacetime Physics. A good introductory to GR is Taylor and Wheeler's Exploring Black Holes. The last two require mathematics up to and including calculus. The last book is really a gem because it introduces undergraduates to GR needing only 'up to calculus' and the solutions [metric equations] to Einstein's equations.

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