Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site uwmacc.UUCP Path: utzoo!linus!philabs!cmcl2!harvard!seismo!uwvax!uwmacc!demillo From: demillo@uwmacc.UUCP (Rob DeMillo) Newsgroups: net.sf-lovers Subject: Re: Time travel, take 2 Message-ID: <1656@uwmacc.UUCP> Date: Tue, 5-Nov-85 13:10:50 EST Article-I.D.: uwmacc.1656 Posted: Tue Nov 5 13:10:50 1985 Date-Received: Fri, 8-Nov-85 05:49:51 EST References: <291@caip.RUTGERS.EDU> Organization: UWisconsin-Madison Academic Comp Center Lines: 41 > From: Alan Wexelblat> > Thanks to those who replied to my earlier posting on time-travel. > One thing still puzzles me though: 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? People > seem to talk about our universe as expanding, but exapanding away from > what? > --Alan Wexelblat > WEX@MCC.ARPA If we are to believe Einsteinian physics...there is no center of the Universe. When astrophysicists speak of the Universe expanding, they are not talking about galaxies fleeing away from a common center. What is being talked about is the fabric of spacetime (one word, please) being expanded, and everything on it is going along for the ride. The common analogy that is used is: consider the Universe as the dough for raisin bread. The spacetime is the dough, and the raisins are everything else. (i.e. galaxies, stars, people, small marine mammals, whatever) As you let the dough rise, or expand, it appears (regardless of what raisin you happen to be) that all the other raisins are rushing away from you. The result: everyone is rushing away from everyone else, but there is no common center. A subtle, but important, difference.. -- --- Rob DeMillo Madison Academic Computer Center ...seismo!uwvax!uwmacc!demillo "...I suppose you think the concept of a robot with an artificial leg is amusing?" -- Marvin, the Paranoid Android