One of the greatest threats to our shared reality (along with "social media") is "the multiverse hypothesis," or the view, roughly, that every time a particle goes through a slit, or something else happens, the universe multiplies by fission, with each branch (quadrillions of them or so every instant in every square millimeter of space) entirely sealed off from the others. We might state the hypothesis as follows: every possible world is actual.
By way of contrast, I assert that there’s exactly one world, and that the multiverse is baldly ridiculous on many grounds. There should be no question of accepting something that rococo until there’s absolutely no other way to read the data. There must be, because this one, while fun, is false and repulsive.
In honor of Everything Everywhere All at Once, which won some Oscars last night, and the Marvel non-universe, I'm taking quick crack.
Let's define “universe” in the traditional fashion: all that is. That there’s only one universe is a matter of definition, as indicated by the prefix “uni.” The universe = all that exists is a stipulated definition, not an empirical assertion. It's not the kind of thing that could be discovered to be false, any more than you could discover an island of married bachelors (it might be fun to go to an island of merry bachelors, though, which is perfectly possible). Or if you want to shift the meaning of “universe” so there can possibly be more than one, I’ll coin a new term for the reality that contains them all.
The view is that the universe consists of quintillions of bubble-like sub-universes.
In this universe, I made a decision to eat granola rather than cornflakes about a half hour ago. Right there, the universe branched off (actually it branched off sextillions of times as "the spoon" rose to "my" "lips"). In one bubble, I ate granola. In another I didn’t. So in the system that contains them both I ate granola and didn’t. The multiverse hypothesis asserts of septillions of propositions that both that proposition and its negation are true. Or it asserts that all reality is a tissue of contradictions, that no empirical assertion is true that isn’t false.
It’ll require a long self-discipline to accept that, and when you have you’ll be as extremely irrational as it’s possible for a person to be. And now you really do have some problems of theory choice, having abandoned all rational criteria. Are you sure you had good enough reasons to do so?
Perhaps it’ll be said by my opponents (who passionately endorse and passionately disagree with the position they put forward), truth is relative to bubbles: the proposition is true in bubble a and false in bubble b. It's true in (a) that I ate granola, in (b) that I ate cornflakes (in (c) that I slept in, in (d) that I was fasting etc.). So was it or was it not me who ate cornflakes in universe (b)? If I’m right now inhabiting multiple (octillions) of universes, then I’m located in multiple spaces and times simultaneously, contrary to anything I can empirically detect. Also, I’m right now eating and failing to eat granola. I’m simultaneously alive and dead, and I don't mean that as some sort of artsy metaphor. I both exist and never existed on this view.
If any given entity can appear on more than one universe, then the system as a whole manifests nonillions of logical contradictions: the whole’s completely incoherent. This reality isn’t the sort of thing that could be studied by science. If the very same entity can’t appear in more than one universe, then the multiverse hypothesis can’t explain double slit experiments or anything else. It's not at all about, for example, different routes taken by the same particle, or different breakfasts eaten by the same person.
Compressing: If the same entity can exist in different universes then [they're not different universes and] quindecillions of logical contradictions are true. If the same entity can’t exist in different universes then the multiverse hypothesis can’t underpin or explain this reality. The picture of forking possibilities falls apart completely. Solve this dilemma before you continue, physicists.
A couple of quick observations. First, the multiverse hypothesis yields, very precisely, the least elegant ontology. Of all the possible theories of anything that have ever been put forward by anyone in any universe, the multiverse maximally violates Ockham's razor, or the principle that the simplest explanation is to be preferred, or "do not multiply entities without necessity." But Stephen Hawking, for example, endorses Ockham's razor as the fundamental criterion of theory choice in one chapter, and in the next he endorses the multiverse hypothesis. It makes you realize that being really good at math doesn't necessarily help you make sense on other matters.
Hawking seems to believe that "the" "universe" originated in a big bang and is expanding. Perhaps Brian Greene and Neil DeGrasse Tyson agree with him? But they also accept the multiverse hypothesis, so they agree and disagree. They think that reality originated in a big bang and that it didn’t. It's hard to disagree with that, but also impossible not to.
How certain physicists cornered themselves into this maximally incoherent non-explanation, I’m not entirely certain. But I assert that there should’ve been a reality in which other explanations of double slits or cats in boxes were fully explored before we just went for full-bore irrationalism.
Meanwhile, let's affirm the one reality we all share, the only reality that can be known to exist.
—Follow Crispin Sartwell on Twitter: @CrispinSartwell