Quantum gravity physics based on facts, giving checkable predictions

Sunday, October 16, 2005

Bohm, Bell and Aspect

Einstein's big error in attacking metaphysics was his religious arrogance in trying to win the battle by force of personality and authority. Einstein wrote Born, 'God does not throw dice.' Einstein also made Born wait a long time for his prize. (Born was even deeper in horses*** than Bohr and Heisenberg, for example developing a crackpot social science of the uncertainty and complementary principles; see the article: The Sokal Hoax: At Whom Are We Laughing?

It is weird that Einstein, who was normally very good with public relations, made such a mistake. However, he was a very polite person at least in public, and did not want to drag physics down into a farce. This is partly why Heisenberg's role in trying to make a bomb for Hitler is ignored. It is harder to ignore Heisenberg's false derivation of the uncertainty principle equation using the thought experiment of a 'gamma ray microscope'. Problem is, gamma rays tend to behave different 'laws' to light rays. Light behaves more like a wave in glass, while gamma rays behave more like particles - being scattered mainly by the Compton effect.

The Schroedinger and Einstein objections to the interpretation of the uncertainty principle equation were inadequate to destroy the metaphysical 'Copenhagen Interpretation'. Schroedinger in 1935 put forward the cat paradox, a cat in a box whose fate is controlled by the uncertain emission of an alpha particle from uranium, which sets off a geiger counter connected to a poison flask which kills the cat. (The whole experiment is basically the issue of what happens to a coin if you toss it and are not allowed to see whether it lands heads or tails.)

Schroedinger's reason for using alpha radioactivity instead of a coin toss was that Gamow had recently used quantum tunnelling theory to relate the energy of alpha particles to the half-life of the atoms emitting them. It was a reasonably good agreement between theory and experiment, so was an early success of quantum theory.

The Bohr-Heisenberg Copenhagen Interpretation implies that the cat remains in a limbo state between life and death until an observer looks in the box. Eugene Wigner later asked what happens if one person looks in the box but doesn't tell anyone else the result (thus 'collapsing the metaphysical wavefunction' to a definite result, or determining which one of the two parallel universes we are in). This person is deemed 'Wigner's friend' and is a separate paradox itself.

Now Einstein, Polansky and Rosen came up with an apparently more scientific argument - although I think it was published a few months before Schroedinger's cat paradox in 1935.

Einstein and the rest, or 'EPR', considered a molecule of two atoms, having zero overall spin. They argued that if you separate the atoms and measure the spin of one of them, even if they are metres apart, you will automatically know the spin of the other using the principle of conservation of angular momentum, since the total spin will remain zero.

This disproves the Bohr-Heisenberg Copenhagen Interpretation. Bohr published a defence which was so obscure and unreadable (see The Sokal Hoax: At Whom Are We Laughing?) that nobody noticed that the pages were out of order in both hardback and paperback reprints!

Years later, when Dr David Bohm was trying (with help from Einstein but fierce opposition from Robert Oppenheimer) to take up Dirac's ether ideas and use hidden variables to explain the Schroedinger wave equation and all the rest of it, Dr John S. Bell (1928-90) came up with a weird idea. Why not actually do the EPR experiment, and settle the matter experimentally?

Bell formulated an inequality to make it scientific. (Unfortunately, the inequality is both obscure and trivial, rather like the formulation of the Michelson-Morley experiment to test for an ether.)

Professor Alain Aspect at the University of Paris tested the Bell inequality, publishing the experimental results in three major PRL papers between 1981-2. What Aspect found is that the spins correlate as Einstein predicted even when several metres apart. Aspect used paired light photons moving at light speed in opposite directions.

Sadly, there are two equally valid explanations of the result: (a) The two photons are 'entangled' metaphysically with infinite-speed (or at least, faster than light speed) communication of information between them, or (b) the Copehagen Interpretation is horses***.

Take your pick. You can choose to believe in a non-causal universe if you want. But that interpretation, (a) has no support whatever from science. On the other hand, explanation (b) is completely consistent with science. So the choice is yours. Go off the religion end, and believe in brainwashing the world with UFOs, parallel universes and ESP if you wish. Or grow up!


At 4:41 AM, Blogger nige said...

Hi folks!

This subject is difficult to write about, with obfuscation of Bell's inequality being used by both sides, for and against causality. I've obviously taken shortcuts with the maths. Here are more details for those who want them:

Aspect used two spin-correlated photons and they were emitted at 90 degree angles not 180 degrees, but this makes no difference to the outcome or interpretation.

Aspect measured spin correlations using detectors of photomultipliers behind rotating polarised filters. Full info:

A. Aspect et al., Experimental Tests of Realistic Local Theories via Bell's Theorem, Physical Review Letters, v47, 1981, p460

A. Aspect et al., Experimental Realisation of Einstein-Podolsky-Rosen-Bohm Gedankenexperiment: A New Violation of Bell's Inequalities, Physical Review Letters, v48, 1982, p91

A. Aspect et al., Experimental Tests of Bell's Inequalities Using Time-Varying Analysers, Physical Review Letters, v49, 1982, p1804

At 4:45 AM, Blogger nige said...

Whoops! The photons are emitted in opposite directions after all! It is just that the polarisation of the photons are 90 degrees different to one another! So if you measure one of the two spin-correlated photons to be 34 degrees from vertical, the other will be 90-34 = 56 degrees...


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