I’ve written before about the problem of having in-between views on controversial subjects in blogdom. This is something that also comes up in Jessica’s excellent entry on online culture, and has been scientifically demonstrated in political contexts.
I’m somewhat bemused, then, to see the same thing happen in a physics context. A while back, I got an email asking about quantum foundations that read in part:
I’m very keen to understand why you and Andrew Thomas reject [the Many-Worlds Interpretation of QM].
I’d be very happy if you’d take a few minutes to try to describe why you think MWI is wrong and also what you think is more likely to be true and why.
(I added the link, for context.)
This is kind of amusing to me, as I have previously taken some flak here for being excessively pro-MWI, in the view of some readers. I just can’t win.
My real view is, alas, kind of wishy-washy: I’m agnostic about quantum interpretations, mostly because as far as we know, they’re all meta-theories, not proper scientific theories. There is no experimental test known that clearly favors one interpretation over another, so which one you like is ultimately a question of taste. They’re kind of fun to talk about, but absent a way to distinguish between them, they’re not more than that.
Another way of saying that would be to say that I subscribe to the “Shur Up and Calculate” interpretation (a phrase that apparently originates with David Mermin in a 1989 column in Physics Today, so please don’t attribute it to Feynman). The concrete predictions of quantum physics are tested to something like 14 decimal places, and the choice of interpretation doesn’t affect any of those results, so just focus on what works, and leave the meta-theorizing to philosophers.
The clearest statement I have about what Many-Worlds is really about is this old post on MWI and decoherence, which can be found in a much cuter canine version in How to Teach Physics to Your Dog (available wherever books are sold, hint hint). That said, here are a few general things I will say about it:
- If you think about what the MWI actually says, particularly in the modern versions involving decoherence, it’s pretty elegant and not at all unreasonable. A lot of the arguments against it are based on confused misreadings of what it’s about, and end up constructing elaborate refutations of things that are not actually part of the theory.
- Sadly, a lot of the pro-MWI stuff out there is also pretty bad, putting forth some pretty outlandish claims, or offering hand-waving explanations of the theory that make it more confusing than it needs to be. Some of this material is taken way more seriously than it ought to be, in my opinion.
- In the end, the modern interpretation boils down to having a wavefunction with multiple components that are prevented from influencing one another through random and unmeasured interactions with a fluctuating environment. These are not parallel universes in the Star Trek sense, with entirely separate near-duplicate copies of every material object, but rather superpositions of states of a single set of material objects. Far too much is made of the “parallel universe” angle.
- Most of the objections to the theory are fundamentally just aesthetic objections– all those extra wavefunction components seem like an awful lot of overhead to be carrying around; other people object to the fact that the theory contains branches describing really improbable events. The people making these arguments get very worked up about them, but I don’t find them particularly convincing.
- The most serious real problem for the theory has to do with figuring out the origins of the measurement probabilities observed by people within the theory (that is, given that all possible outcomes occur somewhere, why do we see some events occurring with higher probability than others). I’m not entirely sure I understand this objection, either, but it’s regarded as important by many people who have thought deeply about this.
- Nothing you can do will allow you to shift your perception from one branch of the wavefunction to another, no matter how much you want to be in a more favorable universe, or how much time you spend meditating, or what drugs you take. Nothing. Anybody who claims otherwise is a charlatan and a crank and should not under any circumstances be given any money.
I’ll also say that my opinion of the MWI improved dramatically when I started reading more about it in order to write the book, so I would recommend that to anyone who is interested in the subject. Sadly, though, most of the popular treatments of it are pretty bad, and even some of the things you’ll find in journals are dodgy, so it’s hard to make concrete recommendations (other than my own book, of course…).