# Quantum trajectories

1. Sep 13, 2014

### ChrisVer

If quantum mechanics don't allow the term trajectory for particles, then what do we see in bubble chambers, or what's the meaning of trying to "reconstruct" particle trajectories within a detector?

2. Sep 13, 2014

### atyy

There was a discussion here https://www.physicsforums.com/showthread.php?t=758778.

stevendaryl pointed out that the problem was treated by Mott.
http://www.ba.infn.it/~pascazio/publications/Particle_tracks_and_the_mechanis.pdf
http://arxiv.org/abs/0907.5503
http://arxiv.org/abs/1209.2665v1

There's also the interesting formalism of continuous measurement.
http://arxiv.org/abs/quant-ph/0611067
http://arxiv.org/abs/math-ph/0512069

Regardless of mathematics, the "uncertainty principle" heuristic I have is that these tracks are wide for a "point particle", so although neither position nor momentum are measured perfectly, the coarse measurement of position doesn't conflict with the simultaneous finer (but still not perfectly accurate) measurement of momentum.

Last edited: Sep 13, 2014
3. Sep 13, 2014

### ChrisVer

thanks!

4. Sep 15, 2014

### Demystifier

In such experiments we really detect the trajectory of a localized wave function. In quantum mechanics the concepts of "wave function" and "particle" are different concepts, but careless writers sometimes do not care to clearly distinguish them.