Quantum Mechanics: Bell's Theorem

I found this very easy to follow explanation of the Bell Inequality experiment and the profoundly weird conclusions you're forced to draw about reality. It'll take about an hour or so to read through, but it's very straight forward.

Bottom line: When it comes to the more fundamental aspects of the universe you just cannot trust your intuition.

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People have measured entangled photons at really long distances over optical fiber or free space. I think it was in the hundreds of km. Generally, the topic is of academic interest for communications between the pair that may occur faster than the speed of light. I don't know too much about that, but I think there are some arguments on whether or not communication is actually possible or just the ability to affect the other photon. Anyway, I think there is enough belief that I've heard of research going on to make entangled photon sources. :shrug: I think entanglement is the reason why identical twins can sense each other's feelings even if they are separated by thousands of miles because they originated from the same quantum state in the womb. OK, now I'm just being silly...

brucec said:

People have measured entangled photons at really long distances over optical fiber or free space. I think it was in the hundreds of km. Generally, the topic is of academic interest for communications between the pair that may occur faster than the speed of light. I don't know too much about that, but I think there are some arguments on whether or not communication is actually possible or just the ability to affect the other photon.

Click to expand...

Actual transfer of information faster than light would violate general relativity (GR). Entangled "thingies" do however indeed seem to communicate faster than light, but fortunately (for the GR theory) the communicated "data" is random and therefore cannot be used to send actual information. The link I provided explains these things much better than I could ever hope to do.

Talking with a professor who focuses on quantum optics, I can relay a simple explanation explanation of why FTL information cannot work.

We may have particles that are entangled, and they will react instantly to any changes in a way that somehow relate the two. The relationship however is not a perfect mirror or anything helpful, unless you use some other means to correlate the two. To help figure out what is going on, you would need to communicate over some slow channel, hence ruining the speedy process.

I almost liked to think of it as really good cryptography. The entangled particles will react, and they will have a pattern in their actions. However, this pattern is useless without some sort of decoding key, which can only be sent over subluminal methods.