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Retro causation in weak measurements?

  1. Apr 8, 2014 #1
    I have been working for a while in weak measurements and I have noticed that some physicists such as Aharonov, Vaidmenn or Popescu have suggested that weak measurements reveal some sort of retro causation phenomena. One of the things that confuse me is that they state that when we weakly measure without post-selecting anything, we obtain a list of random variables (none of the values can indicate the state of the system), but if we then make a certain post-selection, then we can "divide" or "split" de data previously obtained, and we will be able to see that the pointer's distributions will be centered around a weak value. In other words, they seem to think on the post-selection as just a way of "ordering" the data obtained during the weak measurement procedure, and then they go to argue that "the information of the future post-selection was already there, in the weak measurements distribution, although we could not see it" (we can see it just once the post-selection is over). This is very strange since I do not understand exactly what is that list of weak measurements, as far as I understand the only list that you could obtain are the results of the experiment, and these results already include the post-selection. It is as if we could, at least in principle, differentiate the weak measurements results from the "weak measurements plus post-selection results", but in practice we could not make this differentiation. In other words, they do not regard the post-selection as part of the weak measurement procedure, but only as a way of organizing the outcomes so that we can better see the information obtain during the weak measurements.
    I appreciate any ideas or any articles that could help me to better understand this allegedly relation between retro causation and weak measurements. Thanks
  2. jcsd
  3. Apr 16, 2014 #2
    The idea is not to have a another predictive method to get results given a set of initial conditions.

    The two state formalism is nearly, but not quit implied if the laws of physics are time symmetric, modulo CP.
    We can always say the state vector evolves unitarily, and so reversibly, and there isn't a need for second state vector--as far as I can see.

    I am by no means an expert at this. However there has been some a difference of opinion explaining something called spurious oscillations. We seem to have two different, and exclusive theories to explain it. This is no small thing as far as I can see; the TWSF serves as an alternative incompatible theory to standard quantum mechanics. I think this is a big deal that has either been overlooked by most, or no one knows where to go with it or resolve it.

    Aharanov talks about two state vectors. One propagates forward in time and the other backward. This in a nice toy model, and is good for making things easier to mentally visualize, but nothing flows or propagates in time. One could just as well swap the two state vectors and say the forward 'propagating' state vector is propagating backwards in time and the backward propagating vector is propagating forward without changing the formalism.
    Last edited: Apr 16, 2014
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