Which interpretation of Quantum Mechanics is more correct?

[I_Pwn_Crackpots]

In your opinion, which of the various interpretations for quantum mechanics out there do you think is the correct stance? For those of you who don't know, there are many interpretations of the theory, due to the fact that nobody can make much sense out of the experimental outcomes. As it is completely different from everyday perspective and defies all common sense, various groups of people interpret the theory differently. But anyways, here are some of the best known ones:

 

1. The Copenhagen Interpretation

2. Many Worlds

3. Anthropic Principle

 

 

 

I personally take the Copenhagen Interpretation as the best one, and indeed it is the standard view of today's scientists. In a nutshell, the Copenhagen Interpretation basically says that quantum theory doesn't really describe any kind of reality in the usual sense, it only predicts the outcomes of an experiment within a given probability of success and at best displays the knowledge the experimenter has about the parameters of a given experiment. Basically, the theory works, the equations are accurate, and that's all we really need to concern ourselves with.

 

The Many Worlds Interpretation holds that all the things that could happen actually do. That is, yes, Schrodinger's cat can be both dead and alive. All that happens is that alternative universes branch off at each of the possibilities, in that in one you have a dead cat, and in the other you have a live cat. Of all the ones listed, this is the one most popular and has it's followers in the realm of science fiction, where you have multiple universes. Personally I think that this interpretation is seriously flawed, and IIRC I think it has been debunked a while ago.

 

The Anthropic Principle holds that all of the wave functions, superposition, etc, etc exist, and collapse only when an observer is present. That is, Schrodinger's Cat is both dead and alive until you observe it, and that is when the wave function collapses. This principle is also used in various interpretations of cosmology as well. Personally, I think the Anthropic Principle is complete garbage.

 

 

But, of course, if you think that any of the other interpretations are more valid, I would like to see your reasoning. So, which of them do you think is the best one?

[Royston]

I wrote a short essay on the Copenhagen Interpretation about a month back, I'm no QM expert, but the only issue I have is the boundary between the classical system (i.e the measuring device or more specifically the measurement itself) and the quantum system (that is what is being measured.) It just seems incomplete to me...or not satisfactory to leave it at that.

 

I read about consistent histories shortly afterwards, which does away with the classical measuring device, and treats it all as a quantum system including the act of measurement i.e probabilites rule...there's more to it than that, so I'll look for a link. However, after making my vote, I decided to read back on consistent histories, and surely it's impossible to get exact solutions ? In any case, I think I should have read more on the subject before casting my vote, but on face value consistent histories does deal with the boundary problem.

 

If I have this wrong, or I've <ahem> misinterpreted the consistent histories approach, please correct any of the above.

[Marbleman]

There is another interpretation - "Smooth Quantum Mechanics", at

http://philsci-archive.pitt.edu/archive/00004199/

In this paper, it is showed that we can construct a quantum mechanics without wave function collapse, such that:

- the Schrodinger equation is valid all time (there is no violation of the unitary evolution)

- what appears to be wave function collapse can be obtained without discontinuities and unitary evolution violations, by the means of "delayed initial conditions". Some examples (two-slit, Mach-Zehnder, EPR, delayed choice experiments) show that this is indeed the case.

 

The QM simply becomes a unitary evolution described by Schrodinger’s equation, and the measurements serve as establishing initial conditions. These conditions are established with a delay. Not all the parameters identifying the precise solution of the Schrodinger equation are fixed from the “beginning of times”, but they are fixed later by measurements.

 

For the ones that consider the collapse irreducible to unitary evolution, it is presented "A Direct Interpretation of Quantum Mechanics", at

http://philsci-archive.pitt.edu/archive/00004194/

which can help also as an introduction to QM, and a preliminary to the SQM article.

 

I'll vote for the "Smooth Quantum Mechanics", of course

[ajb]

Can any interpretation be correct?

 

After all an interpretation is an attempt to describe mathematical structures and calculations.

[Martin]

Can any interpretation be correct?

 

After all an interpretation is an attempt to describe mathematical structures and calculations.

 

That's a good question to be asking! I think some interpretations can be better than others in the sense of being more fruitful---more apt to lead to new understanding, new mathematical development.

 

The mathematical model, by which one calculates and predicts, is what describes nature and can be more or less correct. By contrast, the verbal interpretation is not describing nature but is helping one's mind adapt and assimilate to the mathematical model. A good verbal interpretation is one that puts one in firm intuitive contact with the model and enables one to grow new ideas.

 

So we are guessing which will be the most helpful and fertile interpretation, going forward. It is in that spirit that I answered the poll.

I have the impression that I've already seen progress in Quantum Cosmology stemming from the Relational QM (RQM) interpretation. It helps address the question of what is time? And it helps take care of the problem of quantum cosmology that since the universe includes all existence there is no outside classical observer as there is in the Copenhagen setup. In other words, RQM is more complete---it can handle situations that ordinary Copenhagen cannot. This is merely my impression based on casual observation---haven't studied foundations enough to make definite statements.

 

A accessible paper on RQM is the 2006 paper by Rovelli and Smerlak

http://arxiv.org/abs/quant-ph/0604064

The paper aims to show how in RQM one resolves or avoids some of the puzzles, like the EPR one, that can be a nuisance in some other interpretations. Collapse of the wavefunction is understood without resorting to a fantasy of branching multiple universes. So it is nice simple and convenient, but it is merely an interpretation and the real test is (as your comment suggests) does it lead to conceptual progress?

 

Ajb, I hope you were able to take part in the Sussex workshop as planned! How did it go? Any talks particularly helpful?

Edited November 1, 2008 by Martin

[ajb]

Hi Martin,

 

the school was very useful, I now have some (very limited) knowledge of renormalisation group flows. More than anything I have made some professional contacts and I am now attending the Sussex seminars. I am giving an informal seminar in a few weeks time. I will talk about supermanifolds and their neighbours. (maybe a topic for a future thread.)

 

As for this poll, like you I can only think of the "correct" interpretation as being the most useful one. But again, that is a very vague definition and will depend on personal choice to some degree. I agree that it should be the one that leads to "further work".

[Tom Vose]

And thus the pain persists! Quantum theory is a very successful theory, if nor the most successful theory of all time… But we struggle to bring together a unified theory, and we also struggle with our interpretations. Some scientists don’t worry about the interpretation of physics… Other’s find the interpretation pivotal to our understanding of Quantum Physics.

The problem with quantum theory isn't just that it is incomplete, but that there are also countless problems - and here we shall quickly summarize a few of them through their vague interpretations...

 

The Copenhagen Interpretation:

Developed in 1920's by the 'father and mother' of physics called Niels Bohr. He named his work after his own town, in Denmark. This interpretation on fundamental behaviour became 'textbook' knowledge, and became the most accepted quantum interpretation ever devised. Though, despite this fact, as you may know, many have long abandoned this interpretation. With all of reality due to a collapse postulate, the observer and the observed play intrinsic roles. However, this world is shadowed by ignorism, and that the interpretation states that not everything can ever be known... that is, if it something isn't measurable or experimental, why bother contemplating such a fact?

Another problem was the infinitesimal world of fundamental coherency. Somehow - just somehow... particles merge together and create entire systems, despite being made up of quantum wave functions. The question is, without any particular collapse on the fundamental level, how do these statistics create whole entire systems? How does reality make sense, of what should be totally senseless? This paradox is most associated with the Schrödinger cat experiment. The Copenhagen interpretation is [vague] about this ''leap'' from the fundamental to the everyday objects we envision and perceive. For instance, it states that ''everyday objects are far too big to show any weird behaviour.''

Howsoever, this isn't enough for certain scientists, and it isn't really difficult to understand why. More was needed in physics... new science was just around the quantum corner...

 

The De Broglie-Bohm Interpretation:

First proposed by the 'quantum pioneer', Louis de Broglie, who believed that all quantum interaction and weirdness was all put down to ''pilot waves''. His idea was put down into theoretical development by the American physicist, David Bohm, who inexorably seeked for the clarity in the obvious vagueness of the standard interpretation by using 'hard law physics'. A quantum system is run by definite properties, even when not being observed, by virtue of a 'pilot wave' accompanying every particle.

However, all of this comes with the so-called, ''quantum potential;'' this is an all-spacetime filling field that is supposed to inform particles about their environment. It is this supposed field that ''tells'' particles how to behave when a certain apparatus is used to observe them... More importantly, the quantum potential is able to do all this at superluminal speeds. It was this that really brought the theory to a halt in the 1950's... however, it became revived in the 80's when the ''Aspect Experiment,'' which proved entanglement, had shown such instantaneous effects to be intrinsic within any good quantum theory.

 

The Existential Interpretation:

In the 1980's, a growing number of smartly-minded scientists and theoretical astrophysicists began to study the interactional coherency between quantum systems and their surrounding in a more investigated research.

The Existential Interpretation worked with, what is called, 'quantum decoherence,' which showed that fundamental laws are inconsistent when compared with everyday macroscopic quantum systems. In the 1990's, Wojciech Zurek of the Los Alamos National Laboratory, New Mexico, believes wholeheartedly that quantum decoherence does not cause the ''collapse'' of all but one of the possible conditions of a quantum system, but just affects some quantum states more than others. It is inexorably the value of things we observe everyday.

Dr. Zureks interpretation involves the Copenhagen interpretation - but eradicates the theory of the so-called 'collapse', and instead opts for the multiverse interpretation. However, as you might know, the Existential Model states the existence of 'decoherence,' which is a bona-fide fact of physics, as it is known to exist. So far, this interpretation cannot be disproved.

 

The Alternate Universe Interpretation

Also known as 'Multiverse Theory,' 'Many worlds Theory,' or 'Parallel Universe Theory'. Created by Hugh Everett the III, it was a way of explaining the estranged wavelike and particlelike properties by a constant merging and splitting off of universes. These universes come into existence due to the wave function, and no collapse occurs in this interpretation. Instead, the wave function represents our universe, splitting off into as many possibilities the wave function ascribes. The problem with this theory is that we have never observed another universe. Also, the theory itself is problematic, as it has a high improbability as being the correct interpretation that fits nature. This is because the idea of the constant splitting and merging brings out that little voice in the back of your head saying, 'something just isn't right.'

The idea of the universe, 'playing it safe,' like this, could explain why uncertainty appears in our reality - because every possible outcome is shared among every universe, paradoxically sharing the same space.

 

The point of all this? Well, it seems that the Copenhagen Interpretation is the most accepted. When you ask what interpretation is more right, you end up explaining it as, ''they are all right.''

[ajb]

Some scientists don’t worry about the interpretation of physics…

 

I would say that I belong to this group. Interpretation and more generally philosophy can be useful, but it is no substitute for "real" physics.

 

When you ask what interpretation is more right, you end up explaining it as, ''they are all right.''

 

Indeed, my point was that it is not obvious what you mean by "correct/right" or indeed if that is even a sensible question.

[Tom Vose]

Yes i don't worry about any standard interpretation however, but if i had to choose, it would be the Copenhagen Interpretation.

[kleinwolf]

What is incomplete measurement ?

 

-) meaning that QM measurement are in fact not pushed to whole precision

-) measuring only one subsystem of a multipartite system ?