BTW, quantum entanglement is absolutely useless for sending information. When you have particles with unknown polarization, looking at one collapses the wavefunction so that the polarization of the other is now quantized. That might be useful... if you knew the polarizations to expect! But the wavefunction collapses in a random fashion (i.e. a percentage of the time it will be polarized one way, and a percentage of the time it will be another, etc.).
Sending a "signal" (whatever your "signal" purports to be) requires that the sender and the sendee both know what to expect (i.e. that the signal is non-random in nature).
For example, let's say you have a machine capable of producing photons that will collapse into entangled states (call them A and B), meaning that if one photon is A, the other must be B. Each time you produce a pair, each photon can be either A or B (and behaves in such a manner that you cannot tell without direct observation... that's the essence and inescapable reality of quantum superposition). When you directly observe the first photon and discover it is an A, then the second becomes a B. However, since you have no way of knowing what either is until you look (thereby causing the collapse and "ending" the entanglement), you have no way of sending a signal with them (because you have no way to modulate whether the particle collapses to an A or B). All you get on either end is a series of random As and Bs.
In other words, quantum entanglement might have a great deal of impact on the the question of Locality, but it has absolutely no use in information transfer.
This is what I was taught when I learned Bell's Theorem in graduate school. However, in the last few years this claim has become controversial.
My understanding (and I was a condensed matter theorist and not an expert on quantum ontology or high energy physics by any means) is that current thinking is that certain kinds of purely quantum information can be transmitted at superluminal velocities.
The rather strong requirement that "information" (one assumes somehow rigorously and suitably defined) cannot be transmitted superluminally, has been replaced with the weaker requirement that whatever effects might be transmitted that could convey deterministic information must be Lorentz Invariant. [In other words, there is no reference frame in which deterministic state information could be seen to be travelling backwards in time.]
The weaker requirement is clearly necessary, or we have far bigger problems in the universe than nolocality; and to my knowledge it is the only one that people concerned with the conceptual philosophy of QM have ever insisted on.
of course it does ~ you know at a minimum if A got there ~
Yes, exactly! This is why I’m stumped as to how this is supposed to work. They know the polarization of the photons they sent out, okay, I can see how they could know that. However, how can they know whether the polarization has changed when the photons come back? If they try to measure it, they may be changing the polarization just by the act of observation.