Alice, Alice, Bob, & Bob explain why entanglement does not imply faster than light communication
I just read this article on phys.org which claimed to "resolve the paradox" that entanglement appears to imply faster than light communication. I don't think it actually resolves the paradox, it just side steps it. Here's how the argument goes (and I paraphrase):
Alice and Bob share a pair of entangled qubits in a Bell state $\left( \lvert 01 \rangle + \lvert 10 \rangle \right)/\sqrt{2}$. When Alice measures hers it "collapses" the pair's state immediately even if Bob is a great distance away. However, this does not imply faster than light communication because, although Alice now knows what Bob will measure, Bob does not know until he makes a measurement himself, or receives a message from Alice which can only travel at the speed of light.
This argument misses the point somewhat. If the state of both qubits changes instantly when Alice measures her qubit (e.g from $\left( \lvert 01 \rangle + \lvert 10 \rangle \right)/\sqrt{2}$ to $\lvert 01 \rangle$) then something is travelling at a speed faster than light. It may not be information being communicated from Alice to Bob, but it is an effect of some kind.
To me, the reason this attempt to resolve the paradox fails is that it leaves out the multiverse, and any attempt that ignores the multiverse is destined to fail. So... I thought I'd have a go at explaining it myself, but keeping the multiverse front and centre. Is this cartoon the first to introduce Alice & Bob's identical twins Alice & Bob?
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