What do Philosophers think about the Many Worlds Interpretation of quantum mechanics?

Question

One of the interpretations of quantum mechanics is the Many Worlds Interpretation which basically states that the universe as a whole develops like an unobserved quantum system, and any observation effects ("collapse of the wave function") are illusions which are caused by the observer getting entangled with the observed system, which effectively causes a split of his world into many worlds, one for each measurement outcome.

Most physicists are against this theory because those other worlds are, by definition, unobservable, and thus violate the common positivist view. However I'd be interested in what philosophers (especially non-positivist ones) think about that interpretation. Is it philosophically sound, or does it have fundamental problems?

Answer 1

The intersection of metaphysics and quantum physics is the best place to be! There are so many interesting questions about the nature of reality that are posed in modern quantum physics. Just as you've stubbled on, one of this problems of philosophy of physics is the Many Worlds Interpretation.

My sense (I'm an undergrad, so take this for what you will) is that your general scientific realists and determinists (not mutually exclusive) will not be in favor of the Many Worlds Interpretation. I say this for two reasons: (1) quantum logic is a very new field and (2) the interpretation itself has some interesting metaphysical consequences.

To elaborate on the second point, to assume that the interpretation is true and that an infinite number of possible worlds are generated by each individual decisions that individuals make (ignoring the more complex problem of event occurrences and just focusing on choice). To allow for an interpretation that presents within itself a plurality of possibilities for the next 10 seconds, let alone the next 10 years, increases the importance of any individual choice. My decision to wear jeans instead of khakis may be a decision that is required to lead to World War III happening in 2050 rather than in 3000. Still you run into ex post facto bias.

This probably isn't the greatest explanation (as it lacks all specificity to appeal to a more general audience), but its just one undergrad's opinion :)

Answer 2

Questions of the form 'What do philosophers think about x?', where x is a broad topic, are doubly difficult to answer comprehensively, because there are so many interpretations of x and so many philosophical opinions on each interpretation. Given that, I will confine my answer to some observations I find interesting and hope that you will too.

The original formulation of quantum mechanics, known loosely now as the Copenhagen interpretation, associated mathematical functions- called wave functions- with particles and systems of particles, and assumed that under certain circumstances wave functions would change instantly when a 'measurement' was performed on the particle or system associated with the wave function. This presented two obvious objections that are still not resolved to everybody's satisfaction today, namely:

How and why can the assumed change happen instantly everywhere?

More importantly, what makes a 'measurement' special, given that it is presumably just an interaction between the quantum particle being measures and whatever collection of particles forms the measuring device?

There have been many different approaches to resolving these objections, one of which has evolved into a range of ideas now known as MWI. I say a range of ideas because there isn't an authoritative single definition of MWI, and some of its incarnations are far more plausible than others (IMHO). The 'pop science' idea of there being literally multiple Universes each as real as the one you suppose you are in is a classic example of an extraordinary claim utterly lacking in extraordinary evidence, and I follow Hitchins' maxim in relation to it- what can be claimed without evidence can be dismissed without evidence.

Answer 3

According to the PBR theorem, since the quantum wavefunction has been directly measured as a real physical object, the vision of the universe no longer can be considered psi-epimestic (merely information contained in the quantum wavefunction). The possible remained alternatives are psi-ontics (real objects outside our conciousness) or psi-ontic-epistemics (information with an objective underlying reality) Thus, the Copenhagen interpretation was shifted in favour of the Many Worlds Interpretation (MWI). In MWI you can imagine yourself living in infinite copies of yourself, one for each possible universe, with infinite outcomes. Therefore, if in this universe you are the Dalai Lama, then in another universe you are Adolf Hitler. In my humble opinion, that's one more reason to believe that quantum mechanics theory should not be extended to our common macro reality and our human beliefs, otherwise we risk to fall into an absolute relativism and our life could stick to just a random nonsense. That's why I blame quantum mysticism or, in general, theories which want to merge science and religion. Nevertheless, science is falsifiable, as stated by Karl Popper. Thus, even quantum religions should be forced to review their statements, and that is a nonsense too. That's why I do not trust too much New Age an other quantum woo beliefs.