Quantum Mechanics – Why is the Copenhagen Interpretation of Quantum Physics Widely Accepted?

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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?

Best Answer

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.

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