# BECs and hidden variables

1. Jul 25, 2009

### maverick_starstrider

Is there a non-local hidden variable theory that accounts for things like BEC's? Did Bahm's original one? Thanks in advance.

2. Jul 25, 2009

### DrChinese

According to standard Bohmian theory, there is equivalence between orthodox QM and Bohmian interpretations. Demystifier is one of our experts on the subject. Check out some of the existing threads that discuss this, such as:

3. Jul 25, 2009

### maverick_starstrider

These threads are very interesting, however I can't say I see how any of these discussions provide a framework/explanation for something like a BEC in a non-local hidden variable theory (although it's possible I missed the relevant discussion). To me, I can not fathom how a non-local hidden variable theory could replicate the experimentally observed predictions/existance of a BEC. Although I'm very curious to read what people have to say on this.

4. Jul 27, 2009

### Demystifier

Maverick, in order to understand how Bohmian interpretation explains BEC, one first need to understand how standard QM explains BEC. Namely, ALL equations valid in standard QM are valid also in Bohmian QM. The ONLY element of standard QM missing in Bohmian QM is the wave function collapse. Instead of the vague concept of collapse, Bohmian QM adds one additional equation that explains how observables take definite values in experiments without a collapse. However, the collapse (measurement) does not play an essential role for BEC's, so Bohmian QM does not say much new about BEC's.

All this means that I do not understand what exactly do you find problematic about BEC's and why exactly do you think that hidden variables might help. So here is a deal. You first explain to me how do you understand BEC in standard QM and what exactly do you find problematic about it, and then I will explain to you how Bohmian QM may help.

5. Jul 27, 2009

### maverick_starstrider

It is rather that I don't see how something like a bohmian interpertation CAN explain coherent phenomena like BEC's that require the wavefunction to be a real thing (at least in every derivation I've seen) and particles to be indistinguishable. Does not the concept of hidden particles with well defined positions destroy that?

6. Jul 27, 2009

### Demystifier

OK, now I think I understand your question. Here is the explanation:
In Bohmian mechanics the wave function IS a real thing. For bosons, this wave function is symmetric under the exchange of particle coordinates. This is just like as that in standard QM.
However, in Bohmian mechanics the wave function is NOT THE ONLY real thing. In addition, there are also pointlike particles with definite positions. This means that particles are indistinguishable on the level of wave functions, but distinguishable on the level of particle positions.

Does it help?