Wednesday, September 21, 2011

Physicists bid farewell to reality?

An 18 April 2007 Nature story reports:
There's only one way to describe the experiment performed by physicist Anton Zeilinger and his colleagues: it's unreal, dude.

Measuring the quantum properties of pairs of light particles (photons) pumped out by a laser has convinced Zeilinger that "we have to give up the idea of realism to a far greater extent than most physicists believe today."

By realism, he means the idea that objects have specific features and properties — that a ball is red, that a book contains the works of Shakespeare, or that an electron has a particular spin.
No, there is no evidence at all against realism, with that definition. There is only a problem if you define realism as requiring that the properties of objects be unchanged by observation. For example, you can measure an electron's position, but it will not stay put.
Allied to this assault on reality was the apparent prediction of what Albert Einstein, one of the chief architects of quantum theory, called 'spooky action at a distance'. Quantum theory suggests that disturbing one particle can instantaneously determine the properties of a particle with which it is 'entangled', no matter how far away it is. This would violate the usual rule of locality: that local behaviour is governed by local events.

Einstein could not believe that the world was really so indeterminate. He supposed that a deeper level of reality had yet to be uncovered — so-called 'hidden variables' that specified an object's properties precisely and in strictly local terms.
No, Einstein was not one of the chief architects of quantum theory. He did not believe in it, or even understand it, if he thought that local hidden variable theories were intuitive and plausible alternatives to quantum mechanics. No one has ever been able to make any sense out of those theories.

Nowadays, realism is often mean to imply something like the De Broglie–Bohm theory or Many-worlds interpretation of quantum mechanics. But these theories have bizarre and incomprehensible features that do not seem realistic to me.

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