Sunday, May 30, 2010
Gerard 't Hooft (above) has disputed the validity of Bell's theorem on the basis of the superdeterminism loophole and proposed some ideas to construct local deterministic models.
Superdeterminism is one of a few attempts to show that a local hidden variable theory can reproduce the predictions of quantum mechanics, which if proven, would create a theoretical escape route from Bell's theorem.
Bell's theorem assumes that the types of measurements performed at each detector are chosen independently of each other and of the hidden variable being measured. But in a truly deterministic theory, this would not be the case. Although the experimenters might believe they are making a free and independent choice, their choices are really predetermined by the laws of physics. Since the types of measurements at each detector can be known in advance, the results at one detector can be affected by the type of measurement done at the other without any need for information to travel faster than the speed of light.
Bell acknowledged the loophole, but argued that it was improbable. Even if the measurements performed are chosen by deterministic random number generators, the choices can be assumed to be "effectively free for the purpose at hand," because the machine's choice is altered by a large number of very small effects. It is unlikely for the hidden variable to be sensitive to all of the same small influences that the random number generator was.
Bell discussed superdeterminism in a BBC interview:
There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be.
The only alternative to quantum probabilities, superpositions of states, collapse of the wave function, and spooky action at a distance, is that everything is superdetermined. For me it is a dilemma. I think it is a deep dilemma, and the resolution of it will not be trivial; it will require a substantial change in the way we look at things.