Quantum Filioque

You will never die, for some value of "you"

Whenever I talk about quantum physics in connection with fiction, I make a point of plugging the short story “Divided by Infinity” by Robert Charles Wilson, which I often call out as the best presentation of the Many-Worlds Interpretation (the more popular term for the Everett interpretation I discussed last week) in fiction. Most stories relying on the multiversal aspect of the theory cheat really badly by having characters move between “universes,” but “Divided By Infinity” gets points for keeping that to an absolute minimum. There’s a little bit of cross-talk— some mysterious books that come and go— but it stays in one place to an admirable degree.

Photo by MW on Unsplash

The main reason I highlight it, though, is that it really runs with the logic of the theory, in a deeply disquieting way. The pivotal moment in the story is when the narrator gets a copy of a book called You Will Never Die by Carl G. Soziere, which lays out a version of Many-Worlds that plays up the role of conscious perception in separating the branches of the wavefunction. The title, in the context of the story, is an objective fact: the different “worlds” of the interpretation are distinguished by a given observer perceiving different outcomes of particular measurements, and since death is the cessation of consciousness, you will never perceive a world in which you die. And this is not necessarily a Good Thing…

The presentation in the story isn’t especially rigorous, but in a way that fits with the characters¹, but it gets at something real. In some sense, it takes the logic of the theory more seriously than some of its high-profile proponents— I read something by Max Tegmark where he was furiously back-pedaling away from the Soziere conclusion, saying something “Well of course, as we age, there must be some degradation of consciousness so that nobody’s actually going to live forever…” Which struck me as funny considering how he’s notable for pushing a really expansive multiverse cosmology, to the point of attributing (some level of) reality to abstract mathematical constructs. But immortality is a bridge too far?

I bring this up partly because I plugged the story in my Oslo talk, but mostly because when I promoted last week’s post on Bluesky, I got in a bit of back-and-forth with Philip Ball about this. And he’s really opposed to the “multiple observers” thing that’s central to many presentations of Everettianism, including the one Wilson dramatizes.

I couldn’t respond at length on Bluesky because I had to teach that day, but even with more time to consider, I’m not sure I can formulate an adequate response. Mostly because I don’t really grasp the core issue, here. This is not a new problem— it comes up basically every time I dip into the never-ending arguments about quantum foundations— but I just don’t personally understand why this is such an intensely partisan issue. As I said in the thread, this feels a bit like a “filioque” thing, referring to the one-extra-word issue that’s at the core of a thousand-year schism between Roman Catholic and Eastern Orthodox churches. It’s expressing a doctrinal difference that’s incredibly significant to the people involved in the argument, but that seems bafflingly abstruse to someone not deeply committed to one of the traditions. When most modern folks run across that particular bit of church history, the reaction is generally “Wait, what? Why’s that the sticking point?”

In a weird way, I have a better feel for the origin of one of the objections to Everettianism that, to my mind, is more wrong— people who misread it as a physical doubling of universes. I understand a vehemently negative reaction to the idea that, at the instant of opening the box, you would create a nearly-exact copy of everything differing only in the state of one particular cat. The notion that you now have two sets of the atoms corresponding to the cat, the box, the hapless grad student charged with cleaning the litter box, etc. is absurd and objectionable. It’s also, as I tried to lay out in the post last week, not what the theory actually says²— there is one and only one set of atoms corresponding to All The Things, but they’re in an endlessly expanding entangled superposition state. We can choose to subdivide that superposition state into discrete “branches” corresponding to different definite outcomes of the experiment, but that’s a matter of mathematical convenience.

Once you’re there, though, I don’t understand where the objection to “multiple observers” comes from, or why it’s quite so vehement. If we’re going to subdivide the entangled superposition of the one set of atoms corresponding to the whole Schrödinger cat experiment into different branches, one piece of that superposition is going to correspond to a state where the collection of atoms corresponding to the grad student is happily scritching the ears of the lab feline, and another piece is going to correspond to the same student sadly filling out biohazard disposal paperwork. That’s an inevitable consequence of the logic of just letting everything evolve according to the Schrödinger equation.

I feel like there’s some missing axiom at work here that I’m just not getting. Something in the Cartesian dualism sort of vein, where conscious perception is assigned a status that’s not purely physical, maybe? I don’t really know. It seems to me that if you’re willing to accept that a concept as slippery as “consciousness” is associated with a particular physical arrangement of atoms, though, and those atoms are allowed to be in complicated entangled superpositions, then of course you’ll have different pieces of the superposition that correspond to different perceptions of the universe. I don’t know how else you could avoid that conclusion except by denying that “consciousness” is a physical thing. But then I don’t really get the objection to “filioque,” either…

I guess the other option is that it’s simply an unappealing conclusion— that is, an aesthetic judgement. Which, you know, de gustibus³, and all that. If you’re bothered by the thought of other versions of yourself experiencing different versions of reality, then, yeah, Everettianism probably isn’t for you. But then, to loop back to Max Tegmark and his levels of multiverses for a second, you should probably take a pass on inflationary cosmology as well, for more or less the same reason. There are only so many ways to put atoms and molecules together, after all, so logic dictates that somewhere Out There, some mind-bogglingly huge distance from Earth, there must exist a collection of atoms that’s nearly identical to our planet except for one particular cat.

In both cases, I think the logic leading to the conclusion that there should be “other versions of you” Out There somewhere is pretty solid, but there also isn’t any solid experimental evidence forcing you to accept the core premise. In which case, you’re free to make some other choice of how to think about the deep structure of the universe. With the understanding that that other choice will have some implications⁴ that other people will find unappealing and reject, possibly with some vehemence. Until and unless somebody devises and performs an experiment that can conclusively settle either of these, there’s room for the exercise of personal taste.

I realize that this is not likely to convince anybody, but I honestly just don’t get what the problem is at a level where I could start to build a convincing argument. Unlike the objection rooted in the misunderstanding involving a physical doubling of things, it’s not an objection I ever had myself, so I don’t understand it from the inside, and thus can’t construct an chain of logic to lead out of it. All I can say is “Yeah, that’s pretty much what you’re stuck with,” and try to get on with the rest of my day.

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That’s this week’s entry in “Why I Am Not a Philosopher.” You just need to embrace the inevitability that in some branch of the wavefunction of the universe you’ll click this button:

And also this one, because the comments will be open:

1. This is a regular thing in Wilson’s fiction, and why he’s one of my favorite contemporary-ish authors. He never has the sort of hypercompetent point-of-view character who fully understands all the speculative science and technology, and as a result dodges a lot of the usual pitfalls relating to technical accuracy that undermine “hard SF” for me.

2. Subject to the usual disclaimers about this being my personal reading of the theory, etc. etc.

3. Banner day for dropping bits of Latin shorthand on the blog, apparently…

4. Some sort of collapse mechanism for QM, some kind of “fine-tuning” in cosmology.