From: utzoo!decvax!harpo!seismo!hao!hplabs!sri-unix!jackson.PA@PARC-MAXC.ARPA Newsgroups: net.physics Title: Re: Faster than a Speeding Photon Article-I.D.: sri-arpa.365 Posted: Fri Feb 4 17:33:07 1983 Received: Mon Feb 7 01:51:23 1983 Re;"Quantum mechanics seems to be more tangled with causality. In the Bell paradox causation appears to travel instantaneousy (faster than light). It's not clear, however, that this could be used to send signals. The event that is caused at the far end seems to be unobservable (a change in the state function, which is destroyed by observation)." Grumble...as I understand it the Bell Paradox involves a pair of particles that are constrained to occupy distinct states. When the particles are seperated and the state of one measured, the experimenter knows the state of the other particle, instantly without bothersome measurement. While this *seems* to imply FTL transmission of causality there is no way to signal in this fashion. For signalling to occur, the experimenter must be able to modulate the electron source (to send the recipient a spin up or spin down electron) which will happen at lightspeed or less. Then the electron has to travel from the electron source to the receiver, at lightspeed or less. Total time, assuming an instantainious modulator, is equal or greater than the signaling time for light. Of course, if the experimenter does not bother to modulate the source, and measures incoming electrons, then she knows instantly the state of the electrons at the receiver. No information is exchanged between the receiver and the experimenter though. In a sense, they each posess the same information, which traveled at lightspeed from the source. Stephen Jackson Xerox PARC (415) 494-4226