Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/3/84; site talcott.UUCP Path: utzoo!linus!decvax!genrad!wjh12!talcott!gjk From: gjk@talcott.UUCP (Greg J Kuperberg) Newsgroups: net.physics Subject: Re: Re: why FTL is illegal, in small words Message-ID: <119@talcott.UUCP> Date: Tue, 20-Nov-84 12:29:25 EST Article-I.D.: talcott.119 Posted: Tue Nov 20 12:29:25 1984 Date-Received: Wed, 21-Nov-84 05:16:11 EST References: <683@gloria.UUCP> <785@ariel.UUCP> Organization: Harvard Lines: 83 >> Here's another version, for people who do not want to fool around >> with relativity: >> You are made up of charged particles, whose courses are determined >> by their charges and masses. When you move, the particles generate >> magnetic forces - this is the Oersted effect. The fields slow down >> the particles, and interfere with the effect of any outside force. >> At the speed of light, the magnetic forces exactly counteract the >> electric forces, time stops, and outside forces have no effect. >> Not that any of this is what Oersted has in mind ...-- Col. G. L. Sicherman >1.) Time stops? What is time and under what conditions does time stop? >What does it mean to say that time stops? >2.) "whose courses are determined by their charges and masses." Did you forget >free will? >You mean someone trying to understand the illegality of FTL travel should trade >an explanation based on relativity for one that requires answers about time and >free will? >I sure would like to learn from someone who understands all about relativity, >time and free will. I'm not really being all that facetious... >Norm Andrews, vax135!ariel!norm First, the answers to your questions: Time means evidence of change in the system. If a physical system is doing absolutely *nothing*, that is, the air in it isn't moving, no light is being radiated through it, radioactive decay is not taking place, etc., we say that time has stopped. Basically, the Colonel is arguing that electromagnetic weaken in a system moving at high velocity, and therefore all events in the system slow down. This includes clocks, heart rates, and everything else (actually, the electromagnetic force does not include radioactive decay, but a phenomenon similar to Oersted's effect takes place in the other forces of nature as well). However, the occupant of a space ship moving at high velocity would not notice, since his metabolism would be slowed down just as much as everything else. At the limit of the speed of light, everything stops. A person in a spaceship travelling at the speed of light appears frozen in mid air, the ship clocks having stopped, the ship computer having stopped, and the air itself not moving at all either. Yes, the electromagnetic force is responsible (usually in quantum mechanical form) for almost *every* effect we see, from the why "water is wet" to why we have gases, liquids, and solids, to semiconductor technology. Whether or not free will is a consequence of the electromagnetic force is a question of theology, but the Colonel was going under the assumption that it is. Mind you that special relativity is a simple, but tricky, derivation from Maxwell's equations. The Colonel's argument works for plain-Joe travel, but one could still ask, "couldn't there be something like hyper-space leaps, where you don't really move faster than light, but you can arrive at your destination quickly nevertheless?" Here is a stronger argument against FTL travel: One of the first consequences of special relativity is that simultaneity is not conserved. If you have two events that happens at the same time at different places, then a moving observer would not only *see* them happening at different times, but even taking into account the finite speed of light, he would *deduce* that they must have happened at different times. In fact, under certain circumstances, the order of occurence of two events can be switched. Suppose you have two people, at positions A and B. Suppose that at time t0, the person at A turns on a flashlight pointed at B. Suppose that at time t1, the person at B sneezes, and at time t2>t1, the light arrives at B. Then for some moving observer, B sneezed *before* A turned on the flashlight. 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. This causes a whole slew of problems. If I can travel backwards in time, I could, for example, go back and kill my grandfather before my father was conceived. I would have to then cease to exist (as would my father). But if I never existed, who killed my grandfather? It's because of nonsense stories like this that people say that FTL travel is impossible.