Measurement in de broglie-bohm theory

cryptist

Hi,
Could you describe the "before the measurement" mechanism in de broglie bohm theory? Is there a real collapse during the measurement? Can we determine the particle's position in its guiding function without disturbing it? Is there any way to calculate guiding function?

Demystifier

The theory of quantum measurements in dBB theory is described in many books and papers. Instead of repeating it here, I think it is better to point to a reference where it has already been done. An easily accessible example is the Appendix of
http://xxx.lanl.gov/abs/quant-ph/020818 [Found.Phys.Lett. 17 (2004) 363]
See also the recent discussion in
http://www.physicsforums.com/showthread.php?t=444233

No.

We can calculate it, but we cannot measure it (without disturbing it).

Of course, by solving the Schrodinger equation.

cryptist

Then, for example in double slit experiment, why the interference pattern disappears when we are measuring the particle? Why it would not reappear when we stop measuring it?
Does the measuring particle effects somehow guiding function? After all it is the guiding function that determines its path right?

Demystifier

Because measurement causes decoherence of the wave function.

Because decoherence is irreversible.

No.

Right.

cryptist

But the measurement affects the path of the particle say electron. Since guiding function determines the path, shouldn't it also be effected? For example in the interference pattern we see that electrons in the screen that cannot be there classically. That means electron's path changes with the act of measurement or by decoherence.

Demystifier

True. But it is important to stress that here "measurement" is a process that refers to the evolution of the WAVE FUNCTION. The change of the wave function then causes a change in the motion of the particle.

No, the wave function is not affected by the particle's path.

True.

cryptist

Then, what is the difference between guiding function and wave function?

Demystifier

In dBB theory, there is no difference between them. They are the same.

cryptist

You said measuring particle is not effecting guiding function. But measurement changes the path, and path is determined by guiding function. Aren't these statements conflicting?

Demystifier

I answered "no" to your question, but your question was slightly imprecise in a linguistic sense.
What I meant is that the MEASURED PARTICLE does not effect the guiding function. But the MEASUREMENT OF the particle does effect the guiding function.

cryptist

Ok, I realized the confusion. That's my mistake. I wanted to say "whether measurement of particle effects guiding function or not?". Ok, I understand now.

Kidphysics

You should say thanks for all the things Demystifier has helped you with.

Demystifier

The pleasure was mine.

cryptist

I did not close the topic, so I want to ask actually some other things after I finished my readings. So, of course I will thank you at the end. However, thank you Demystifier for your explanations so far. :)

cryptist

How this decoherence happens during measurement?

And, what is configuration space?

yoda jedi

dBB is a non collapse interpretation of Quantum Mechanics.



.......‘No collapse’ interpretations avoid the measurement problem by selecting
other sets of observables as determinate for a system in a given quantum state........

http://www.psiquadrat.de/downloads/b...uniqueness.pdf

Demystifier

These are questions for another topic, because they are much more general than dBB theory. Especially the second question. In fact, we already have a lot of threads concerning the first question, so try the search option to find some of them.