[alpineidyll3]

There is no measurement problem. It so happens that most measurement apparatus are macroscopic and at a temperature much higher than the quantum gap of the system being probed. Measurements in qm imply a rotation between systems, and mixture with an incoherent thermal state implies a quantum superposition will lose coherence. Full stop. This is all understood in full, grab any text on non equilibrium quantum dynamics. One can even simulate the collapse process in full detail, and obtain superior agreement with experiments.

If the measurement apparatus is coherent, measurements can be performed without collapse. This was well thought out even within wigner and einstein's lifetimes. c.f. the vaidman bomb detector.

[zeofig]

This is certainly my view as a physicist, although I'm not the greatest physicist by any measure. QM can give us a perfectly clear picture of "collapse", although it's not a trivial matter and it's hard to explain to laypeople. Especially when physics fans have these ideas about ~conscious observers collapsing the wavefunction~, or something.

[Orlanthai]

It depends on what one calls the measurement problem.

This solves the "consistency/small problem", i.e. treating the macroscopic apparatus as boolean is justified.

It doesn't resolve the "outcome problem", i.e. which outcome is selected. Of course if you accept the world is not deterministic this isn't really a problem.

[alpineidyll3]

One could argue even classical mechanics isn't deterministic as we think of it because of chaos, which has fascinating connections with QM. W Hoover (of the Nose-Hoover thermostat fame) did some great work with reversible thermostats exploring the instability of Newtons equations of motion.

[Orlanthai]

I think that's different. Chaos still uses classical probability and the randomness is just ignorance of underlying initial conditions. This is very different from QM.

[alpineidyll3]

You'd be surprised. You should read about many-body localization and the eigenstate thermalization hypothesis.

[Orlanthai]

I have. They still don't make Quantum Theory and Chaos similar. Rather for some systems QM can motivate ergodicity as well as classical chaos can. However that doesn't mean Quantum Probability and Classical Probability are alike simply because they give similar behaviour for certain systems for one specific limit. Their representation theory is completely different.

Chaotic systems don't have a Kochen-Specker or PBR theorem.

[thegabriele]

What do i measure of a quantum system if nothing collapse?

Honest question.

[alpineidyll3]

Measurement is a transfer of a state information from a subsystem 'being measured' to a 'measurement device' caused by an interaction. (ie: a quantum bus is a measurement) Just like in a classical situation, further dynamics can depend on the final state in the measurement device. The only difference is that all measurement states will be involved in the quantum measurement device, and all possibilities of dynamics conditioned on the measurement are explored. At any point in the future the whole chain of events can be collapsed, if the measurement device interacts with a classical incoherent object.