This is one of the weird things about quantum theory (QT). Quantum entanglement has been experimentally verified, so there is no question that it happens. There have been 3 suggested explanations for how it happens. None of the 3 is particularly probable, but experiments have been performed that invalidate all 3 individually. Last year an experiment was performed that invalidated 2 of them at the same time. But it is highly improbable that the remaining one is true, especially since it has been invalidated by itself. People are still working on it and hope to come up with an experiment that invalidates all 3 explanations at the same time.
In 1935 Albert Einstein, Podolsky, and Rosen wrote a paper (the EPR paper) about entanglement in which they explained it away using one of the 3 explanations. The EPR paper has become a very highly cited paper in QT. In the 1960s somebody showed that that explanation was not satisfactory, so that explanation is no longer considered valid. Einstein himself didn't like entanglement, calling it "Spooky action at a distance". But quantum theory calls for it and in the 1970s the first experimental proof was found.
Yes it is a bit of a problem. It does seem to require communication between the entangled particles that is faster than light speed. As far as I know there is no theoretical explanation of how it works, other than the fact that QT calls for it. It is just one of those things about QT that will drive you crazy if you really try to comprehend it.
I have a pretty good book about entanglement "The Dance of the Photons" by Anton Zeilinger The book was written in German, and was translated into English last year.
Bill Gill
