When a particle enters a bubble chamber, its wavefunction collapses and the particle behaves as a classical one. Is it correct?
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$\begingroup$ Depending on which interpretation of quantum mechanics that you subscribe to, this question has many different answers. $\endgroup$– AfterShaveCommented Feb 10, 2023 at 5:15
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2$\begingroup$ This is the subject of an excellent paper by Mott, which predates the idea of wavefunction collapse and describes cloud-chamber tracks using correlated probabilities. $\endgroup$– rob ♦Commented Feb 10, 2023 at 5:37
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When a particle enters a bubble chamber, its wavefunction collapses and the particle behaves as a classical one. Is it correct?
No, it is not correct.
A wavefunction , (a mathematical solution of a quantum mechanical wave equation appropriate to the boundary conditions) describes a particle , or the interactions of the particle, in vacuum. One particle hits one atom, the original wavefunction "collapses" and a new one describes the results of the interaction , in vacuum..
Consider Avogadro's number, which says that there are about $10^{23}$ particles per mole. A bubble chamber liquid has an enormous number of atoms with which the incoming particle can have sequential interactions, each interaction changing the current wavefunction, and that is what you see in a bubble chamber picture.
Here is a picture of a bubble chamber event in ahydrogen bubble chamber where a magnetic field is imposed perpendicular to the page.
The main interaction happens at the vertex on the top. That has the specific wave function which the experiment is studying, i.e. measuring multiplicity, and finding energy and momentum by using the imposed magnetic field.The "collapse" of interest to be studied, and it happens in the microscopic vacuum between the incoming particle and the proton, and the production of new particles is studied.
Look at the pion coming out of the main vertex.Each little dot is a measurement of another wavefunction solution " atom +pion" scattering , a completely different wavefunction than the initial one. Only dots because the interaction is not strong/energetic enough to create quantum mechanically more particles, but enough to ionize the hydrogen and create a dot.
In between each quantum mechanical interaction with the hydrogen of the chamber the negative pion is in vacuum, and because of its charge the momentum it carries bends in the magnetic field in a classical electromagnetic solution, and the track allows to measure the momentum given the mass of the pion from the sequential interactions which create the dots.
