Saturday, November 19, 2011

Quantum action - Pusey's theorem

I'm looking forward to the discussions on this paper by Pusey et al ...

Quantum theorem shakes foundations : Nature News & Comment

... Robert Spekkens, a physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, who has favoured a statistical interpretation of the wavefunction, says that Pusey's theorem is correct and a “fantastic” result, but that he disagrees about what conclusion should be drawn from it. He favours an interpretation in which all quantum states, including non-entangled ones, are related after all.

Spekkens adds that he does expect the theorem to have broader consequences for physics, as have Bell’s and other fundamental theorems. No one foresaw in 1964 that Bell’s theorem would sow the seeds for quantum information theory and quantum cryptography — both of which rely on phenomena that aren’t possible in classical physics. Spekkens thinks this theorem may ultimately have a similar impact. “It’s very important and beautiful in its simplicity,” he says...

Pusey's interpretation is that the wave function models a physical reality. The paper allows, however, that the wave function is a predictive model [1] -- but, in that case, all quantum states are interconnected across space and time, even uncorrelated states.

This ought to be very interesting ...

[1] If you've done basic stats, you have worked with linear regression models that predict systems statistically, but once the system is understood, are found to be weakly related to the fundamental "truth". Sometimes these models do reflect fundamentals, but they don't have to. This is relatively basic math, but it gives me a way to think about statistically predictive models that don't resemble the "true" mechanistic model.

Update: Shtetl Optimized (Scott Aaronson) hates this article, PBR's definition of statistics, and especially Slashdot... (emphases mine)

... There’s an important lesson here for mathematicians, theoretical computer scientists, and analytic philosophers.  You want the kind of public interest in your work that the physicists enjoy?  Then stop being so goddamned precise with words!   The taxpayers who fund us—those who pay attention at all, that is—want a riveting show, a grand Einsteinian dispute about what is or isn’t real.  Who wants some mathematical spoilsport telling them: “Look, it all depends what you mean by ‘real.’  If you mean, uniquely determined by the complete state of the universe, and if you’re only talking about pure states, then…”

Aaronson is a theoretical computer scientist. I don't think he's happy right now.

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