Something’s been bugging me about reports on recent Faster Than Light (FTL) travel experiments.
As i understand matters, it has been demonstrated that if you entangle two particles, separate them in space and then cause one’s state to decay, the other particle suffers similar decay perfectly instantaneously.
This is FTL travel, but all that is being sent is information. My understanding of relativity (general at least) is that it describes and constrains the behaviour of matter with energy or mass or both. Information has neither, so relativity is OK after all, huh?
Please now feel free to open up the vast vistas of ignorance i did not know i even possessed.
Hopefully, Chronos will clear all this up, but I’ll just say that Relativity does address “information” in the sense that a signal cannot be transmitted FTL. The types of effects on particles that you are talking about falls under Quantum Mechanics (where GR/SR cannot be directly applied).
No information can travel faster than the speed of light!
I think you are refering to Bell’s theorm AKA Bell’s inequality. There is no transfer of information. You don’t change the state of one particle and find a corresponding change in the other particle. Instead if you measure the spins of a set of entangled particles, there is a correlation in the spins of the partner particles. If you assume that particles have a definite spin whether you measure them or not, then the correlation must travel faster than light. However this correlation is only revealed when the results are compared. The standard interpretation is that the spin is not defined until it is measured. But no matter how you interpret the results, no information travels faster than light.
I’d just like to address three issues here: First off, Special Relativity does, in fact, address information. It doesn’t explicitly say that FTL transmission of information is impossible, but it does say that FTL transmission of information is equivalent to transmitting information back in time, which can be problematic. Secondly, “simultaneous” is not defined in modern physics, unless you either define a specific reference frame, or put the events at the same place, as well. Thirdly, quantum mechanics, like every other branch of physics, has been brought in line with Special Relativity (which is all we need here, anyway), and is perfectly consistent with it. Theproblem only comes when you try to integrate General Relativity and quantum.
As DrMatrix said, there’s a few possible explanations of the Bell effect, but none of them involve FTL transmission of information to an observer. Basically, although the two observers will see correlated states, neither will be able to control which state he or she observes, and so cannot transmit a state of his choice.