I didn't intend for this post to be so long, but I couldn't find a short way of saying it. This is why I've been trying to stay out of discussions about interpretations lately. They take too much time.
ThisIsMyName said:
Sure it can't be "debunked" as ghosts can't be debunked, because you can always move the goal post "nono but the ghosts are invisible so by definition you can't prove them, but they DO exist".
It's that kind of pathetic logic.
I agree about the ghosts, but I don't think it's an appropriate analogy.
ThisIsMyName said:
Also let's not forget that Tegmark is the multiverse mania guy, he doesn't just believe in other universes out of some rational conclusion, he WANTS there to be other universes, he has like 4 different levels of multiverses without any proof.
So obviously he'll dismiss any criticism out of emotional response, not logic or rational thinking.
I think the stuff he wrote about parallel universe is really good, and certainly not a reason to expect him to be irrational.
ThisIsMyName said:
What interpretation do you adhere to?
I need to say a few things about "interpretations" in general before I answer that.
The way I see it, a theory is defined by a set of axioms that tells us how to interpret some piece of mathematics as predictions about results of experiments. So a theory already includes one kind of "interpretation". An
interpretation of a theory of physics must be something very different, because the theory already includes an interpretation of the first kind. The only thing it can be that makes any sense to me, is an answer to the question "What is the theory telling us about what actually happens to the physical system that the theory is making predictions about?
In other words, an interpretation of the first kind turns a piece of mathematics into a theory, and an interpretation of the second kind is either a claim that the theory doesn't describe reality, or an attempt to turn the theory into a "description of what actually happens". Note that all theories before QM had an
obvious interpretation. There was never any debate about what the theory says is actually happening. For example, Newton's theory of gravity makes predictions about what results you will get if you measure the position of the Moon, and everyone agrees that those predictions describe (approximately) what's actually happening to the system even if no measurement is made. The Moon is there even when nobody looks.
Since I consider QM to be a theory of physics, and since I consider a theory to be defined by its axioms, I have to choose some specific list of axioms to define what I mean by "QM". I choose the standard axioms about Hilbert space and the Born rule, not because I think they must be the best, but because that's the set of axioms that most people are familiar with (and the ones I'm the most familiar with).
Now that I have defined what I mean by an interpretation of a theory of physics, and what I mean by QM, I'm finally ready to start talking about interpretations of QM. The way I see it, there are only two! Either QM describes reality or it doesn't. The claim that it doesn't is what people call the "ensemble interpretation" these days. The claim that it does is what I would take as the definition of a new many-worlds interpretation. (I don't consider Everett's MWI an interpretation of QM. It's nothing more than a failed attempt to find a different way to turn the underlying mathematics into a theory of physics. It was never intended to be what
I would consider an interpretation of a theory).
It's funny that if you ask the most aggressive MWI-haters which of these two options they prefer, they usually say that the first option (QM describes reality...which I take as the definition of a MWI) is obviously true and that the second one (QM doesn't describe reality) is crazy nonsense. They dismiss the second one because it suggests that reality either isn't described by mathematics, or that there's a more fundamental theory than QM in which the variables are "unobservables" or observables with weird properties (e.g. non-local or contextual observables). They don't even want to think about the possibility of a "weird" fundamental theory as long as there are no experiments that contradict the predictions of QM. And most of them think it's self-evidently true that a theory that makes good predictions about reality must also be a good
description of reality.
So which interpretation of QM do I prefer? I actually don't have a clue which one of the two I should think is more plausible. Two years ago, I would have said that I definitely prefer the ensemble interpretation. Now that I understand that there is a MWI that isn't fundamentally flawed like Everett's MWI, I'm torn between the two options. One thing that could tip the balance toward this MWI is if it turns out to have a wider range of applicability than the ensemble interpretation. For example, if it's neutral about whether entropy is increasing or decreasing with time, but identifies the branches where entropy is increasing with the branches that
can contain conscious observers, we might have an anthropic argument that solves (or rather eliminates) the mystery of why the universe started out in a low-entropy state. For the moment, I'm leaning towards thinking that such arguments can be made.
I don't understand any of the other "interpretations" as well as these two (so I could be wrong about what I'm saying here), but it seems to me that most of them are just loosely stated ideas about what reality is really like. Such speculations are of no interest to me, and I don't think they should be called "interpretations". A few others seems reasonably well-defined at least, e.g. de Broglie-Bohm, transactional and consistent histories, but have the first two even successfully replicated all the predictions of QM? I'd be surprised if the answer is yes. (Doesn't dBB have problems with SR, and isn't transactional specifically for electromagnetic interactions?) And the last one just looks like a many-worlds interpretation of a slightly different but equivalent theory. (I consider two theories to be different if their axioms are different, and equivalent if they make the same predictions).
ThisIsMyName said:
Also, even if you take the wavefunction to be physically real and represent everything you doesn't inevitably end up with a many worlds picture, you can just as easily end up with a single world picture which select a random world in accordance with Born's rule, as Adrian Kent suggested as a toy model.
I disagree. I think that requires an additional axiom, which says explicitly that exactly one of the "worlds" is real. I don't mean that this makes that idea wrong, but it means that this single-world interpretation isn't an interpretation of QM, but an interpretation of the theory defined by the axioms of QM
and this additional axiom that has no effect on the predictions.