Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site mordor.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!ut-sally!mordor!@S1-A.ARPA,@MIT-MC:gwyn@Brl.ARPA From: @S1-A.ARPA,@MIT-MC:gwyn@Brl.ARPA Newsgroups: net.space Subject: Re: questions about the theory of relativity Message-ID: <1788@mordor.UUCP> Date: Tue, 14-May-85 08:41:40 EDT Article-I.D.: mordor.1788 Posted: Tue May 14 08:41:40 1985 Date-Received: Thu, 16-May-85 06:33:12 EDT Sender: daemon@mordor.UUCP Lines: 52 From: Doug Gwyn (VLD/VMB) > Is it theoretically possible to create a device which, after being > "locked" onto an object (e.g., the Earth), could always tell you your > velocity relative to that object (even after a period of near-light speed > travel, various maneuvers, etc.)? Not really, because it would have to know all about the structure of the region of space(-time) it was operated in. If you happen to know what the structure is (e.g., essentially flat in intergalactic space), then a close approximation could be done by keeping track of perceived accelerations. If the "other object" were another spaceship, it would be even harder, since the device would also have to know how the other object was moving. > I'm not talking about a computer which > would perform calculations based upon a history file of past accelerations, > but rather a "device" which reacts to the accelerations it experiences. What's the difference? > What about a "clock" which would always tell you the time & date on the > other object? Similar situation. Both cases assume that there is a meaning to where the distant object "really is" and what its time "really is"; in general there is no single answer to these questions. > In science fiction stories, the ease with which ships travel through time > without traveling through space has always bothered me. Gee, I find it easy to move through time without moving through space. Rip van Winkle found it even easier.. > Finally (for now anyway), I have heard it said that Einstein's theory of > relativity could be replaced by a quantum theory of gravity. Funny how the people who say this haven't been able to do so. > I'm unconvinced; > it seems to me that they concern fundamentally different aspects of the > universe. Yes, indeed. More relevantly, their conceptual foundations are quite dissimilar. General relativity (more precisely, generalized field theory) is best expressed as a theory about an objective reality. Quantum theory (QED, QCD) fundamentally denies this. Both theories are claimed to work; no single theory has yet been able to unify these two. Most recent such attempts start from the quantum approach; Einstein started from the field theory approach. There are some striking similarities in some of the resulting technical details (e.g., non-Abelian gauge groups for "internal" symmetries) but there are still considerable differences in the concepts.