Re: Interpreting Quantum Mechanics

Robert wrote:
I would like people who take physics seriously (no Usenet crackpots, please, you know who you are) to comment on the following eight ways that it is possible to interpret quantum mechanics. In both a famous article and book ("Quantum Reality" Nick Herbert discusses eight now well-know ways of interpreting QM.

I haven't read this book, but I warn you that it's probably highly inaccurate. Accurate and informative physics books rarely become popular. The popular books are the ones that read like science fiction, and for the most part are.

Are there any totally new ideas, i.e. interpretations of QM that don't fit into any of these eight ideological boxes?

If Herbert actually implies that these "eight ideological boxes" represent an accurate classification of QM interpretations, then that's a good example of the inaccuracy I predicted above. It's not a sensible classification at all.

I would divide interpretations into three somewhat fuzzy categories. In the first category are mathematically rigorous reformulations that give some insight into the structure of quantum mechanics and suggest possible reasons why quantum mechanics might "have to be true". Some examples in this category are many worlds, quantum logic, and Bohm's pilot wave. In the second category are interpretations that want to be in the first category but aren't there yet, like Penrose's ideas. In the third category are la-la land ideas like "observer-created reality" that have no physically or mathematically meaningful content at all.

Are there any experiments which most physicists agree can, or at least in principle could, show us which interpretations are more true?

Some of the interpretations clarify the question of what exactly constitutes a measurement, and to the extent that they clarify it in different ways, it might be possible to test them against each other. I'm not too hopeful, though.

Many people talk about decoherence as a solution to the question of how a wave function collapses. Assuming that this idea is tenable (or possibly certainly true) would this favor any of the following interpretations, be neutral to all of them, or perhaps suggest yet a different interpretation of QM?

Decoherence is broadly accepted as mathematically correct and physically real, so the fact that all the of usual interpretations have survived means that at least their adherents don't think that decoherence has changed anything.

Nick Herbert talks about "Quantum Reality":

Quantum Reality #1 The Copenhagen Interpretation [...]

As described here, meaningless. But I don't think this is the Copenhagen interpretation. In fact, I don't think there is a Copenhagen interpretation, as such. These days the people who say that they subscribe to the Copenhagen interpretation are the people who aren't interested in the whole debate.

Quantum Reality #3 - Reality is an undivided wholeness. 

Meaningless.

Physicist David Bohm of London's Birkbeck College has especially stressed the necessary wholeness of the quantum world...

Indeed he did, but fortunately his pilot wave ideas had enough mathematical content to qualify as a meaningful interpretation. In the context of his mathematical results, I can sort of understand what he meant by "wholeness", even if I don't agree. The same is true of Bohr and Wheeler and so on. Their comments make some sense in the appropriate context; otherwise, they're meaningless.

Quantum Reality #4 The many-worlds interpretation. [...] In order to
> accommodate different outcomes
without contradiction , entire new universes spring into being, identical in every detail except for the single outcome that gave them birth.

Not an accurate description. The point of many worlds is that there's a mechanism that leads to the worlds, and the mechanism is present in standard quantum mechanics -- you don't have to add it.

Quantum Reality #5: Quantum logic (The World obeys a non-human kind of reasoning.)

There's nothing non-human about quantum logic. It's just non-classical, which simply means that it is not classical logic, classical logic being a certain kind of logic that happens to be particularly well studied.

Quantum Reality #6. Neorealism (The world is made of ordinary objects.) 

Meaningless.

Chief among neorealist rebels was Einstein, whose passion for
realism pitted him squarely against the quantum Orthodoxy...

Not true. Einstein's debate with Bohr was not about interpretations of QM; it was about the logical consistency of the theory. Einstein lost the debate because he was wrong: QM is logically consistent. If it had been a matter of interpretation, the debate would never have been settled.

Einstein was indeed bothered by the fact that QM didn't make sense. /Every/ physicist is bothered by this. They all want to understand what QM is really about.

Quantum Reality #7 Consciousness creates reality... 

Meaningless.

...Eugene Wigner...comments on this ironic turn of events: "It is not possible to formulate the laws of quantum mechanics in a fully consistent way with out reference to the consciousness . . .

This is true only inasmuch as no physical theory can be formulated in a consistent way without reference to our senses, hence to consciousness. It's not any more true of quantum mechanics.

Quantum Reality #8. The duplex world of Werner Heisenberg (The world is twofold, consisting of potentials and actualities.) 

Meaningless.

-- Ben
.

Relevant Pages

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