# Bohmian determinism for aspects other than position?

1. Sep 15, 2014

### georgir

If I got the general idea correctly, Bohmian mechanics is completely deterministic regarding particle positions. But can it also do the same for spin or polarization? How does entanglement work out in it, considering that it should be able to give predictions along any measuring angles, not just the two selected ones?

Edit: On a somewhat related tangent, is it possible to have entanglement and an EPR paradox with position?

2. Sep 15, 2014

### Staff: Mentor

The following will probably help:
http://philsci-archive.pitt.edu/3026/1/bohm.pdf

Thanks
Bill

3. Sep 15, 2014

### Demystifier

Bohmian mechanics is deterministic about ALL observables (including spin), but it is not ONTOLOGICAL about spin. When you perform a measurement which you call a measurement of spin, what you really observe is a POSITION of something (see e.g. how the Stern-Gerlach apparatus work). More generally, all measurements can be reduced to a measurement of position of something. This suggests that particle positions might be the only thing which really exist, and Bohmian mechanics takes this idea seriously.

The original EPR paradox is formulated in terms of positions and momenta.

4. Sep 15, 2014

### georgir

Oh right - cheating the uncertainty principle by using a pair of particles. To be honest, I never understood how that could be interpreted as anything other than implying both properties exist and the uncertainty principle is just BS. How can it ever be interpreted as an effect from one measurement on the other?
Bohmian mechanics, always having a certain position also must have its derivative, and so eliminates the uncertainty principle?

But no, I was not referring to violating the uncertainty principle. Rather, I'm curious about violating some statistical Bell-type inequalities. With properties other than position, which can be said to not exist until measured and to depend on the specific way they are measured, I can more easily see how such violation can be interpreted as "spooky action at a distance" - a dependency on the remote detector and not just the local one. But I guess it was incorrect to call that "EPR paradox". My bad :p

I see your point about such properties ultimately boiling down to position though, so I guess the distinction I'm trying to make is pointless. I'll need some more processing time trying to think about all that.

5. Sep 15, 2014

### DrChinese

You're fine! The EPR Paradox generally means:

"With 2 reasonable assumptions, a more complete specification of a system is possible than QM provides."