Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site bnl.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!mcnc!philabs!sbcs!bnl!stern From: stern@bnl.UUCP (Eric Stern) Newsgroups: net.physics Subject: Re: Re: why FTL is illegal, in small words Message-ID: <820@bnl.UUCP> Date: Mon, 10-Dec-84 00:05:39 EST Article-I.D.: bnl.820 Posted: Mon Dec 10 00:05:39 1984 Date-Received: Sat, 15-Dec-84 02:41:59 EST References: <683@gloria.UUCP> <785@ariel.UUCP> <119@talcott.UUCP> <374@mhuxt.UUCP> Organization: SUNY StonyBrook Lines: 41 > > On why FTL implies time travel: > > Now supposing I take off for Alpha Centauri and arrive there in less than > > the amount of time that it takes light to get from here to Alpha Centauri. > > Then for some moving observer, I arrived before I left! Thus I have the > > power to travel backwards in time. > > I still don't understand! Some moving observer, who obviously doesn't > understand relativity thinks that you arrived there before you left, and > you believe him? One of the postulates of physics is that any observer in an inertial frame must observe a universe that obeys the same laws of physics as an observer in any other inertial frame. Otherwise there is no point to physics since the universe depends on how you observe it, and not on any intrisic existence of its own. If one observer in an inertial frame sees me getting to Alpha Centauri before I leave Earth, that is the same thing as observing effects before their causes (causality violation) which means that his physics is different from my physics. As I have pointed out above, this is a big no-no. Now, if the theory leads to contradictions, it must be modified. In this case the only allowed modification is to disallow travel faster than light, since the theory makes sense for any speed slower than lightspeed. This is the only allowable theory, because all other pieces follow directly from the observation that the speed of light is constant in all reference frames. Of course it must be noted that there is no experimental evidence for faster than light travel, so the theory holds up. To answer another question about quantized spacetime, the experimental evidence suggests that there is no quantization of these quantities. Since quantum electrodynamics has been experimentally verified to be correct at extremly large energies (10 Gev) and q.e.d. is a continuous theory this must put a limit of space quantization of the order of an electron wavelength at 10Gev or about 1.0e-17 m. Eric G. Stern Dept. of Physics, SUNY StonyBrook NY 11727 stern@bnl.arpa philabs!sbcs!bnl!stern