biep@cs.vu.nl (J. A. "Biep" Durieux) (06/03/87)
>> So it turns out that signals (information transfer) faster than light are >> NOT possible by exploiting this "effect" (whatever it is). ... >> (If it had turned out differently, I would have been very annoyed, since >> it would utterly destroy the credibility of quantum theory in my view.) > >What is so bad about FTL communication? Granted, it would mean there >is either an absolute frame of reference somewhere or causality can be >violated. Most likely the latter. > ...Keith Not even necessary. Causality only would show not to be bound by light speed, as was thought until now. Before Einstein many people thought that, and didn't seem to have any problems with it. Another question: is there any inherent reason why our velocities are so *much* lower than light's? There is a story 'if light went with 55 mph', which made me wonder. i n e w s f o o d . -- Biep. (biep@cs.vu.nl via mcvax) Some mazes (especially small ones) have no solutions. -- man 6 maze
ogil@sphinx.UUCP (06/04/87)
[I've directed followups to sci.philosophy.tech, in an attempt to keep this discussion in one group]. In article <785@klipper.cs.vu.nl> biep@cs.vu.nl (J. A. "Biep" Durieux) writes: >>What is so bad about FTL communication? Granted, it would mean there >>is either an absolute frame of reference somewhere or causality can be >>violated. Most likely the latter. >> ...Keith > >Not even necessary. Causality only would show not to be bound by >light speed, as was thought until now. Before Einstein many people >thought that, and didn't seem to have any problems with it. >-- > Biep. (biep@cs.vu.nl via mcvax) Causality would not be violated for observers in the same inertial frame of reference, but it would be for observers moving relative to one another. Consider the following example: ILLUSTRATION 1: Space-time Diagram ----------------------------------------------------------------------------- t t t t t t s . t s . t ***********B . y A********** ###### s . y t ###### s . y C###### s . y t s . y t s . y t s. y t s y t .+ t .ys *xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx t ----------------------------------------------------------------------------- Let two observers be moving at a high velocity relative to each other (say .99 c). Observer 1's world line is represented by the t's, and his spatial axis by the x's. Observer 2's world line is the line of s's, and his spatial axis is the line of y's. The .'s represent the world line of a photon. Now, assume that each observer has an FTL gun (it shoots bullets at FTL; don't worry about the energy problems). 1 shoots his gun at 2 (the event marked A), and the bullet's world line is represented by the *'s. The bullet intercepts 2's world-line at event B, but 1's aim was off and he misses 2. 2, being upset by this hostile action, fires his gun at 1. The bullet's world line is represented by the #'s, and it is moving in the positive direction with regard to 2's time axis (world line). It intercepts 1's world line at C, killing him. Unfortunately, 2 has killed 1 before 1 fires the offending bullet. This presents something of a problem :-). By examining the space-time diagrams on paper, where precise drawings are easy to make (compared to a terminal, at any rate), one can see that causality is violated when information is transferred at a velocity greater than the reciprocal of the observers' relative velocity. Since the observers can move as close to c as we want, c is imposed as the limit of information transfer between the two. In order to preserve causality, one has to throw out special relativity, which has been confirmed too many times to be false. Thus, FTL information transfer is impossible (unless you want to go all the way and eliminate causality! :-). -- __________________________________ "Display me Aeolus above Brian W. Ogilvie | Reviewing the insurgent gales ...{uwvax,hao}!oddjob!sphinx!ogil| Which tangle Ariadne's hair ogil%sphinx@uchicago.BITNET | And swell with haste the perjured sails."