comment by Mitchell_Porter ·
2017-05-25T09:29:48.951Z · LW(p) · GW(p)
Suppose there's some idea, X, which you think might help to solve a problem, Y. And there's also a dumb version of X, X', which you know doesn't work, but which still has enthusiasts.
And then one day there's a headline: CAN IDEA X SOLVE PROBLEM Y? Only you find out that it's actually X', the dumb version of X, that is being presented to the world as X... and nothing is done to convey the difference between X' and the version of X that actually warrants attention.
That is, more or less, the situation I find myself in, with respect to this article. I wish there were some snappier way to convey the situation, without talking about X and X' and so on, but I haven't found a way to do it.
Problem Y is: explain why quantum mechanics works, without saying that things don't have properties until they are measured, and so on.
Idea X is, these days, usually called Bohmian mechanics. To the Schrodinger equation, which describes the time evolution of the wavefunction of quantum mechanics, it adds a classical equation of motion for the particles, fields, etc. The particles, fields, etc., evolve on a trajectory in state space which follows the probability current in state space, as defined by the Schrodinger equation.
The original version of this idea is due to de Broglie, who proposed that particles are guided by waves. This was called pilot-wave theory, because the wave "pilots" the particle.
Pilot-wave theory was proposed in the very early days of quantum theory, before the significance of entanglement was properly appreciated. The significance of entanglement is that you don't have one wavefunction per particle, you just have one big wavefunction which provides probabilities for joint configurations of particles.
A pilot-wave theory for many particles, in the form that de Broglie originally proposed - one wave per particle - contains no entanglement, and can't reproduce the multi-particle predictions of quantum mechanics, as Bell's theorem and many other theorems show. Bohmian mechanics can reproduce those predictions, because in Bohmian mechanics, the wavefunction that does the piloting is the single, entangled, multi-particle wave used in actual quantum mechanics.
All this is utterly basic knowledge for the people who work on Bohmian mechanics today. But meanwhile, apparently a group of people who work on fluid dynamics, have rediscovered de Broglie's original idea - "wave guiding a particle" - and are now promoting it as a possible explanation of quantum mechanics. They don't seem to care about the theorems proving that you can't get Bell-type correlations without using entangled waves.
So basically, this article describes the second-rate researchers in this field - in this case, people who are doing the equivalent of trying to force the square peg into the round hole - as if they are the intellectual leaders who define it!