Bohm

[sanctus]

I often heard of the Bohmian interpretation of QM,but never exhaustively and I havn't much time to read a book on it.Could anyone just give the outlines? Thanks ver much

[Qfwfq]

You can look it up in reasonable detail at plato, though I found that article a touch biased to the point of giving a few dubious attributions of opinion.

 

Imagine the Young interference example for a single particle at a time. You can find a detailed discussion in Feynman's vol III (QM) which is also a chapter of vol II. He also gives a reductio ad absurdum agument about the idea of saying which hole each particle went through. At the time it had only been done for photons and Feynman discusses it for electrons as a purely conceptual experiment but since then it has been done.

 

According to the Born, or Copenhagen, interpretation it simply makes no sense to say that the particle went through one or the other hole, if there wasn't an interaction that could determine this. Such an interaction would also goof up the interference. According to Born there is no such thing as the position of the particle, before an interaction determines it.

 

According to Bohm, Schrödinger's equation and an extra equation called the guiding wave equation determine a tendency, as the particle goes along, so there is an actual trajectory although it wasn't observed. It views the casuality as being quite like classical chaotic systems. It seemingly cuts out the problem of local causality but it doesn't really get everything matching up.

[sanctus]

Actually the bohm interpretation seems more intuitive, why isn't it teached at all (my prof made once a parenthesis on it that's all), I mean both give the same predictions or not?

[Qfwfq]

What actually makes the predictions is the formalism, including the modulus square rule for probability. This is what is taught, basically. Born, Bohm, hidden variables and any other interpretation are on the borders between physics and epistemology, or even metaphysics, they aren't taught much in physics courses except just to say what the formalism means.

 

For those who go more into these things, hidden variables are not much favoured by most and Bohm goes that way with them. The philosophical arguments are always quite subtle and don't interest all that many physicists.

[sanctus]

hidden variables? Is there still talks about them? Didn't the Bell inequalities show that hypothesis of hidden variables is wrong?

[Bo]

you shouldn't take bell's theorema to literally. As you might know, the basis of the theorem is that you perform two measurements, that both produces two strings of data:

measurement 1: (A,:)

measurement 2: (B,C)

 

now matheaticly the two strings B are exactly the same, there is however nothing that guarantees us that this is also the case in a quantum system.

 

Furthermore you should remember that hidden variables etc. make of QM a predicting theory that can tell us something about a single particle. Standard QM (and also Bell's theorema) can only talk about a long string of data and say something about it's distribution.

 

Bo

[paultrr]

Actually the bohm interpretation seems more intuitive, why isn't it teached at all (my prof made once a parenthesis on it that's all), I mean both give the same predictions or not?

 

Its never been considered as what one could term mainline. It's also true the hidden variables approach is not very popular anymore even though the debate on both still goes on. Between the two I find Bohm's model interesting and know a few people who perfer it. The hidden variables idea in short has its problems, though I have written a few articles that mention it from time to time. As to simular predictions I once used the Bohm model and got a simular dual time aspect to another author who used Bell (her article was published, however I have forgotten eactly where it was published). Before you ask the dual time frame had to do with entanglement. So there are things in common between different views as far as prediction go.

[paultrr]

What actually makes the predictions is the formalism, including the modulus square rule for probability. This is what is taught, basically. Born, Bohm, hidden variables and any other interpretation are on the borders between physics and epistemology, or even metaphysics, they aren't taught much in physics courses except just to say what the formalism means.

 

For those who go more into these things, hidden variables are not much favoured by most and Bohm goes that way with them. The philosophical arguments are always quite subtle and don't interest all that many physicists.

 

I agree and have often thought the same myself when it comes to all of this. If anything they tend to point out the world view some have over others. Both Bohm and the hidden variables approach tend towards putting pure determinism back into the random, so to speak. A lot of us who are scientists, while with most of the modern trend have rejected pure determinism, do have a stubborn tendency like Einstein to favor shall we say, "God not playing dice". Sort of like one of my own favorite reply which is God does play dice. He just uses a loaded set. We like order and I have noticed that some of the more vocal advocates to both Bohm and Hidden variables highly believe in that order. That is perhaps why I have over time myself liked aspects of both approaches. But it is by far not the majority view, nor is it the soundest views out there.

 

I think its safe to say it is epistemology that borders at times on metaphysics that comes into play here.

[paultrr]

hidden variables? Is there still talks about them? Didn't the Bell inequalities show that hypothesis of hidden variables is wrong?

 

You'd think it would have. But it has not totally done away with the other. There are a few hidden variable supporters out there that argue the whole Bell inequalities aspect. One, who's name I will leave out, goes as far to say that entanglement,for instance, is just a mismeasurment of what is actually going on. Some people simply ignore Bell and perfer other approaches.