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de Broglie-Bohm has the same problems as usual for such theories. I wrote an article once [0] about such things and I'll just quote from it. > To understand th
by knzhou 7y ago
de Broglie-Bohm has the same problems as usual for such theories. I wrote an article once [0] about such things and I'll just quote from it.
> To understand the working physicist’s position, it is useful to consider pilot wave theory. This alternative to the Copenhagen interpretation is often championed by realist philosophers, who would prefer that measurable properties, such as the position of a quantum particle, should always be well-defined. In this interpretation, the wavefunction is a classical field, like the electromagnetic field, called the pilot wave. Every particle always has a definite location, but it is “guided” by interaction with its pilot wave, allowing it to perform feats impossible for ordinary classical particles, such as quantum tunneling. Hence, the subtlety of quantum mechanics is dispelled by describing a quantum particle as both a classical particle and a classical field, in a literal interpretation of wave-particle duality.
> For those who have struggled with the subtleties of quantum mechanics, this simple story sets off alarm bells. For one thing, where is the probability? If the electron really has a definite position, then why is it measured to be seemingly random, even after the electron settles into its lowest energy state? The answer is that the pilot wave is postulated to unpredictably shuffle about the location of the electron until its position reaches “quantum equilibrium” and matches with the predictions of the Copenhagen interpretation. This shell game is assumed to occur too quickly to detect. Worse, once it is over, the electron is predicted to hover in midair, perfectly still. Velocity measurements indicate otherwise, so pilot wave theory simply assumes they are all mistaken. Apparently, there is a real velocity, but it cannot be measured, and any attempt to do so yields something else. These ad hoc fixes allow pilot wave theory to avoid contradiction with the empirically verified uncertainty principle.
> The pilot wave itself also has strange properties. We expect to be able to measure classical fields, but the pilot wave cannot be directly measured. Classical fields were introduced to avoid nonlocal “action at a distance”, but when the particle is measured, the pilot wave instantly collapses. The collapse is postulated to be faster than light but coincidentally completely undetectable, making pilot wave theory almost impossible to reconcile with relativity. Furthermore, “Bell test” experiments confirm that this problem cannot be removed in any refinement of the theory.
> The reason most physicists are hesitant to accept pilot wave theory is that it appears to have the ether’s flaws. In exchange for the classical intuition of definite particle trajectories, the theory drastically increases the complexity of our world. It suggests many natural questions about the nature of the pilot wave and particle, then gives them unnatural answers which are hidden from observation. That is why, when physicists working on quantum foundations were polled at the 2011 conference Quantum Physics and the Nature of Reality, precisely zero vouched for the pilot wave. The interpretation is like an art teacher who sings the praises of creative freedom, yet berates any who draw outside the lines.
I don't personally have anything against Bohmian mechanics except for one thing: its supporters consistently ignore all of these well-known issues and present it as if it's a completely perfect quasi-classical model for the world, only kept down by conspiracy. This leads to all kinds of crazy narratives that I think are actively harmful to the field. At the very least, people who go out and talk about the many worlds interpretation face the weirdness of quantum mechanics head on, and honestly.
0: https://knzhou.github.io/#writing https://knzhou.github.io/#writing
- lisper 7y agoThanks. That's a great essay. You should put your name on it.
- vincent-toups 7y agoThis is as good a description of the ontological limitations of pilot wave theory as any, but many of the criticisms apply to almost literally any interpretation of quantum mechanics whatsoever. As a physicist with a passing interesting the subject of foundations, its my feeling that what quantum mechanics tells us is that at least one aspect of our classical ontologies is not correct. My personal bet is that its locality which is the problem, but as far as I understand it the question is still wide open. de Broglie-Bohm merely casts the ontological tensions with classical physics in one particular light, but I'm aware of no interpretation which is free of the tension.
- ncmncm 7y agoI thought that locality had had to be abandoned long ago, at least for entangled particles. Of all the oddities pressed on us by alternative interpretations, non-locality between particles that have once interacted seems least troubling. Or is that not enough?
- vincent-toups 7y agoThere isn't any consensus on what aspects of our classical ontology are the right ones to get rid of. You can preserve local realism if you have superdeterminism, for instance.
- deleted 7y ago[deleted]