Epistemic view of the wave function leads to superluminal signal

[A. Neumaier]

But how does this "detection event" happen to appear only at one particular coordinate, while the quantum field is spread over the whole screen? I.e. what causes the "wave collapse" on measurement in your way of interpretation?

Presumably the chaoticity of the macroscopic nonlocal observables (field correlations) of the screen, together with conservation of energy. The latter implies that there can be at most one detection event, the former means that it happens at an unpredictable position.

That field intensity is responsible for the firing rate of the Poisson process at one spot of the screen (i.e., the occurrence of detection events) is a local feature described in any textbook of quantum optics, e.g., in Mandel and Wolf.

 

[ftr]

the only thing left of the particle picture is the detection event.

But isn't it that in cathode tube and cloud chamber the charged particles are deflected by the mass/charge ratio,this sounds even weirder to me than EPR if the electrons were all jumbled up yet displayed individuality.

 

[A. Neumaier]

the charged particles are deflected by the mass/charge ratio

The electron field of a cathode ray also has a definite mass/charge ratio. One doesn't need individual electrons for that.

 

[ftr]

There is no consistent relativistic multiparticle theory,

do you mean that there is no consistant QFT bound state, or Dirac multiparticle(>2).

 

[A. Neumaier]

do you mean that there is no consistent QFT bound state, or Dirac multiparticle(>2).

In an interacting relativistic QFT there may be bound states, but one cannot say that these are composed of 2 or 3 particles, say. There are no multiparticle states, since the Hilbert space of a QFT is not a Fock space. See https://physics.stackexchange.com/questions/398200/

This means that interacting relativistic QFTs are field theories, not multiparticle theories. Particles exist only as asymptotic (i.e., approximate, essentially free) states.

 

[MichPod]

Presumably the chaoticity of the macroscopic nonlocal observables (field correlations) of the screen, together with conservation of energy. The latter implies that there can be at most one detection event, the former means that it happens at an unpredictable position.

That field intensity is responsible for the firing rate of the Poisson process at one spot of the screen (i.e., the occurrence of detection events) is a local feature described in any textbook of quantum optics, e.g., in Mandel and Wolf.

But what then prevents a creation of a superimposed state of a screen+electron field where each possible detection event of the electron "happened" with some probability amplitude? We know that a linearity of Shredinger equation in QM does not prevent that to happen yet the measurement postulate demands a collapse to "happen". Then what is different in principle when you consider QFT or your interpretation of QFT? (disclaimer: I do not know qft nor quantum optics and I cannot learn enough just in one morning, so I cannot make any argument, just want to understand briefly how you resolve this problem, if possible).

 

[A. Neumaier]

But what then prevents a creation of a superimposed state of a screen+electron field where each possible detection event of the electron "happened" with some probability amplitude?

In the thermal interpretation, states are described by density operators of the form $\rho=e^{-S/k}$, where $S$ is an entropy operator and $k$ the Boltzmann constant. The notion of superposition becomes irrelevant on this level; one cannot superimpose two density operators. Pure states, where superpositions are relevant, appear only in a limit where the entropy operator has one dominant eigenvalue and then a large gap. For example, this is the case near equilibrium if the Hamiltonian has a nondegenerate ground state and the temperature is low enough. For this one needs a sufficiently tiny system. A system containing a screen is already far too large.

We know that a linearity of Schroedinger equation in QM does not prevent that to happen yet the measurement postulate demands a collapse to "happen". Then what is different in principle when you consider QFT or your interpretation of QFT?

We observe only a small number of field and correlation degrees of freedom. The quantum dynamics coarse-grained to a dynamics of these degrees of freedom is the one we actually observe. This coarse-grained system (at increasing level of coarse-graining described by the Kadanoff-Baym equations, Boltzmann-type equations, and hydrodynamic equations) behaves like a classical, highly chaotic dynamical system. Compare with the Navier-Stokes equations, which are one example of such a coarse-grained system.