Re: Travelling to a different universe

From: George Levy <GLevy.domain.name.hidden>
Date: Thu, 27 Dec 2001 19:45:32 -0800

Thanks guys for the information. Now I have work on my hands.

George

Brent Meeker wrote
 
>Do a search for "transactional quantum mechanics" and look at Vic Stenger's
>website.

>Brent Meeker

scerir wrote:
>
> > George Levy
> > This is interesting. Is it possible to transmit information from the
> > future to the past? If yes, how would this information be restricted?
>
> This is a very difficult issue, as you can see (example below).
>
> A single particle [the example is discussed in references 4, 2, 1]
> at time t_0 is (preselected) in the state
> |psi_0> = 3 ^ (-1/2) ( |a> + |b> + |c> )
> and at a later time t_f is (postselected)
> in the state |psi_f> = 3 ^ (-1/2) ( |a> + |b> - |c> )
> where |a>, |b> and |c> correspond to the particle being found
> in 3 boxes: A, B and C, respectively. (The N boxes case
> is discussed in reference 3.)
>
> At the intermediate time t_i, where t_0 < t_i < t_f,
> a measurement is performed on the system.
>
> The ABL rule [see reference 5] states that if a measurement
> is performed, at time t_i, on this system, with the above
> preselection and postselection of states, the probability
> for an outcome of either a or b (eigenvalues corresponding
> to find the particle in box A or in box B, respectively) is 100%.
>
> That is to say, the intermediate _measurement_ cannot project
> the initial state |psi_0> onto the state 2 ^ (-1/2) ( |b> + |c> ) --
> particle not found in A -- or onto the state 2 ^ (-1/2) ( |a> + |c> )
> -- particle not found in B --. That's because both states
> are othogonal to the final state |psi_f>. Both states are
> then impossible.
>
> As long as we keep the QM formalism and the ABL rule,
> in each case any particles (which end up postselected)
> are ones which could not have been in any box except
> the one which was opened, be it A or B.
>
> Possible solutions? There are some. In example....
>
> 1. QM formalism is right. There is no paradox. That's real.
>
> 2. QM formalism is right. That's not real. QM does not speak
> of reality.
>
> 3. Counterfactuals. To make a claim about the elements
> of reality of an individual system we have to consider the *physical*
> situation involved in an individual run of the experiment. But here,
> in each run, we have to make a *choice* to measure A or B.
> If we choose A, all postselected particles had to be found
> in box A. If we choose B, all postselected particles had to be found
> in box B. But the property of being, with certainty, in any one
> of those 2 boxes (depending on wich one is opened) cannot apply
> to the *same* *individual* particle in *any* given run of the
> experiment.
>
> 4. We cannot use the ABL rule here [see reference 6], because
> of the counterfactuals.
>
> Regards,
>
> -s.
>
> [1] David Z. Albert, Yakir Aharonov, Susan D'Amato,
> Physical Review Letters, vol. 54, pages 5 - 7,
> (1985)
>
> [2] David Z. Albert, Yakir Aharonov, Susan D'Amato,
> Physical Review Letters, vol. 56, p. 2457, (1986)
>
> [3] Yakir Aharonov, Lev Vaidman
> J. Phys, A-24, pages 2315 - 2328, (1991)
>
> [4] Lev Vaidman
> Foundations of Physics, 26, pages 895 - 906, (1996)
>
> [5] Yakir Aharonov, P.G. Begmann, J.L. Lebowitz,
> Physical Review, 134-B, pages 1410 - 1416, (1964)
>
> [6] R. E. Kastner
> Foundations of Physics, 29, pages 851 - 863, (1999)
Received on Thu Dec 27 2001 - 19:47:27 PST