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Get two pieces of paper. In secret write the same number on both papers.

Transfer one paper to the Moon.

Look to the paper which is left at the Earth. Voila! We know what is on the Moon paper.

The papers are entangled in classical world, without any use of quantum mechanics. It is also clear that in this thought experiment we have no faster-than-light transfer of information.

So entanglement can be produced without quantum mechanics.

What is so special about quantum entanglement, that it is spoken about so much?

porton
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    possible duplicate of Quantum entanglement vs classical analogy –  Aug 31 '15 at 13:45
  • Similar title question: http://physics.stackexchange.com/q/54975/2451 – Qmechanic Aug 31 '15 at 13:54
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    I am of the same opinion, that quantum entanglement is a shorthand way of saying "the system is described by a quantum mechanical state function which when operated upon by the operator for an observable gives the value of the observable with a calculable probability ", that is the prior knowledge. I consider all these musings on entanglement navel gazing. – anna v Aug 31 '15 at 13:56
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    @annav Many physicists agreed with you until tests were done (by Alain Aspect and others) of Bells theorem. Entangled particles can break Bell's inequality in a way that no classical system can. The results of these experiments show (pretty categorically) that quantum entanglement is doing something more than "classical entanglement" of the sort described in the question can. – or1426 Aug 31 '15 at 14:14
  • @or1426 Of course it does , it is a probabilistic theory on the observables that is different from the calculations of classical probability. But it is still all about prior mathematical correlations, imo. – anna v Aug 31 '15 at 15:20
  • @annav Yes reading your comment again you're saying something quite different to the OP (which is more or less what my comment was answering). All of (at least experimental) physics is about mathematical correlations. The importance of the Bell result is it ensures that the mathematical correlations are due to relations between the wavefunction (or density matrix) of the system. In particular the correlations have nothing to do with prior correlations in the observables which don't have a value at all prior to measurement. Let alone one which could be correlated with something. – or1426 Aug 31 '15 at 21:49

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