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Quantum Experiment Shows Effect Before Cause 465

Posted by Soulskill
from the enjoy-the-headache dept.
steveb3210 writes "Physicists have demonstrated that making a decision about whether or not to entangle two photons can be made after you've already measured the states of the photons." Here's the article's description of the experiment: 'Two independent sources (labeled I and II) produce pairs of photons such that their polarization states are entangled. One photon from I goes to Alice, while one photon from II is sent to Bob. The second photon from each source goes to Victor. Alice and Bob independently perform polarization measurements; no communication passes between them during the experiment—they set the orientation of their polarization filters without knowing what the other is doing. At some time after Alice and Bob perform their measurements, Victor makes a choice (the "delayed choice" in the name). He either allows his two photons from I and II to travel on without doing anything, or he combines them so that their polarization states are entangled. A final measurement determines the polarization state of those two photons. ... Ma et al. found to a high degree of confidence that when Victor selected entanglement, Alice and Bob found correlated photon polarizations. This didn't happen when Victor left the photons alone.'
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Quantum Experiment Shows Effect Before Cause

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  • by NeutronCowboy (896098) on Tuesday April 24, 2012 @05:30PM (#39788001)

    The speed of light is known with a precision that goes quite beyond that. After that, the timing is a simple question of arithmetic.

  • by martin-boundary (547041) on Tuesday April 24, 2012 @06:57PM (#39788867)
    Asimov made shit up, which is very different from prediction.
  • by Killall -9 Bash (622952) on Wednesday April 25, 2012 @12:06AM (#39791243)
    I RTFA, and I didn't like the (lack of) explanation.

    As usual, QM's explanation is saying "uncertainty" very slowly and profoundly. (Slowly for the dim-witted among us, profoundly for the benefit of the Nobel selection committee).

    Seriously. TFA states that the measurements are not literal, and correlation between measurements happens after the fact.

    So: quantum entanglement gives you a way to defeat uncertainty, by letting you measure the mutually exclusive information from a set of correlated particles... Except no it doesn't, because you can't be certain of your measurements.

    And: clever experiments like this let you send information back in time.... Except that no it doesn't, because the universe still has plausible deniability (i.e. you only thought you sent information back in time, but it turns out, the universe was going to do what it did anyway and/or your measurements of what happened are uncertain).

    Congratulations, QM fags. You've found another brilliant way to show how fucking retarded you are.

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