Since I’ve never been polled I thought I’d add my voice to those who find the MWI to be nonsense as a solution to the measurement problem. In fact I have a similar feeling about the decoherence approach too. In looking through the comments here I don’t find a counterargument to the point that nothing ever actually happens in the MWI, so what could the probabilities be refering to? I don’t see any real response to the question of how the different possibilities interfere with each other, if they are in different universes, either.

I think the attraction of the MWI is something like this: measurement in quantum mechanics is so obscure, and has these pesky associations with consciousness (and therefore with mysticism etc), that many scientistic-minded people want to get as far away from these things as possible. The conceptually cleanest way to solve this (psychological discomfort) seems to be to deny troublesome phenomenon.

It reminds me of how, in an attempt to be “scientific” (not to say positivistic), certain philosophers and scientists will deny the existence of consciousness itself because it does not (so far) have a place in our physical theories.

Am I the first in this thread to mention that we are not forced to choose between the Copenhagen Interpretaion and the MWI? The natural alternatives are “objective collapse” theories. With those we can have genuine ontological measurement events that actualize particular definite outcomes, so that the probabilities in our theory actually refer to something. And, we can avoid the frightening apparent dependence on human observers that might have led us to run to the MWI, because the state-vector reduction is induced by some objective mechanism or criterion (e.g. a coherent mass threshold, or something).

I don’t understand why this interpretation is not the default. Maybe to some it seems to flirt with panpsychism? Maybe because it would appear to violate Lorentz invariance (but no more so than non-local EPR correlations)?

No, but maybe one day.

“If so, since “events are the primitive objects” and have no temporal duration, how do you use events to construct trans-temporal objects?”

Good question – one would definitely need a way of constructing things like world-lines. On the other hand, I didn’t say that events should the only objects in the theory, just the primitive ones.

“True, all I meant is that it is pretty easy to imagine formulating a vast array of different theories in which events are the primitive objects with all sorts of different geometries. I’m not talking about different solutions to GR per se, but rather situating GR within a framework of possible theories, all of which share the feature that spacetime is not a fixed, flat background structure. It may not be easy to actually find interesting solutions to any of these theories, but that’s beside the point because we are not talking about the practicalities.”

Are you working on such a theory? If so, since “events are the primitive objects” and have no temporal duration, how do you use events to construct trans-temporal objects?

The problem with such a theory is not that it isn’t consistent with experience, but that it is not scientific. It undermines a fundamental assumption that we have to make in order for scientific reasoning to go through, i.e. the assumption that the universe exists and we obtain reliable data about it through observation.

It seems to me if a giant green goblin exists, then the universe exists. The notion of a hidden substrate on which our perceived universe hangs doesn’t strike me as particularly non-scientific. There is a plausible argument to be made that the quantum world is just such an example of that. In other words, the universe we perceive doesn’t exist, but instead a weird quantum universe of particles that only physicists can detect, which work in such a fashion and with such rules that we perceive the “normal” universe of macro phenomena. Of course, quantum theory does have all sorts of experimental corroboration, even though very little accessible to most people, and is falsifiable, and the giant, green goblin is not. On those grounds, I would say the green, goblin theory isn’t scientific.

It seems to me a lot of philosophizing around this issue is an attempt to make our knowledge seem more than it is. More certain. More universal. More relevant to whatever is the basis of reality. All science needs is that our observations are reliable enough to generate generally useful theories. Where there are holes, we try to do more science. Sometimes that succeeds, though in modern times, it has produced some theories like quantum mechanics that put a strain on philosophers. So far, no one (at least publicly) has discovered any rabbit hole whose other side makes the entire rest of physics seem the contrivance of another intelligence, whether green goblins or Leibnizean gods . Consider, though, that in the various science fiction stories that use that plot device, it does not make science impossible. It merely means there is an apparent physics, and a physics behind that that we haven’t yet discovered. And there might be one behind that. Surely one of the lessons of science and philosophy is that we can never know the ground of being, the bottom-most substrate, the ur-reality that is not itself produced by something more basic. If that is what you mean by science, and what is required to make science possible, then you’re right: science isn’t possible. We’re not just watching shadows on walls, but don’t even know whether the things casting those shadows are at the bottom, or are themselves shadows. That doesn’t make it impossible to learn some of the rules of the wall we see.

The problem with such a theory is not that it isn’t consistent with experience, but that it is not scientific. It undermines a fundamental assumption that we have to make in order for scientific reasoning to go through, i.e. the assumption that the universe exists and we obtain reliable data about it through observation.

My argument is not that MWI is inconsistent with experience – people have put a lot of effort into explaining how it can be made so and I think think that they have developed a pretty good story at this stage. The question is simply whether it undermines an assumption that is basic to the scientific method, and is therefore not a valid scientific hypothesis. Now, admittedly the case of MWI is much closer to the borderline than the green goblin theory, but I still think that having objective data, i.e. definite outcomes of experiments, is a pretty basic assumption behind the scientific method. Quantum theory is obviously consistent with this assumption, since there are other consistent interpretations that assert it, so I don’t see why so many people feel compelled to give up such a basic assumption by adopting MWI.

Now, is there a Quinian argument to be made against the many-worlds interpretation? I think so. The idea is that when we apply the scientific method we assume we can do experiments which have actual definite outcomes. These are the basic data from which we build a confirmation or refutation our theories. Many-worlds says that this assumption is wrong, there are no fundamental definite outcomes – it just appears that way to us because we are all entangled up in the wavefunction of the universe.

The problem with this argument is that the MWI models exactly the kind of world we do in fact experience, and as far as we know, is perfectly consistent with the evolution of animals such as we are, who are capable of formulating theories such as it. I don’t see how the restriction that physical theories have to support a universe where the development of physics is possible is a whit stronger than the restriction that physical theories have to fit physical observations. At least, not without some proof or demonstration that the mind requires physics above and beyond what is necessary for atoms, stars, and quarks.

I think you’ve blurred the synthetic/analytic distinction and the a priori/a posteriori (that’s the word you were looking for) distinction. The former is about meanings, and the latter is about how we learn things or could imagine them to be. So the synthetic a priori is supposed to be the stuff that isn’t true just in virtue of meaning, but is still so fundamental that we couldn’t imagine it being any other way.

And actually, Quine’s major point is that the synthetic/analytic distinction doesn’t really make any sense. His view seems much closer to what you describe as a revision of him, than to your original description. He doesn’t think there are some foundational truths – the picture he gives in “Two Dogmas of Empiricism” is the “web of belief”. Some things are more central than others, but anything could in principle be challenged. So some sort of graph with a power-law distribution of vertex degrees would be an appropriate model.

Anyway, I consider myself generally Quinean about metaphysics, and that inclines me towards the MWI. As others have pointed out, Copenhagen is just really weird. Admittedly, I don’t know enough about the Bohm “pilot wave” interpretation to have any idea how it compares. And of course, people have given broadly Quinean or Occamite arguments for just about all of the different interpretations – which is why there are still so many candidates.