If quantum mechanics forbids trajectories, what do we see in bubble chambers?

[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?

 

[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.

 

[ChrisVer]

thanks!

 

[Demystifier]

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?

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.