Faster than light communication is not possible. If I measure the polarization of an entangled photon and it turns out to be right circularly polarized. In that instant, dont I know that someone measuring the polarization of the other photon will find a left circularly polarized photon. Surely, I have just gained a piece of information, namely that my friend will see a left circularly polarized photon, and he knows I have the opposite. How is this not transmission of information?
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Richard Coppack
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1Try to come up with an idea using this mechanism that you just explained, to send a "hello" message from one location to another. Obtaining merely a piece of information is not transmission of information. – Paradoxy Aug 10 '23 at 17:37
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3Related: Quantum entanglement faster than speed of light? I think this question has been asked dozens of times on this site. You can use the site’s search box to find them. With more than 225,000 questions here, there are few conceptual questions that haven’t already been asked and answered. – Ghoster Aug 10 '23 at 17:46
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1Does this answer your question? Quantum entanglement faster than speed of light? – Dale Aug 10 '23 at 18:02
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Following off of Paradoxy, the problem with FTL communication is not the entanglement, it is the moving the light in the first place. Sure, you can obtain the information across vast distances seemingly instantly, but the light is still confined to move at speed $c$. – Matt Hanson Aug 10 '23 at 18:05
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Many thanks for the guidance. Its my first time on this site. – Richard Coppack Aug 23 '23 at 17:39
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You can get the same result classically. You don't know fancy entangled photons.
The example is trivial, I have 2 index cards. On one card is written "+1", on the other is "-1." I place at random one card in an envelope and send it to a friend in Japan, I place the other other card in an envelop and send it to you. The instant you open your envelope you'll know exactly what my friend in Japan has.
Can I communicate via this method? No. Why? Because if I perform this procedure many times all I have is a bunch of random results "+1" or "-1". A purely random sequence conveys no information.
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Thank you. A "1 " or a "0" is a piece of information. Our whole binary system is based on that. I appreciate that it wont convey anything useful – Richard Coppack Aug 23 '23 at 17:36