OK Corral: Local versus non-local QM

[Ontoplankton]

Applying Occam's Razor to QM produces an 'instrumentalist interpretation' which is explicitly uninterested in anything untestable, and, instead simply predicts probabilities of experimental results. In other words, as long as there are prediction equivalent theories without a physically real wavefunction, Occam's razor tells us there isn't necessarily one.

I disagree. A wavefunction is a much simpler thing than the collection of all humans and their experiments. Occam would tell you to derive the latter from the former (as in MWI) rather than somehow taking it as given.

 

[NateTG]

I disagree. A wavefunction is a much simpler thing than the collection of all humans and their experiments. Occam would tell you to derive the latter from the former (as in MWI) rather than somehow taking it as given.

Well, ultimately, it comes down to what 'simplest' means. And that requires some sort of arbitrary notions.

 

[Ontoplankton]

I don't know... it's easy to specify a wavefunction; you just write down some equations, and then without any complex further assumptions, you can talk about decoherence and so on to show that humans and their experiments are structures in the wavefunction. But how do you specify the collection of humans and their experiments, without deriving it from something more basic? I think any theory that's anthropocentric like that is bound to violate Occam.

 

[NateTG]

We have one theory which says that:
1. We can predict experimental results using some method X
2. There are things that are not observable used in X.
3. These unobservable things have physical reality.
And another theory that says:
1. We can predict experimental results using the same method X.
2. There are things that are not observable used in X

Even considering that 'physical reality' is a poorly defined notion, it seems like the latter theory is simpler.

 

[Ontoplankton]

The crucial difference here being that in the former theory, 1 is explained by 2 and 3, whereas in the latter theory, 1 is an assumption that comes from nowhere. Occam is bothered by complex assumptions, not complex conclusions. Once you've explained something, you can cross it off your list of baggage.

Also, the latter theory isn't complete; either the unobservable things exist or they don't, and you have to pick one.

 

[Mentz114]

1. We can predict experimental results using QED.
2. The 4-potential $$A^{\mu}$$ is unobservable.

Surely we don't have to make a choice, but rely on experiment ?

 

[akhmeteli]

I disagree. A wavefunction is a much simpler thing than the collection of all humans and their experiments. Occam would tell you to derive the latter from the former (as in MWI) rather than somehow taking it as given.

Actually, it is quite possible that you can do without a wavefunction (I guess Occam would be happy) In http://www.arxiv.org/abs/quant-ph/0509044 , the Klein-Gordon-Maxwell electrodynamics is discussed, the unitary gauge is chosen (meaning the wavefunction is real), and it is proven that one can eliminate the wavefunction from the equations and formulate the Cauchy problem for the 4-potential of electromagnetic field. That means that if you know the 4-potential and its time derivatives at some moment in time, you can calculate them for any moment in time, or, in other words, the 4-potential evolves independently.