Could I ask someone with the necessary patience to explain why quantum entanglement as described here doesn't allow faster-than-light communication? I've been told that I'm misunderstanding something by guessing that it might, and if it can be expressed in layman's terms, I'd love to know why.
try inventing a system using the marbles i describe in an answer above. you just go round in circles. the problem is that there's no "useful" information "coming out".
two people are both observing random processes. they happen to see related results, but they don't "know" that unless they get together and compare notes.
it's like you and i both flip a magic nonlocal coin, and we both flip heads. how does that let me tell you something? it doesn't. all you know is that i just flipped heads (and really you don't even know that - you only know that if i had flipped the coin, i would have seen heads...).
Quantum entanglement allows you to know something about a far-away system that you couldn't have been told by communication, but you can't control what information is passed. Essentially, you both get a random result, it's just that you both happen to know what result you both got. That doesn't allow you to communicate anything to each other. The best it does is allows you to both get the same random number at the same time.
Try constructing an experiment where one side answers a predetermined question, and you'll notice that you can't.
Why can't I combine quantum entanglement with the two slit experiment? Observing one particle will collapse the other's quantum state, so lead to a classical result for the dual split experiment rather than a quantum one?
That's true that it allows faster-than-light communication is some sense, however it is not clear if it is possible to use quantum entanglement for faster than light information transfer: to extract the particle stat one has to perform a measurement which immediately destroys the state it is in.
It is unlikely that quantum entanglement allows FTL signalling of any kind. I also believe it is accepted among physicist that it doesn't allow actual FTL communication.
The classic EPR experiment run thus: magically create a pair of entangled photons, send them in opposite directions. Have them pass through polarised filters of the same direction. Now, the instant a scientist on one side see the photons pass through the filter, she knows the photon on the other side won't get through (and vice-versa). You will notice that the photons don't travel faster than light. So, the obvious explanation will be some kind of common cause. A "hidden variable", that will kinda determine in which direction the photons goes through.
Turns out, there is no hidden variable (Bell's Theorem). So, FTL? Not yet: there may be a third alternative: Many Worlds. Remember Schroedinger's cat? Well, after the experiment, there are two of them: the dead one, and the live one. (No, you don't get to see the other cat, just like your other self doesn't get to see yours.)
Likewise, in the EPR experiment, the scientist merely learn in which blob they are. Though I believe we don't know exactly how decoherence works in this particular case. I'd be surprised however if it actually involved something as complicated as wormholes, or even another dimension.
It says it does travel faster than light - instantaneously. He's just saying that according to Einstein's theory (nothing is faster than the speed of light), that shouldn't happen.
The "nothing faster than light" thing has been repeated so much that people just take it verboten. Its actually not specifically true.
Electromagnetic fields can only propagate through a vacuum at roughly a max of 299,792,458m/s.
Its super easy to slow light down. Sunlight does not travel at its max speed when it hits the ground. Its been slowed down by the atmosphere.
The one thing that most definitely can, and has travelled faster than 299,792,458m/s is space itself. Indeed, space is expanding as we speak.
You only have to worry about causality and referential frame violations if you physically are trying to move at high velocity. Wormholes are shortcuts through points in space. Its a different part of physics that doesn't get into the whole "faster than light" thing. Just sidesteps around it.
