QM Interpretations: Get In-Depth Analysis

[caspiansea3]

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[slyboy]

I'd be interested to know if anyone who voted for the Copenhagen Interpretation can give a coherent explanation of what it actually is.

 

[PRodQuanta]

I'd be interested to know if anyone who voted for the Copenhagen Interpretation can give a coherent explanation of what it actually is.

Basically, an interpretation of quantum mechanics formulated by Bohr and Heisenburg that ended up solving some problems in physics (wave-particle behavior experienced by Michaelson's experiments) by inducing a couple principles, such as the Uncertainty Principle, the instantaneous collapse of the wave function, and the indeterministicism of measurement outcomes, and so on. Very basicly.

Paden Roder

 

[ashfaque]

What about Shahriar Afshar's experiment and the Refuttal(?) of the Copenhagen Interpretation?
Ashfaque

 

[masudr]

As a mathematical physicist, I don't think interpretations matter. Schrodinger's equation will always exist as a fundamental concept of QM. So we can use it! And that's all that matters, in my opinion.

Why don't people worry about an "interpretation" of classical mechanics? People tie themselves up by talking about such an interpretation or another. Instead rely on the equations, they will only fail if QM as a theory is generally a false model.

 

[caribou]

Interpretations can be for removing inconsistencies and gaining deeper understanding but the predictions are usually the same.

The decoherent histories interpretation was created for reasons like to see how the approximation that is classical macroscopic physics emerges from quantum physics and also to remove bizarre things like "external"(!?) observers from cosmology needed to collapse wavefunctions.

I'm studying it to better understand how to think about quantum computation and nanotechnology. Yes, it's all the same predictions but a better understanding is my aim. :)

 

[slyboy]

Basically, an interpretation of quantum mechanics formulated by Bohr and Heisenburg that ended up solving some problems in physics (wave-particle behavior experienced by Michaelson's experiments) by inducing a couple principles, such as the Uncertainty Principle, the instantaneous collapse of the wave function, and the indeterministicism of measurement outcomes, and so on. Very basicly.

Of course, I know what it is, but I am extremely surprised to see that the majority of people are voting for it. Copenhagen, at least as it was formulated by Bohr, is a really rather radical view of the world that is not necessitated by the formalism of quantum mechanics per se. Nor is it accepted by the vast majority of physicists, at least not if you quiz them about its principles in any great detail.

There is some confusion between Copenhagen and "textbook" quantum mechanics. The latter really owes its origins to Dirac and von Neuman, and I can only suppose that this is what people are voting for.

 

[Stingray]

Why don't people worry about an "interpretation" of classical mechanics? People tie themselves up by talking about such an interpretation or another. Instead rely on the equations, they will only fail if QM as a theory is generally a false model.

Quantum mechanics has the measurement problem to worry about. There is no well-defined way to just "rely on the equations" in textbook quantum mechanics. You have to define an external classical observer, and say exactly what he is "measuring" for all times. It disturbs people that a supposedly fundamental theory seems to require the existence of a poorly defined entity that is external to it.

I agree that this is not usually a problem in practical applications, but the fact remains that we can imagine situations where the concept of a measurement device in the textbook sense does not exist (e.g. quantum cosmology). If it is fundamental, quantum mechanics should be applicable to all systems, and the various interpretations attempt to clarify these sorts of logical issues (at least the worthwhile ones do). Classical physics obviously does not have the same sort of vagueness about it, so interpretations aren't as necessary.

 

[masudr]

It disturbs people that a supposedly fundamental theory seems to require the existence of a poorly defined entity that is external to it.

It doesn't matter what disturbs people. It disturbed people that the Earth wasn't at the centre of the universe. So what?

If it is fundamental, quantum mechanics should be applicable to all systems, and the various interpretations attempt to clarify these sorts of logical issues (at least the worthwhile ones do). Classical physics obviously does not have the same sort of vagueness about it, so interpretations aren't as necessary.

Wavefunctions exist as superpositions until observed. Why is that hard to swallow? Two interacting systems exist as tensor products of the individual system until observed. Why is that so hard to swallow?

Classical mechanics does have the same sort of vagueness. For example, we immediately assume that the position of particles are represented by real numbers, and all motion can be described in terms of infinitesimals. These are not reasonable assumptions. In my opinion it is just as vague. If you mean QM is counter-intuitive, I would agree, but intuition means nothing in physics (although women's intuition is frightening sometimes).

 

[ashfaque]

As a mathematical physicist, I don't think interpretations matter. Schrodinger's equation will always exist as a fundamental concept of QM. So we can use it! And that's all that matters, in my opinion.

Richard Feynman said:


Now one may ask, "What is mathematics doing in a physics lecture?" We have several possible excuses: first, of course, mathematics is an important tool, but that would only excuse us for giving the formula in two minutes. On the other hand, in theoretical physics we discover that all our laws can be written in mathematical form; and that this has a certain simplicity and beauty about it. So, ultimately, in order to understand nature it may be necessary to have a deeper understanding of mathematical relationships. But the real reason is that the subject is enjoyable, and although we humans cut nature up in different ways, and we have different courses in different departments, such compartmentalization is really artificial, and we should take our intellectual pleasures where we find them.
----The Feynman Lectures on Physics


I would very much like to understand nature. That's why Interpretations matter to me.
Ashfaque

 

[Stingray]

Wavefunctions exist as superpositions until observed. Why is that hard to swallow? Two interacting systems exist as tensor products of the individual system until observed. Why is that so hard to swallow?

It's hard to swallow because it's not necessarily obvious when an observation takes place, or which quantity is being observed. In the end, you are of course trying to predict the values of certain observables, so your final experiment must be unambiguous. What happens at intermediate times though? You presumably start with a superposition and then what? Is it assumed that there can be no intermediate observations, and that one simply let's the wavefunctions of all the various systems -- microscopic and macroscopic -- interact through Schrodinger's equation (in principle)? I don't think this is mathematically equivalent to allowing multiple observations, but it should be.

I guess the issues come up when the observer is part of the system. The [measurement]->[wavefunction collapse] viewpoint should be equivalent to one which evolves the complete wavefunction of the observer+system, but that doesn't seem true.

I suppose I tend to worry about this because I have friends doing quantum gravity. I really have no idea how to unambiguously interpret models that quantize geometric quantities. It's quite a bit removed from what is taught in textbooks.

Classical mechanics does have the same sort of vagueness. For example, we immediately assume that the position of particles are represented by real numbers, and all motion can be described in terms of infinitesimals. These are not reasonable assumptions. In my opinion it is just as vague.

Good point, although I don't think vague is the right word to describe that. It is still straightforward to apply the formalism. Or am I missing something?

 

[masudr]

I would very much like to understand nature. That's why Interpretations matter to me.

This is all good and well, but we will never understand nature. If classical mechanics was true, we still would never understand nature. There are an infinite possible kinds of universe that could exist (whether or not we would exist in them is another matter).

Nature (or God or however you want to look at it) has made a certain choice, and selected certain (or perhaps only one) parameter(s) and that we will never understand.

That's why interpretations will never be complete. If Newtonian gravity were true, we could still ask, "Why should -g=a"? And we would never have an answer that could not be asked a similar question (don't say GR explains it, because it doesn't -- in fact GR assumes that Newtonian gravity is correct in the non-relativistic limit to determine certain constants; while GR provides a more fundamental understanding of gravity, it still does not explain everything -- e.g. Why does energy deform spacetime?).

 

[humanino]

see [thread=42975]another poll[/thread] in this forum...

 

[marlon]

i have chosen for many worlds...

marlon
runs and hides...

 

[metacristi]

As a mathematical physicist, I don't think interpretations matter. Schrodinger's equation will always exist as a fundamental concept of QM. So we can use it! And that's all that matters, in my opinion.

Why don't people worry about an "interpretation" of classical mechanics? People tie themselves up by talking about such an interpretation or another. Instead rely on the equations, they will only fail if QM as a theory is generally a false model.

In classical mechanics the interpretation belong to common sense.Though we might be not aware of that we do attach a proposed ontology to the mathematical formalism.In QM common sense interpretations do not exist thus we have,if we want to go till the end and complete the program,to attach a proposed ontology to the standard mathematical formalism of QM.Unfortunately there exist more ontologies compatible with observed facts,the most coherent with GR being,currently,the Copenhagen interpretation,in spite of its logical positivist nature (this does not amount to say that it has more empirical support than the other acceptable interpretations of QM).

Now it is equally valid rationally indeed to apply the principle 'shut up and calculate' and totally disregard the interpretation part (since anyway the novel [testable] predictions are made only by the mathematical formalism,the core of all existing interpretations).But I'm afraid this is too close to the positivist approach advocated once by Comte and Mach,not the best solution,as history of science proves plenty (since it does not really encourage creativity,the strive to complete one of the existing programmes).

 

[masudr]

In classical mechanics the interpretation belong to common sense.

There is nothing common-sensical about classical mechanics. The only reason it seems like it makes sense is because we have perceived a reality since birth that complies with the ideas set forth by classical mechanics.

Why should position of a particle be described by a continuous function of time? It is not obvious why it should. Why shouldn't particles jump in steps? The reason we feel classical mechanics makes sense is because ever since we started playing with bricks we've seen that we can move any object as little as we like. Assuming, for example, that the position of a particle is a continuous function of time seems reasonable, but appears to be incorrect. This is one of the many things that appear to make sense about classical mechanics.

I do not think that we should adhere to the "shut up and calculate" interpretation, because it does indeed help to have a feel for what's going on. In observer-less situations Copenhagen does indeed become blurry. Ultimately, it is personal preference until we can move further and show a link between some new formalism and a particular interpretation.

Finally, this has brought up an interesting issue. Does classical mechanics allow only one interpretation? I'll have to think about that one before I answer, so I thought I'd throw it open to the forum.

 

[CharlesP]

Failure

I find quantum mechanics to be a "failure" as a theory because it is impenetrable, counter intuitive and extremely difficult (if not impossible) to calculate. A friend once described it this way:
Someone makes what sounds like crazy statements and then to prove it he takes a few reasonable statements, turns these into equations and starts calculating. One wanders into a maze of equations and generally makes enough mistakes that the process ends right there. But occasionally the mathematical torment continues and you wander out of the woods not at all remembering how this whole thing got started. You look at the answer and it is indeed the crazy claim, but don't ask me to make sense of it.
I like the answers that I see here but I am far from getting the power and confidence that I feel classically. I consider interpretation to be extremely important because it is an agreed set of rules that enables performing the calculation algorithm correctly, and assigning numbers to physical properties.

 

[sifeddin]

ashfaque:
What about Shahriar Afshar's experiment and the Refuttal(?) of the Copenhagen Interpretation?

Yes what about him? give a link or explain

Stingray

Originally Posted by masudr
Why don't people worry about an "interpretation" of classical mechanics? People tie themselves up by talking about such an interpretation or another. Instead rely on the equations, they will only fail if QM as a theory is generally a false model.

Quantum mechanics has the measurement problem to worry about. There is no well-defined way to just "rely on the equations" in textbook quantum mechanics. You have to define an external classical observer, and say exactly what he is "measuring" for all times. It disturbs people that a supposedly fundamental theory seems to require the existence of a poorly defined entity that is external to it.

I agree that this is not usually a problem in practical applications, but the fact remains that we can imagine situations where the concept of a measurement device in the textbook sense does not exist (e.g. quantum cosmology). If it is fundamental, quantum mechanics should be applicable to all systems, and the various interpretations attempt to clarify these sorts of logical issues (at least the worthwhile ones do). Classical physics obviously does not have the same sort of vagueness about it, so interpretations aren't as necessary.

masudr:

Originally Posted by metacristi:
In classical mechanics the interpretation belong to common sense.

There is nothing common-sensical about classical mechanics. The only reason it seems like it makes sense is because we have perceived a reality since birth that complies with the ideas set forth by classical mechanics.

...

Finally, this has brought up an interesting issue. Does classical mechanics allow only one interpretation? I'll have to think about that one before I answer, so I thought I'd throw it open to the forum.

Here is a Newtonian Mach. interpretation for you

http://arxiv.org/abs/hep-th/0305017

By the way I vote for Bohm there are that new math language of Clifford Algebra that can give a non-intrinsic meaning to the uncertainty principle so why should not QM be deterministic esp. when the expectation value calculated for a "general state" (eigenstates composite) from the time dependent Schrodinger Eq. can have a non eigen value time evolution what a triumph for the state break principle