Where does a quantum experiment *begin*?

[atyy]

It's not in the Hamiltonian, because you choose not to describe it, but take the functioning of the measurement device for granted. Of course, as long as a theory (here relativstic local QFT) is not known to have limits of applicability (which for sure it has, but it's not known yet), I've all reason to believe that also the interaction between the measured object and the measurement device is ruled by the laws described by the theory. Hence, this interactions are the very same local interactions used in the Hamiltonian.

E.g., to describe the creation of a polarization-entangled photon pair with (in-medium) QED, you have to make a model Hamiltonian (as done by Hong and Mandel in the mid 1980ies) and see whether it correctly describes satisfactorily the observed (statistical!) facts about these pairs (which to my knowledge it does). As long as there is not an experiment showing that the creation of entangled photon pairs cannot be described by these standard QED local interactions, I keep it as the valid description. The same holds true for the theory of photon detection, which are also very well described using the standard local QED interactions.

If you believe that quantum theory makes sense with the Hamiltonian extending to the whole universe and having only unitary evolution with neither hidden variables nor many-worlds or something else, then you are mistaken. Also, you are not using the minimal interpretation.

 

[atyy]

Then let us wait for him to clarify his position.

I always mean it in the update sense. If I mean it in the physical sense, I would be referring to GRW or CSL, and would state so clearly. While I am using standard quantum theory in a quantum forum, I should be entitled to use standard terminology in the orthodox interpretation.

However, the problem is vanhees71 is always bringing interpretation in.

If by local interaction, he means some property of the Hamiltonian, then collapse clearly does not affect the Hamiltonian so it does not even make sense to say that collapse is a nonlocal interaction.

But as you see from his post, he thinks there can be a wave function of the universe with no hidden variables and no many-worlds. This is a big mistake - this is the mistake of Ballentine and Peres.

 

[Demystifier]

I always mean it in the update sense.

So I was right about you.

But as you see from his post, he thinks there can be a wave function of the universe with no hidden variables and no many-worlds. This is a big mistake - this is the mistake of Ballentine and Peres.

I don't think that Peres makes this mistake. Indeed, he claims explicitly that wave function of the universe does not make sense. As far as I can see, Peres is one of rare physicists who uses the orthodox interpretation consistently. (Or can you cite the place where he does make such a mistake?)

 

[vanhees71]

Of course, the "wave function of the universe" doesn't make sense. This I emphasized several times. I think, I stop participating in the discussion here, because obviously I cannot make my standpoint clear, and it's only noise left in this thread. Maybe it's even high time to close it and get back to physics!

 

[DrClaude]

While this was an interesting thread, I think that it has deviated far from its point of origin. This was tagged as a B-level thread, after all!

Thread closed.