Deterministic Bohmian Interpretation of Quantum Back in the Game
For those determinists out there, the Copenhagen Interpretation of quantum mechanics has often been seen as a thorn in the side. Actually, over recent years, certain more deterministic interpretations have found more favour. However, not many people were expecting the one of the godfathers of quantum physics to make a late comeback.
David Bohm was a big fan of the hidden variables approach to QM - that we just don't know the full picture (all the variables), and if we did, then we would find that reality really was deterministic at base.
This went out of favour, but according to some physicists, as reported in the New Scientist, this is changing. The New Scientist states:
“It’s a very deterministic description, where all the particles in nature have definite positions and follow definite trajectories,” says Aephraim Steinberg of the University of Toronto in Canada.
Many recent experiments have suggested that no such hidden reality exists. However, they have only ruled out a specific class of theories in which the hidden reality of any particle is local, and not influenced by something far away.
Bohm’s ideas involve non-local hidden reality, in which everything depends on everything. In his universe, something happening in a distant galaxy is influencing you right now and vice versa, however minor the effect.
Take the debate over whether an electron is a wave or a particle. Bohm’s theory says that it’s both: an electron is a particle with a definite trajectory, but this path is governed by a wave upon which the electron rides. The wave can also be influenced by other particles, which in turn changes the trajectory of the electron.
Something called the ESSW thought experiment apparently sounded the end for the theory. However:
Now Steinberg and colleagues have performed the ESSW experiment themselves – and concluded that Bohm is back in the game....
They started with pairs of entangled photons, which are so intimately related that measuring the polarisation state of one affects the polarisation state of the other, no matter how far apart they are. One of each pair was sent into apparatus analogous to the double-slit set-up.
Depending on whether its polarisation was vertical or horizontal, the photon was steered towards either the top or bottom slit. As it traversed the apparatus, the researchers probed its position gently enough to preserve its quantum nature. Each measurement gave only an approximate value, but by tracking a vast ensemble of identical photons, they were able to reconstruct the set of trajectories the photons followed from the slit to the screen....
The team thinks this means that the trajectory of the first photon changed the probe’s polarisation – in line with Bohm’s ideas on non-local interactions. This could resolve the problem identified by the ESSW thought experiment. ESSW thought the problem lay with the photon’s trajectory, but Steinberg and his colleagues showed that the trajectory is real – but the detector is an unreliable witness.
“I’m happy to see this resolution. It restores my taste for Bohmian mechanics,” says Steinberg. “We want to bring it back to its rightful place among all other interpretations.”
Hiley is impressed by the experiment. “It is a new way of looking at quantum non-locality, which vindicates the Bohm position,” he says.
This would certainly be interesting news for those in the determinism / indeterminism debate. Check the NS article for more details, as I have omitted much here. Will be interesting to keep an eye on developments here.
Journal reference: Science Advances, DOI: 10.1126/science.1501466
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