Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site rlgvax.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!zehntel!tektronix!hplabs!hao!seismo!rlgvax!guy From: guy@rlgvax.UUCP (Guy Harris) Newsgroups: net.physics Subject: Re: quo vadis gravity? Message-ID: <300@rlgvax.UUCP> Date: Wed, 12-Dec-84 21:44:36 EST Article-I.D.: rlgvax.300 Posted: Wed Dec 12 21:44:36 1984 Date-Received: Sun, 16-Dec-84 06:47:46 EST References: <184@decwrl.UUCP> <181@talcott.UUCP> Organization: CCI Office Systems Group, Reston, VA Lines: 25 > > > > >The gravitational field does not "travel" at all. > > > > If e=mc**2 and matter and mass are converted in an atomic bomb... shouldn't > > something happen to the gravitational field of the "former" mass? > > A common myth: mass is not conserved, energy is not conserved, but the sum > of the two is. This myth is in part propagated by Isaac Asimov and other > popular science writers. Now here's reality: Mass *is* energy, and it is > conserved. In fact, one more conservation law was thrown in: momentum. > Whereas B.E. (before Einstein), we had the conservation of mass, the > conservation of energy, and the conservation of momentum, A.E. (after > Einstein), we have the conservation of energy-momentum (energy being equal > to mass). Energy can be thought of as "momentum in the time direction". And, since the source of the gravitational field is energy-momentum (well, actually it's the stress-energy tensor, which more-or-less is to energy-momentum as electric charge/current density is to charge, so energy-momentum is actually the "charge" that generates a gravitational field), the "former mass" is still around, because the energy-momentum of the bomb before the explosion and after is the same (by conservation of E-M); therefore, the gravitational field may be changed but it doesn't "go away". Guy Harris {seismo,ihnp4,allegra}!rlgvax!guy