I was thinking (after misinterpreting and answering another question) about collisions on the atomic scale. I know it's impossible to visualize, but I did. For example the collision between an electron and a heavy atom. There are infinite ways the electron bounces of, dependent on the energies of both and their relative momenta.

But then I thought: How many atoms (assuming they can form a whole), packed in space(time), are needed to bounce off another package of atoms, to make the collision classical?

To put it in other words: chances are no longer involved, so the collision becomes non-quantum mechanical, i.e. classical. Within the framework of non-relativistic QM.

I guess this is the same as asking when quantum mechanics becomes classical (it's a blurry line, I guess again, which divides the two). And maybe somehow this has to do with quantum decoherence (see the picture below), but I'm a bit lost here. So..

quantum vs classical

  • $\begingroup$ "chances are no longer involved, so the collision becomes non-quantum" apologies if I am misinterpreting your point, but how can chance be eliminated in either realm? Surely the line between classical and quantum will always be an arbitrary one, dependent on measurement, as you imply above. $\endgroup$ – StudyStudy Jan 23 at 10:38
  • $\begingroup$ Well, Quantum Mechanics is inherently probabilistic and Classical Mechanics (in theory; in practice though you can only make probability predictions, e.g. weather predictions or on which side a flipping coin falls) is deterministic. $\endgroup$ – descheleschilder Jan 23 at 12:05
  • $\begingroup$ hopefully someone better than I can answer your question. $\endgroup$ – StudyStudy Jan 23 at 14:45

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