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byron178
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Why does faster than light travel or propagation mean time travel backwards to violate causality?
DrGreg said:
byron178 said:Why does faster than light travel or propagation mean time travel backwards to violate causality?
DrStupid said:Because of the relativity of simultaneity. If you are traveling faster than light then there are frames of reference where you arrive before you start and that's a violation of causality.
HallsofIvy said:That is one possible interpretation of the Lorenz time contraction formula where, if it were possible for v to be larger than c, then t becomes an imaginary number. A more reasonable interpretation would be that this is yet another reason why one can't go faster than c.
byron178 said:how come entanglement happens faster than light?
byron178 said:is there anything is physics that travels simultaneity?
DrStupid said:Because nothing travels and no information is transmitted.
jtbell said:What do you mean by "travels simultaneity?"
DrStupid said:Because nothing travels and no information is transmitted.
byron178 said:also i forgot to add,can something travel backwards in time and not violate causality?
easyrider said:Would it be possible to use quantum entanglement to communicate at any usable distance?
Mordred said:In a similar manner to how two computers talk to each other then yes, Provided they can get the entanglement stable enough to be practical. It could be a usable wireless communication without the use of light or radio. There was a recent article concerning a diode that they fashioned that can generate several million entangled particles per second. I can't recall the exact amount, However certain types of radiation tends to break the entanglement down rapidly, Again its been a few months since I read that article so cannot name the particulars on it. To the best of my knowledge the maximum distance I've heard they achieved is 100 km.
xeryx35 said:People might want to use up-down spins to correspond to 1s and 0s on one end, and because the opposites will occur on the other, for 1s and 0s to be reversed so as to decode the original message. However, I'm pretty sure that once you try to measure the state of the atom, proton, whatever, it gets manipulated, so whatever you happen to send through quantum entanglement will be corrupted and nothing usable can be actually read.
DaveC426913 said:No, the problem is, that what you read about the state of the entanglement at the receiving end does not tell you anything - unless and until you communicate with the source - which you can only do at luminal or subluminal speeds.
kmarinas86 said:If the spacetime continuum is an unviolated principle of nature, then faster than light travel requires backwards time travel.
kmarinas86 said:given that the scientists at CERN have measured a positive velocity in their experiments, then discovery of FTL travel would be directly incompatible with the existence of a space-time continuum, as presently defined.
DrStupid said:It requires backwards time travel in some frames of reference but not in all frames of reference.
That the scientists at CERN have measured a positive velocity in their own rest frame wouldn't mean that the velocity is positive in every frame of reference.
kmarinas86 said:What do you call a velocity [...]?
kmarinas86 said:And the focus here anyway is the velocity of neutrinos measured from the laboratory frame in which point A and point B are fixed coordinates.
DrStupid said:The derivation of the position with respect to the time.
DrStupid said:If you want to have "backwards time travel" you will have to change the frame of reference.
DrGreg said:All you can do with entangled particles is read what state they are in. As soon as you try to write a new state, the particles are no longer entangled.
kmarinas86 said:I'm not talking about comparing frames of reference. We are discussing velocity respect to the laboratory frame
xeryx35 said:So does this mean that the programmer who wrote the program to "make sense of "the entanglement results, and the fact that the skills to use a computer to "make sense of" the data were taught to the crew, was the necessary subluminal communication component? How does it work, I don't really have a physics background so I don't understand it too well.