Quantum Entanglement: Is Spin Truly Random?

[ryuunoseika]

Correct me if I'm wrong, but it seems to me that if you split a particle separate the parts and measure their spins only to discover it's always the opposite except when tampered with, that's a sign that said particle's spin isn't truly random and is actually part of some complex algorithmic pattern that happens to be the same in the two particles, not that the two particles are somehow communicating instantaneously. Am i wrong?

 

[cesiumfrog]

That would make sense, apart from a further complication which has to do with the violation of "Bell's theorem".

 

[Ilja]

Correct me if I'm wrong, but it seems to me that if you split a particle separate the parts and measure their spins only to discover it's always the opposite except when tampered with, that's a sign that said particle's spin isn't truly random and is actually part of some complex algorithmic pattern that happens to be the same in the two particles, not that the two particles are somehow communicating instantaneously. Am i wrong?

A complex algorithmic pattern which is the same for the two particles would be a local realistic explanation. Such an explanation cannot be used for an explanation for the violation of Bell's inequality.

See http://ilja-schmelzer.de/realism/game.php" for the slightly more complicate situation which cannot be explained in this way.

 

[Count Iblis]

It could perhaps work if you assume that the observer is deterministic too and is also part of the algorithm that describes the spins. Then any counterfactual choice of the observer for the setting of the polarizers don't exist and Bell's theorem does not apply because of this so-called "superdetermism" loophole.

This has been argued by 't Hooft. He has argued that keeping everything the same except for the settings of polarizers is unphysical in a deterministic theory. If the universe evolved from some fixed initial conditions to a state in which you are finding yourself measuring spins of entangled particles and have decided to set the polarizers in a certain way, then the hypothetical state in which everything is exactly the same except for the setting of the polarizers, cannot have evolved from that initial condition.

In fact, we can be almost sure that evolving such a state back in time will not yield the big bang, but instead, under the inverse time evolution the universe, it will start to effectively evolve forward in time, in the sense that the entropy will increase. The counterfactual state will be a local minimum of the entropy; evolve it forward or backward in time, and the entropy will increase.

The only way to get a bona fide counterfactual state in which the settings of the polarizers is different, would be to find another initial condition out of a set of "physically acceptable initial conditions" which, when evolved forward in time, would yield the desired counterfactual state.

But this then necessarily implies that many other degrees of freedom are different as well in any such counterfactual state.

 

[ryuunoseika]

k, i get it now.