Talk:Counterfactual definiteness
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You know, I've yet to see a single comprehensible explanation of why it is that Bell's theorem assumes CFD, nor why many-worlds violates it. For that matter, I've only ever seen one good explanation of Bell's theorem and unfortunately it discusses neither CFD, nor many-worlds. http://www.mathpages.com/rr/rrtoc.htm (sections 9.5-9.8)
Kevin Aylward:
According to Leslie Ballentine, Professor at Simon Fraser University, and writer of the text book "Quantum Mechanics, A Modern Development" ISBN981-02-4105-4., Bell's theorem dosnt.
He explains in the above book that, firstly, EPR, *derives* CFD, not assumes it. Second, he points out that H. Strap dispenses with CFD, and still shows that QM violates locality.
Subsequently, other have argued that he still assumes CDF implicitly, however, H. P. Stap further answers these criticisms, but the debate is ongoing e.g http://adsabs.harvard.edu/abs/2004quant.ph..4121S, probably till the end of time.
I, too, have trouble seeing how many-worlds violates CFD. The Elitzur-Vaidman bomb-testing problem is an ideal (and experimentally proven) example of CFD, and (at least in my admittedly uneducated mind) it's quite easy to reconcile that experiment with many-worlds. The many-world interpretation of what happens when the photon winds up at the "C" detector is that, in an "alternate universe", the photon took the other path at the first half-silvered mirror, hit the bomb causing it to explode and thus preventing it from completing its trek. If it couldn't complete its trek, it couldn't interfere with the photon from *our* universe (like it does when the bomb is a dud) and so "our" photon winds up hitting detector C unimpeded. The way I see it, CFD not only doesn't violate many-worlds--it actually strongly implies it.
Furthermore, given that 1994 implementation of the bomb experiment actually proved that macroscopic CFD phenomena exist and the fact that the many-worlds interpretation is still very popular, I would say this is evidence that the two ideas are not at odds--if they were, many-worlds would have fallen out of favor given the concrete evidence supporting CFD. --Lode Runner 20:26, 3 October 2007 (UTC)
