We were briefly discussing the universal wave function the other day, and I questioned whether such a critter is really real.
This fellow suspects not, and he’s certainly not the only one:
The idea that the universe splits into multiple realities with every measurement has become an increasingly popular proposed solution to the mysteries of quantum mechanics. But this “many-worlds interpretation” is incoherent, Philip Ball argues in this adapted excerpt from his recent book Beyond Weird.
…..The MWI is surely the most polarizing of interpretations. Some physicists consider it almost self-evidently absurd; “Everettians,” meanwhile, are often unshakable in their conviction that this is the most logical, consistent way to think about quantum mechanics. Some of them insist that it is the only plausible interpretation — for the arch-Everettian David Deutsch, it is not in fact an “interpretation” of quantum theory at all, any more than dinosaurs are an “interpretation” of the fossil record. It is simply what quantum mechanics is. “The only astonishing thing is that that’s still controversial,” Deutsch says.
My own view is that the problems with the MWI are overwhelming — not because they show it must be wrong, but because they render it incoherent. It simply cannot be articulated meaningfully.
I’ll attempt to summarize the problems, but first, let’s dispense with a wrong objection. Some criticize the MWI on aesthetic grounds: People object to all those countless other universes, multiplying by the trillion every nanosecond, because it just doesn’t seem proper. Other copies of me? Other world histories? Worlds where I never existed? Honestly, whatever next! This objection is rightly dismissed by saying that an affront to one’s sense of propriety is no grounds for rejecting a theory. Who are we to say how the world should behave?
A stronger objection to the proliferation of worlds is not so much all this extra stuff you’re making, but the insouciance with which it is made. Roland Omnès says the idea that every little quantum “measurement” spawns a world “gives an undue importance to the little differences generated by quantum events, as if each of them were vital to the universe.” This, he says, is contrary to what we generally learn from physics: that most of the fine details make no difference at all to what happens at larger scales.
But one of the most serious difficulties with the MWI is what it does to the notion of self. What can it mean to say that splittings generate copies of me? In what sense are those other copies “me?”
Brian Greene, a well-known physics popularizer with Everettian inclinations, insists simply that “each copy is you.” You just need to broaden your mind beyond your parochial idea of what “you” means. Each of these individuals has its own consciousness, and so each believes he or she is “you” — but the real “you” is their sum total.
There’s an enticing frisson to this idea. But in fact the very familiarity of the centuries-old doppelgänger trope prepares us to accept it rather casually, and as a result the level of the discourse about our alleged replica selves is often shockingly shallow — as if all we need contemplate is something like teleportation gone awry in an episode of “Star Trek.” We are not being astonished but, rather, flattered by these images. They sound transgressively exciting while being easily recognizable as plotlines from novels and movies.
Tegmark waxes lyrical about his copies: “I feel a strong kinship with parallel Maxes, even though I never get to meet them. They share my values, my feelings, my memories — they’re closer to me than brothers.” But this romantic picture has, in truth, rather little to do with the realities of the MWI. The “quantum brothers” are an infinitesimally small sample cherry-picked for congruence with our popular fantasies. What about all those “copies” differing in details graduating from the trivial to the utterly transformative?
……Consciousness relies on experience, and experience is not an instantaneous property: It takes time, not least because the brain’s neurons themselves take a few milliseconds to fire. You can’t “locate” consciousness in a universe that is frantically splitting countless times every nanosecond, any more than you can fit a summer into a day.
One might reply that this doesn’t matter, so long as there’s a perception of continuity threading through all those splittings. But in what can that perception reside, if not in a conscious entity?
And if consciousness — or mind, call it what you will — were somehow able to snake along just one path in the quantum multiverse, then we’d have to regard it as some nonphysical entity immune to the laws of (quantum) physics. For how can it do that when nothing else does?