Monday, February 22, 2016

Pushing Bohmian action-at-a-distance

NewScientist mag reports on the latest quantum nonsense:
Quantum weirdness may hide an orderly reality after all

Often brushed aside like a forgotten stepchild, a 64-year-old theory of quantum mechanics may now share the stage with its more well-regarded siblings. If it holds up, it might lend support to ideas that the universe is improbably interconnected across vast distances.

The theory, by physicist David Bohm, has been resurrected after researchers carried out experiments on photons that seemed to support it.

The behaviour of the quantum world has befuddled physicists for nearly a century. “We have had geniuses working on it and we still have a problem,” says Basil Hiley, a quantum physicist at Birkbeck College at the University of London, who worked with Bohm until the latter’s death in 1992.

Unlike the classical world, with its clockwork precision and pleasing predictability, the quantum world is rife with randomness.

The famous illustration is the double-slit experiment: if you fire photons at two slits, our classical intuition expects each to pass through one or the other slit and hit a screen on the other side, making a single mark indicative of its particle nature. But when you try it, the photons create an interference pattern of light and dark bands on the screen, as if each photon behaved like a wave and passed through both slits simultaneously.

The dominant explanation of such behaviour is called the Copenhagen interpretation, which states that the question of whether a photon is a wave or a particle has no meaning until you make a measurement – and then it becomes one or the other depending on which property you measure. The other favoured explanation is the many-worlds interpretation, under which each possible state of the photon becomes manifest in an alternate world.

But in 1952, Bohm suggested that the quantum world only appears weird because we don’t know enough about its underlying reality. Beneath the quantum weirdness, he said, reality is orderly.

“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.
Bohm proposed an interpretation of quantum mechanic. That means that no experiment can prove it any more correct than the Copenhagen interpretation or any other interpretation.

If you want to believe that you are being influenced imperceptibly by something in another Galaxy, then Bohm gives you permission to do that, but no experiment will ever back up that view.

The article goes on to describe some variant of the double-slit experiment anyway, and claim that it is compatible with Bohm's interpretation.
“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.

Sheldon Goldstein, an expert on the foundations of quantum mechanics at Rutgers University in New Jersey, points out that the experiment’s observation of particle trajectories predicted by Bohmian mechanics does not prove that Bohm’s theory on the nature of reality was correct. Such paths can also be explained using other theories, he says.

But Goldstein says there are changes afoot. “After decades and decades, people are taking Bohmian mechanics a little bit more seriously,” he says. “There was a time when you couldn’t even talk about it because it was heretical. It probably still is the kiss of death for a physics career to be actually working on Bohm, but maybe that’s changing.”
No, only crackpots believe in Bohmian mechanics or many-worlds.

These interpretations have some value in showing what interpretations are possible. But that's all. They do not give any better understanding of the world.

If anyone finds evidence of parallel universes or instaneous influences from other galaxies, then we will have to confront that. But lacking such evidence, it is crazy to believe in such outlandish ideas. Believing in ghosts makes much more sense.

The Bohmians would have you believe that quantum mechanics is inexplicably "weird", and is hiding an orderly reality. This is backwards. A world where things in distant galaxies immediatly influence us is not an orderly reality.

The recently discovered gravitational waves took millions of years to get to us. The effect was extremely slight, but getting here immediately would be contrary to ordinary scientific thinking about cause and effect.

The Bohmians want you to throw away such causality. That would be far far weirder than quantum mechanics.

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