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Did any scientist did experiment to prove that current measurement changed the past?

  1. Aug 20, 2009 #1
    Did any scientist do experiment to prove that current measurement changed the past with time stamps on both current and past events?

    I mean with clear time stamps showing the the past event happened earlier(as proof from a strick time stamp), and it must not be possible to happen if the present measurement (as proof from the same system's time stamp that happened after the past event) is not done.
     
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  3. Aug 20, 2009 #2

    DrChinese

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    Re: Did any scientist did experiment to prove that current measurement changed the pa

    Not sure if you are familiar with the Delayed Choice Quantum Eraser experiment, this may be the kind of thing you are referring to. See for example:

    http://grad.physics.sunysb.edu/~amarch/ [Broken]

    See "Delayed erasure" near the bottom.
     
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  4. Aug 20, 2009 #3
    Re: Did any scientist did experiment to prove that current measurement changed the pa

    But the delayed choice experiment does not change the past. No experiment (yet) changes the past.
     
  5. Aug 20, 2009 #4
    Re: Did any scientist did experiment to prove that current measurement changed the pa

    How do you imagine such experiment? If we had event A, then after experiment we would change the past so we got B instead. When we changed the past, we had also changed all related events, including our memories. So we would remember getting B, not A, in the very first time.

    So even if such experiment succeeds, we would never know it :)
     
  6. Aug 20, 2009 #5
    Re: Did any scientist did experiment to prove that current measurement changed the pa

    Wheeler had a delayed-choice thought experiment where you decide to measure a photon whose wave is split in several paths by gravitational lensing. (gravitational lensing has inded been observed)
    If you decide to measure which way it went through you get one path or the other. If you don't measure which-way then you get an interference pattern, which could be interpreted as the photon going through both paths. This experiment is described in "Law without law". But this is a very long article that gets into a long philosophical discussion. However, the experiment is described in the first pages.
    I think this experiment may not be very useful to favor one interpretation or another because it deals only with photons which according to the CI people are not a particle until it is detected.
    Now, this is just a thought experiment. But it looks that Cramer at the University of Washington has been working on a work-bench experiment inspired in Wheeler's idea that he thinks can "transmit information into the past". Most people think that there must be some flaw in his reasoning and that the experiment will not succeed. It looks that a first version of the experiment was already done by one of his students, but although the data seem to confirm the kind of result that he expected, many think that the use of a coincidence counter in that experiment could explain the interesting results and therefore invalidate the experiment as a proof of what he is trying to demonstrate. Cramer has gotten some financing for a new experiment that would not use the coincidence counter.
    I don't have the links to this information but you can google it. If anybody is interested and needs help finding a link please let me know.
     
  7. Aug 20, 2009 #6

    DrChinese

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    Re: Did any scientist did experiment to prove that current measurement changed the pa

    That's the thing, the DCQE *appears* to change the past. In that situation, your future choice affects my present. The catch is that is not evident from my side alone. It is only evident when correlated with your future choice.
     
  8. Aug 20, 2009 #7
    Re: Did any scientist did experiment to prove that current measurement changed the pa

    The situation is time-symmetrical. That's an EPR experiment with measurements separated by a time-like interval.

    Usually, it is interpreted in the backwards time direction rather than in the forward direction, but the forward direction is exactly equivalent.

    In an EPR experiment with Alice and Bob, you can say that Alice collapses Bob's wave packet, or the opposite, and if Bob chooses to set his device perpendicular to Alice's (for spin 1/2 measurement), there is no correlation.

    In the quantum eraser, it is the same. You can say that the eraser's output collapses the screen's photon wave packet (strange, but effective "future-to-past" way of seeing things), or that the screen collapses the eraser's photon wave packet (much more intuitive, "past-to-future" point of view, though of same effectiveness). And if the second photon doesn't reach the eraser, there are no correlations.
     
  9. Aug 20, 2009 #8
    Re: Did any scientist did experiment to prove that current measurement changed the pa

    thanks. i believe i find a way to test it, and show with clear time stamp whether past event was created by current measurement. I will develop it in the weekends
     
  10. Aug 20, 2009 #9

    DrChinese

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    Re: Did any scientist did experiment to prove that current measurement changed the pa

    Not exactly, in the DCQE. The choice to create an interference pattern - or not - is made AFTER the other side is recorded. So that is not exactly symmetrical. On the other hand, the similarity is that this is only revealed via correlations, not by the actual image either Bob or Alice sees.
     
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