I think this question stems from a fundamental misunderstanding of the Everett interpretation...the idea of "many worlds" (a phrase I do not favor specifically because of this very misunderstanding!) evokes this imagery of an entirely new universe BURSTING forth dramatically upon the collapse of the wave function, and as an entirely new universe is "created," the amount of extent energy is literally doubled (or multiplied by many times more). Indeed, where does this energy come from?
What the Everett interpretation suggests is that in the same way you are comfortable with the function f(x)=y having (infinitely) many values (you don't HAVE TO choose an x, ie the function doesn't collapse), the wavefunction simply is what it is and doesn't collapse either. What we observe as the collapse of a function is simply an artifact of being a conscious being that can only observe one value of the of the wavefunction at any particular moment.
None of these unique values (observables) of the wave function can interact with each other (in the same way the value of x=2 doesn't "interact" with the value of x=8 for f(x)=y), so energy cannot be gathered or duplicated at any particular point of the wave function, so this energy creation/duplication is no issue.
The question is a misunderstanding. In the pure wave (Everett) interpretation, there are no universes being created when the wave function branches. Rather, different regions of the wave function become separated (decohered) from each other. https://physics.stackexchange.com/questions/41588/many-world...
Sean Carroll, following Everett, puts it in the most concise form: (i) systems are described by wave functions, (ii) wave functions obey the Schrödinger equation [1]. "Many-worlds", universes, observations, observers, and so on become just entia multiplicanda [2], superfluities.
[1] https://www.youtube.com/watch?v=nOgalPdfHxM, one set of rules in quantum mechanics at 36:00; at 1:13:14 where does the energy come from? energy of the set of all universes is conserved.
I think because of the abuse of "many worlds" in science fiction media (especially as of late) as a convenient plot device, people develop this idea that it's an unserious proposal wrt the foundations of physics. As far as I have read, it strikes me as perhaps the most parsimonious interpretation of QM out there.
Genuinely curious, what do you mean by "but you didn't say it couldn't be this, nanananana...?" The Everett interpretation isn't some fantastical notion spun up by a scifi writer...it is simply the consequence of removing collapse of the wavefunction as an objective event from the picture. And if it turns out our observations wouldn't be changed by removing this feature, then perhaps it was an extraneous feature in the first place!
Assuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious. There happens to be a model that fits some data, but that's it. It's a grotesque assumption to avoid a conflict in a man-made theory. It's a funny thought, but no more than that.
There's also nothing special about observing. Our consciousness isn't super-natural, so the idea is in desperate need of some other underpinning.
And probabilities: if this is one of many, many worlds, the distribution of events as we can observe them is heavily skewed. The next observations should follow a radically different pattern, unless you also assume that each split influences the probabilities of future events.
> Assuming many worlds, and many here means: enormous amounts, far exceeding the number of particles in the universe, is everything but parsimonious.
"Many worlds" is a misnomer. MWI is just wavefunction realism + unitary evolution. There's only one world, and really only one dynamical object: the wavefunction. It evolves according to some unitary operator, and that's the whole story. No splitting, no collapse, no objective classical transition, just quantum mechanics taken at face value.
Is it possible to observe anything at all in MWI? If yes, what does it mean to "observe something" in MWI? If not, is there any physical content in MWI?
Observations in MWI are just ordinary physical interactions. Specifically they're perturbative-regime interactions between the thing being observed and large thermalized systems (e.g. humans). From the perspective of the thermal bath, you get exponential suppression of everything but the eigenstates of the interaction Hamiltonian, which is why our observations "look classical".
Will other large thermalised system (e.g. rocks) also experience observations that "look classical"?
Another MWI proponent here is talking about how the "look classical" thing is "simply an artifact of being a conscious being that can only observe one value".
Is there something special about "large thermalised systems" (and/or humans)? How large have they to be to allow for "our observations"? Where is the boundary between the thing being observed and the observing thing?
MWI seems to still face most of the difficult questions - it not all.
> But they'll induce decoherence in the same way as a human, yes.
From the perspective (?) of the (non-human) thermal bath, will that decoherence result in a single (diagonal, mixture) state or in a particular state of those N separate states that would "look classical"?
Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is.
Depends on whether you're talking about the "perspective" of the whole joint |Rock>|Interaction Eigenstate 1> + |Rock>|Interaction Eigenstate 2> ... system or just one of its components.
> Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is.
Of course; but that's true of every scientific theory. Decoherence solves the preferred basis problem, not the hard problem of consciousness.
> Decoherence solves the preferred basis problem, not the hard problem of consciousness.
Ok, I guess I misunderstood the scope of "There's also nothing special about observing."
It's not clear to me if you (MWI) would say that rocks had defined positions when nobody was observing them - or whether the question of things having definite positions (and the very existence of those things) wouldn't even make sense in the absence of consciousness.
> Ok, I guess I misunderstood the scope of "There's also nothing special about observing."
There's nothing special about the physical processes constituting a scientific experiment. They're unitary evolution like everything else. Whether there's anything special about conscious experience (for my money: obviously yes) is outside the scope of physics.
> or whether the question of things having definite positions (and the very existence of those things) wouldn't even make sense in the absence of consciousness.
If you want to be perfectly precise, the MWI does not contain discrete things at all, any more than the Earth objectively has discrete continents and seas. But the most accurate map is not always the most useful one.
Correct, it is an enormous amount...Under Everett, the "number of worlds" practically exists on a continuous spectrum, so basically an infinitude of worlds. But this doesn't violate parsimony in terms of building a model of reality. I don't have the greatest comprehension of the history of science, but I imagine the behavior of water and gas was not initially explained as being the collective behavior of moles (6.02x10^23) and moles of individual molecules. The parsimony of thermodynamics is measured by the simplicity of the underlying equations that describe their behavior, not the staggering number of atoms involved.
As for observation, I didn't suggest there was anything special about observing. In fact, this is part of what makes Everett among the most parsimonious interpretations: While some (not all) other interpretations are tasked with explaining the nature of observation (what counts as observation, how quickly does collapse propagate, etc), under Everett, there is no notion of observation at all. My point about consciousness is that, being conscious, we are forced to have a point of view which depends on where we exist in/on the wave function. I wasn't suggesting that consciousness has any actual effect whatsoever on the wavefunction.
I admit that the nature of probability is among the most difficult parts of Everett to wrestle with, though I'm not sure I understand why subsequent observations should follow a radically different pattern? It's still the same wavefunction with the same distributions as before...Schrodinger's equation is the same wherever you are on the wavefunction.
Many worlds just falls out of superposition and entanglement. Those happen in quantum systems, and we are made of quantum systems. To avoid that you have to stipulate something additional that avoids putting macroscopic objects like devices, cats and brains into superpositions.
> it is simply the consequence of removing collapse of the wavefunction as an objective event from the picture. And if it turns out our observations wouldn't be changed by removing this feature, then perhaps it was an extraneous feature in the first place!
> What we observe as the collapse of a function is simply an artifact of being a conscious being that can only observe one value of the of the wavefunction at any particular moment.
If we simply assume that our observations are as if a wave function happened we can indeed have our Schrödinger cake and eat it too.
