Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site duts.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!ihnp4!nsc!amdahl!duts!shiva From: shiva@duts.UUCP Newsgroups: net.sf-lovers Subject: Re: Time travel, center of mass Message-ID: <153@duts.UUCP> Date: Fri, 1-Nov-85 16:52:35 EST Article-I.D.: duts.153 Posted: Fri Nov 1 16:52:35 1985 Date-Received: Mon, 4-Nov-85 02:21:23 EST References: <291@caip.RUTGERS.EDU> Organization: Amdahl Corp, Sunnyvale CA Lines: 31 > From: Alan Wexelblat> .... Is it the case that the center of > mass of the universe doesn't move? Is is (theoretically) possible to > calculate our position/velocity w.r.t. this non-moving point? On the contrary, the center of mass of the universe must move, since all the masses in it are constantly moving. Mass is constantly being redistributed hence the center of mass has to move *with respect to any other mass*. It does not make sense to talk about the center of mass moving with respect to anything else, because there is no absolute frame of reference (thanks to Dr. Einstein). As to calculating our velocity with respect to the center of mass at any one instant, well, wouldn't you have to know the position of every other mass in the universe at that instant? You can't do this because of the speed of light (even assuming you could accumulate all that information in some computer) which will only tell you where any particular mass was sometime in the past. Now, having said all this, this is sf-lovers after all, so anything is possible...... Disclaimer: I am not a Theoretical Physicist, although I play one on TV..... "Anything is possible. Unfortunately, most of it is so damn improbable." -- me -- Shiva, Amdahl