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Article #848Re: An easy problem in general relativity
From: John C. Baez
Date: Fri, 07 Aug 1992 16:16
Date: Fri, 07 Aug 1992 16:16
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In article <1992Aug7.092922.11852@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes: >Question: what is the mass of the object represented by the >Schwarzschild solution? >Answer: Zero. Exactly zero. It's a vacuum solution, remember? >Comments? [Please don't tell me that the mass is all squashed up "inside >the singularity".] True, it's a vacuum solution, but the notion of "mass" in general relativity is most precisely captured by the formula for the mass of an asymptotically flat solution of Einstein's equations. This formula expresses the total mass in terms of quantities that can be measured at spacelike infinity (i.e. far far away). Basically, far enough away the Newtonian approximation is okay and you can orbit a test particle around and figure out what it seems the "mass" of the system is. By this definition the Schwarzschild solution has nonzero mass.
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Newsgroups: sci.physics Path: arc1-ca.pugleaf.net!sparky!uunet!snorkelwacker.mit.edu!galois!banach!jbaez From: jbaez@banach.mit.edu (John C. Baez) Subject: Re: An easy problem in general relativity Message-ID: <1992Aug7.161604.21263@galois.mit.edu> Sender: news@galois.mit.edu Nntp-Posting-Host: banach Organization: MIT Department of Mathematics, Cambridge, MA References: <1992Aug7.092922.11852@nuscc.nus.sg> Date: Fri, 7 Aug 92 16:16:04 GMT Lines: 15