Many minds : interpretations of QM

[humanino]

Only three choices are selected in the poll, because otherwise too many options would be needed. Those reflect the main different interpretations in my understanding, while minor subtleties might be preferred by some physicists. Please vote for your favorite.

The main difference between one and two is that Bohm allows to consider that the trajectory is well-defined.

Feel free to discuss your adjustements or own tastes.

If you prefer hidden-varaible theories, or other exotic stuff, you can still display it, but please everyone keep it as short as possible.

 

[vanesch]

Hi,

I voted 1, although of course with some caution. I don't know enough about Bohm's theory to consider it. I have to say that if you would have done your poll a few months ago, I would surely have voted 3 (MWI), but since I've been looking deeper into it, it occurred to me that MWI cannot reconstruct the Born rule of probabilities without somehow assuming it. So now I'm convinced (until I change my mind again :-) that the projection postulate is an essential ingredient of unitary quantum mechanics. I'm trying to write a paper on that issue in fact.

cheers,
patrick.

 

[humanino]

Wow Patrick ! I hope you can give us a link to arXiv soon (^_^)

 

[meteor]

All the interpretations suffer from some caveats, and I'm convinced that the correct interpretation is still to come; in MWI I don't understand why my consciousness appears to be continously in one single brain, and I don't experience what the other brains of me experience when decoherence into multiple worlds occur. In Bohmian mechanics I never understood the origin of the quantum potential guiding the motion of particles, (plus this interpretation violates relativity). Wigner's interpretation is too much anthropocentric. So, I'm going to pick Copenhaguen interpretation "because there's nothing better"

 

[slyboy]

I voted other. In my view, an interpretation of quantum mechanics should pick out something to be ontological (i.e. real) other than simply the results of measurement interactions. It should then explain how QM is a probability theory for those ontological objects, preferably in a way that is well-motivated by physical principles. Copenhagen fails to do the former, and de-Broglie Bohm and Many-Worlds fail to do the latter in my opinion.

I don't have an interpretation to recommend at the moment, although I am playing with Huw Price's ideas about backwards causation.

 

[humanino]

backwards causation.

Although Feynman got his little drawings after thinking about that kind of stuff.

 

[slyboy]

To play devil's advocate for the many-worlds interpretation, here is their explanation for why you don't feel that you are in a superposition state of many copies of yourself.

Suppose you measure a spin-1/2 particle in the z-basis, where the particle was initially in the state a|up> + b|down>. After the measurement, if we include the state of the measuring device and your brain in the description we will have:

a|up>|MD shows "up" outcome>|"I saw the up outcome"> + b|down>|MD shows "down" outcome>|"I saw the down outcome">

Now, someone asks you to write down on a piece of paper whether you have split into two copies of yourself or not. Obviously, if b=0, we should end up with:

|up>|MD shows "up" outcome>|"I saw the up outcome">|"I have not split" written on paper>

Also If a = 0 we should get

|down>|MD shows "down" outcome>|"I saw the down outcome">|"I have not split" written on paper>

But in the MWI, every process is linear (i.e. it obeys the Schroedinger equation so it is unitary), so in the general case we get:

a|up>|MD shows "up" outcome>|"I saw the up outcome">|"I have not split" written on paper> + b|down>|MD shows "down" outcome>|"I saw the down outcome">|"I have not split" written on paper>

so you can never be aware that you have been split into two copies without violating the linearity of QM. Of course, to people who do not buy the MWI, this just demonstrates that measurement is a nonlinear process, but if you think that there is nothing special about measurements and every interaction in the universe is unitary then it is a convincing argument.

 

[humanino]

See the lecture on decoherence in [thread=43517]this[/thread] thread. There is no argument in the pervious post, except that the superposition should occur in different "worlds" of the MWI, which is wrong.

 

[Eh]

What exactly was the many minds interpretation about, anyway?

 

[juju]

I voted other.

In my interpretation the wave function and attendant superpositions describe a real world condition. This can be seen as a connected field whose properties are distributed within the field as specified by the wave function.

The collapse of the wave function is then caused by the relative strengths and asymmetries of the field's interaction with the various portions of the measuring system.

I also believe that the only time that properties are "quantized" is during an interaction of sufficient strength and asymmetry.

juju

 

[CharlesP]

I heard that the Copenhagen interpretation is obsolete. There is no element of subjectivity in quantum mechanics and no need for an observer. Wave functions collapse when an interaction occurs, not when some monkey finds out about it. Uncollapsed superpositions have been observed and the photographs posted in magazines. None of this means that I feel confident in this subject.

 

[seratend]

Well, I prefer not to vote and rather give my personal comment (at least to call for other comments ).
I still have not understood why one wants to have a single “interpretation” concerning QM interpretations.
My main problem with the QM interpretations concerns the “many words” used within the interpretation itself that usually displace the physical problem towards philosophy or metaphysics rather than focussing on "concrete" physics. Currently, I cannot see what usable information a peculiar QM interpretation can bring to a physicist (except for an equivalent mathematical model).

When we use the Newtonian mechanics, we have not such questions (at least myself ). Have you been questioning the possible statistical Newtonian mechanics interpretations?
I do not think so.
However, with statistical Newtonian mechanics we can build the same vote for the possible interpretations: MWI, de brooglie Bohm, orthodox or Copenhagen. All the philosophical content of these point of views are possible. Is it possible to make such a vote?
Nevertheless, today, not many people (I know) seem to be concerned by the interpretations of the statistical Newtonian mechanics. Moreover, I cannot see the physical information such an interpretation can bring to Newtonian mechanics (may be I am too short minded).

In addition, when we remove the interpretation philosophy, all the proposed interpretations rely on the postulates/assumptions of QM:
** unitary state system evolution
** born rules: given an input state, we have a probability “p_out” to get an output state.
** The experimental results: I call it the experimental result postulate and it is usually called “projection postulate” of “collapse postulate”. This assertion explains the results of an experiment (what an observer can see/measure).

It is mainly the last point together (with the born rules) that is subject to interpretations. However as far as I have searched, no one of these interpretations try to explain (with testable experiments) the born rules and/or the experimental results. Consequently, I wonder what a particular interpretation can bring to my knowledge of physics.

Let’s take the de Brooglie Bohm (DBM) theory as an example:
DBM is by construction an equivalent mathematical model of QM but with its own interpretation/philosophy. The DBM interpretation statement “q(t) describes the path of a bohmian particle” is non testable (included in the principles of DBM model). It is thus a philosophy to believe or not on the “reality” interpretation of the bohmian particle, that has no impact on the testable results of QM: No new testable information is brought by this interpretation.
If we follow this philosophy (the reality of the bohmian particle), we will say that there exists a faster than light quantum potential while if we reject this interpretation we have no FTL potential. In this peculiar aspect, this interpretation consequence is almost analogue to the interpretation of the electromagnetic field in the coulomb gauge: Is the electric coulomb potential V(r) a FTL signal or not? Well, depending on the interpretation, consistent with the Maxwell equations, we want to give we can say yes or no without changing the physics or the special relativity content (Lorentz invariance).

So, I return to my question: what sort of usable information a peculiar QM interpretation can provide (except for equivalent mathematical models). If it is the physical explanation of the experimental results (the projection postulate), I prefer to say it is the scope of the decoherence program (as long as we do not mix philosophy with the results).

Seratend.

P.S. For the physical explanation of the born rules (the source of statistics in QM), I currently do not know if there is any interesting results available.