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Thursday, November 16, 2006

Test for quantum "retrocausality" - Going for a blast into the real past

I want to go back to March 13, 1986 and tell myself, "Buy Microsoft!"
""There's a whole zoo of quantum paradoxes out there," Cramer said. "That's part of the reason Einstein hated quantum mechanics."

One of the paradoxes of interest to Cramer is known as "entanglement." It's also known as the Einstein-Podolsky-Rosen paradox, named for the three scientists who described its apparent absurdity as an argument against quantum theory.

Basically, the idea is that interacting, or entangled, subatomic particles such as two photons -- the fundamental units of light -- can affect each other no matter how far apart in time or space.

'If you do a measurement on one, it has an immediate effect on the other even if they are separated by light years across the universe,' Cramer said. If one of the entangled photon's trajectory tilts up, the other one, no matter how distant, will tilt down to compensate.

Einstein ridiculed the idea as 'spooky action at a distance.' Quantum mechanics must be wrong, the father of relativity contended, because that behavior requires some kind of 'signal' passing between the two particles at a speed faster than light.

This is where going backward in time comes in. If the entanglement happens (and the experimental evidence, at this point, says it does), Cramer contends it implies retrocausality. Instead of cause and effect, the effect comes before the cause. The simplest, least paradoxical explanation for that, he says, is that some kind of signal or communication occurs between the two photons in reverse time.

It's all incredibly counterintuitive, Cramer acknowledged.

But standard theoretical attempts to deal with entanglement have become a bit tortured, he said. As evidence supporting quantum theory has grown, theorists have tried to reconcile the paradox of entanglement by basically explaining away the possibility of the two particles somehow communicating.

'The general conclusion has been that there isn't really any signaling between the two locations,' he said. But Cramer said there is reason to question the common wisdom." (full article)
(via cynical-c)

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