Why is the Copenhagen interpretation of quantum physics the most widely accepted one?

Question

I've been digging a lot into quantum physics in the last few weeks. I didn't care much about the maths, just about what empirically happens to get a conceptual idea about quantum phenomena.

The most widely accepted interpretation of quantum mechanics seems to be the Copenhagen one. If I got it right, it's heavily relaying on the two following principles (among others):

• Superposition: a quantum system is at the same time in all the states it could possibly be in. When it's measured, it instantaneously collapses in a single state.
• Entanglement (aka "spooky action at a distance"): if two or more quantum systems are entangled, it means that some of their properties are correlated. When measuring a system, all the entangled ones collapse in a state coherent to the measured one. Simultaneously. No matter how far away they are to each other.

I'm not able to believe it. It allows some unrealistic paradoxes (e.g. Schrödinger's cat paradox), and I have the feeling that this interpretation (and its consequences) is what makes quantum mechanics look so weird, mysterious, unnatural and spooky to the public. Besides I've read from a few sources (like this Google Tech Talk) that this interpretation has proven to be broken: the math says everything is continuous and doesn't hint to anything like collapsing, and even more important, the quantum eraser experiment contradicts the Copenhagen interpretation.

The second most popular interpretation, many-worlds sounds a lot more natural to me, although it strongly smells like science fiction.

I believe there must be many interpretations that would hold better and would be a lot less weird than the two mentioned ones.

What I'm wondering is, then: why does the Copenhagen interpretation (and to a lesser degree the many-worlds one) remain the most accredited one?

Answer 1

Why is the Copenhagen interpretation the most accepted one? I would say the answer is this:

• it's the oldest more or less "complete" interpretation
• hence you'll find it in many (all?) early text books, which is basically from where people writing modern text books copy from.
• the overwhelming majority of physicists doesn't really care about the interpretation, since it (up to now) is only a matter of philosophy. We cannot know what interpretation is correct, because we can't measure differences, hence the interpretation question is a matter of taste rather than scientific knowledge.
• most standard QM courses at university (at least the ones I know) don't bother with the interpretation. They just introduce the concepts, updates of knowledge, etc. and in that sense, the Copenhagen interpretation is just convenient.

This implies that if you ask a lot of physicists, some have never even thought about the matter. If interpretation is a matter of philosophy, why should we worry about it then? I can think of two points here:

a) By thinking also about interpretations of our theory we may come up with new theories that give us "nicer" interpretations of existing results, but they are essentially inequivalent to quantum mechanics. Bohmian mechanics from what little I understand about it is such a candidate, which might turn out to at one point make different predictions than classical quantum mechanics (up till now, it's just a different interpretation). This is of course a very good reason to think about it, because if quantum mechanics can not explain everything and there is a better theory, which can explain more with similarly "simple" assumptions, we want to have it.

b) It might help our understanding of "reality". This is only interesting, if you believe that your theory describes reality. If you believe that we only ever create effective models that are limited to a certain domain of our variables, then interpretations become uninteresting. Your model isn't the real deal after all, so why bother with something, you can't measure? It doesn't enhance our knowledge.

So, if you don't believe that science should (or even can) provide ontologic theories and if you don't think a better theory than quantum mechanics is maybe just beyond the horizon, then you don't care about interpretations of quantum mechanics. Otherwise, you should.

Answer 2

Due to historical reasons, physicists who do not have a strong preference for a particular interpretation default to the Copenhagen one, despite some of its pseudo-mythical outgrowth - which you can just ignore if you are in the 'shut up and calculate' camp.

It doesn't help that every other interpretation (at least those I know of) contains some flaw or quirk I find unacceptable as well, which would leave me with the statistical one (and perhaps consistent histories), basically not explaining anything at all.

The ones I like best are Cramer's transactional one and de Broglie's double solution, with the caveat that these should be backed by a theoretical framework beyond quantum mechanics, but aren't.

Personally, I'm one of these cranks who think that we should be able to back quantum mechanics with a realist theory (but a superdeterministic one): Start from de Broglie's double solution, throw in the geon model of elementary particles and ER=EPR and you're good to go.

Answer 3

I believe that Bohr's strong personality is the major reason for the popularity of the Copenhagen interpretation, and I agree that "Shut up and calculate!" is the default interpretation for those not concerned with ontology.

Re superposition: all it says is that if there are two possible states then their linear superposition is also a possible state. A system is in only one state, but you can express that state as a linear combination of other states. Think of them as coordinates.

Entanglement is a consequence. not a basic principle. See, e.g., https://en.wikipedia.org/wiki/EPR_paradox.

Answer 4

Fundamental flaws in basic reasoning and perpetuation of myth (largely perpetuated by pop culture physicists granting both fame and money). In science, the best interpretation is the one that looks at the physical truth and doesn’t make a grand over reaching proposition counterintuitive and against all reason.

So that if I see the two slits experiment, I notice that when a light passes through these two slits, I can observe an interference pattern, the only conclusion is that given the exact same slits, with the exact same light passing through, we should observe the exact same interference pattern.

If I then pass this light through a crystal, and get two independent beams with complimentary properties, all I can really say is that given the same crystal and the same light, I should see two independent beams with complimentary properties.

Additionally, just because a mathematical model works doesn’t mean it is a representation of the physical universe in any way. There are numerous valid mathematical means to show the revolution of the sun around the earth…. This is inventive, but not very useful to the physical reality of our solar system.

We can only conclude from a working mathematical model that we have discovered a mathematical model that works. (It’s a huge leap to say that our model defines reality!). For instance, I might build an accurate model of a town using glue and carved figures, but that in no way should ever mean that real towns are built using glue and carved figures.

Finally, any physicist that tries to tell you that there is no difference between saying “we cannot simultaneously observe a particles position and its momentum” and “photons do not have both position and momentum” is missing a critical point. Just because we cannot with our instruments observe a photons position and its momentum does not imply, suggest, or in any way indicate that photons do not have both a position and a momentum. And, btw…. We can… just simply catch a photon (quanta of light) inside a polarizing lens (your sunglasses)- and wow, we have a location- the spot the photon last touched, and a momentum- whatever the particular frequency was that was absorbed!

Einstein’s main criticism about QM then (and most reasonable people’s criticism now) was/is that quantum mechanics has great math but lousy physical interpretations. He also said that the nature of physics demanded that we look deeper than just a probability. That we needed to investigate something real, measure something real. That physics is about the real physical world. And that QM just completely forgets /loses sight of the physical world (admittedly not good for physics). http://arxiv.org/pdf/1107.3701.pdf

Answer 5

Copenhagen is considered the de-facto interpretation of Quantum Mechanics for historical and sound practical reasons. It is the least speculative of the various interpretations (no need for a multitude of alternative Universes or interactions with consciousness or ...) and the product of much debate amongst the great minds of the time (Bohr, Heisenberg, ...)

The Google Tech Talk is very confused. I suggest that you ignore it.