On 7/26/2013 3:43 PM, Warp wrote:
 >
> Anyway, according to general relativity, spacetime *is* four-dimensional,

Slight quibble: The 4d-spacetime stuff was already in special 
relativity.  General relativity added gravity into the mix, but the 
theory of 4d (Lorentzian) spacetime was there already.

What you say is of course technically correct since general relativity 
includes special relativity as a sub-case, but I think it's cleaner to 
separate the two for the purposes of talking about the 4th dimension in 
general.

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