By what notion of ‘quantum state’? To the extent that both are simply collections of molecules in different arrangements, at least in principle it’s possible to write down a wave function, which of course can be in superposition.
I don’t believe in the Many Worlds interpretation. I admire it for its predictive power, and because it is free from certain drawbacks found in other interpretations.
It suffers from being difficult to demonstrate. Since the other worlds are absolutely isolated from us in all ways, it is pretty tough for anyone to prove that they do exist.
By and large, science doesn’t believe in its theories. Science believes in the raw data. Theories are either preferred or not, based on their ability to predict, and to endure challenges.
You might as well ask if we believe in Relativity. No: it may very well be supplanted by a more comprehensive theory, in which case it will be as dead as Newtonian dynamics. Meanwhile, it’s the last theory standing. All challengers have been shown inadequate.
The Many Worlds interpretation isn’t in that situation yet. It isn’t strong enough to assert superiority. It’s strong enough that a hell of a lot of us admire it, and some of us have an unscientific, emotional hope that it does rise to that level of prowess.
“A” universe? IMO, if this is true, then there are infinitely such universes - as well as infinitely such universes identical to ours, infinitely such universes that were identical to ours up to the point where I paused right…here, and so on.
I really don’t understand the physics. But I would say:
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Don’t confuse the scifi idea of parallel worlds with the quantum mechanical theory called “Many Worlds”. They’re sort of similar, but the first is mostly made up for plot reasons (like travelling through time, travelling faster than the speed of light, etc, etc) and like it or not, the second is an established idea in quantum mechanics. Lots of people think it’s wrong, but it’s not random bullshit.
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The more people know about quantum mechanics, and the more recently they learned quantum mechanics, the more likely they are to believe a many-worlds interpretation. This is obviously not conclusive, but it suggests a trend towards acceptance in the physics community. (Many people suspect the real answer will turn out to be “a bit like that but more complicated”, but it’s slowly gaining ground over the more traditional theories.)
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All physicists know what quantum mechanics will predict in a particular circumstance. There are several interpretations of what’s actually going on but they’re all unsatisfactory. Interpretations other than MW seem to have problems like “you have to know what counts as an ‘observer’” and “and then it goes backwards in time and arranges that the answer is what you expect”. MW has problems like “Splutter! Splutter! That’s inconceivable!”, but so have many previous theories that turned out to be correct like “the earth is not the centre of the universe” and “things get heavier the faster they go” and “the stars are REALLY REALLY far away” and “light sort of acts like a wave but always comes in little discrete packets”.
And FWIW, whichever you believe, there’s no experimental way of telling them apart, so in many ways it doesn’t matter.
Thank you for recommending this and the link as well.
A fine SF short story. Really good.
I sure hope that the many world hypothesis is wrong, precisely because of this issue.
I find the many worlds hypothesis utterly fascinating
Can someone explain what is this “many worlds interpretation” thing?
Clearly:D
I think people believe that a number of really smart theoretical physicists have posited a number of mathematical theories that seem to not rule it out.
But the question I have is if Many Worlds is more than just “mathematical masturbation”, where are these infinite worlds? Do they all sort of overlay each other? And if so, do they interact with each other? And why is our consciousness only in one of them at a time?
Funny that I found this thread, since my cat just demonstrated that the many world hypothesis is true.
Personnaly, I prefer strawberry flavoured ice cream.
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By that logic, an elephant in Africa can be in superposition with the Eiffel Tower. A cat has, what, 10[sup]27[/sup] atoms? There’s a reason classical mechanics works: quantum effects quickly become vanishingly small with increasing system size and/or temperature. The constant interactions preclude particles from occupying multiple states: it’s effectively an endless stream of measurements. The idea of writing down a wavefunction for a cat is thus silly, and even if you did, the probability of such a system existing in a superposition with another large, fundamentally different macroscopic object is so vanishingly small there aren’t enough zeroes to write it in decimal form.
The MWI is by definition untestable, and so by at least some definitions, it’s not science. It’s functionally equivalent to postulating the mind of God.
This is true for open systems, so the thought experiment is an idealization in that regard (hence, my caveat regarding ‘sufficient shielding’). But the conceptual issues are very real. Besides, for a completely shielded system, its macroscopic nature wouldn’t do anything to wash out quantum effects—it’s solely uncontrollabe interactions with an environment that carry of quantum coherences. And even in this case, it is in principle possible to account for the environment, and write down a quantum description. It’s true that the measurable proxies of quantumness—interference effects, for example—become small for large systems, but that doesn’t entail, for instance, that they can’t be in a superposition.
Most physicists would hold—and the theory itself claims—that quantum mechanics is in principle applicable on all size scales, and to all physical systems (the discipline of quantum cosmology is a testament to this). As I said, you’d have to explicitly modify the quantum dynamics in order to make the quantumness ‘go away’ for sufficiently large systems (the so-called GRW-theory is probably the most prominent example of this kind of this kind of ‘spontaneous collapse’-theory).
Doesn’t that many atoms constitute it’s own ‘environment’ though?
Plus, how do you shield something from the zero point field? That is going to be a source of random fluctuations and therefore a source of opportunities for decoherence.
No, they’re part of the system: decoherence only occurs if I ‘forget’ about something that has interacted with the system and ‘carried aways’ coherence information.
Well, since it’s a thought experiment, you can always engineer the system’s evolution such that it is unaffected by some kind of interaction (in jargon terms, the system’s Hamiltonian must commute with the interaction Hamiltonian). But even when that’s not done, I’m not sure it’s a factor: in order to effect decoherence of the system, the vacuum fluctuations would have to carry away information about the state of the system, such that making a measurement on the vacuum somewhere removed from the system would yield information about the state of the system, and I don’t see how that would work.
I think you’re confusing the ‘system’ with the ‘environment.’ AFAIK, there’s no prohibition against a random fluctuation causing the decoherence of any superposition for a randomly defined quantum system unless you’re saying, as you seem to be that the system and the environment are the same thing.
BTW, actual “measurement” isn’t required you know. I’m pretty sure any “disturbance” is sufficient.
No. If you’ve got the complete state of the system, and no external interactions occur, then there will be no decoherence. Mathematically, decoherence is a result of ‘tracing out’ (forgetting about) degrees of freedom that are irrelevant to the description of whatever you deem the ‘system’; this results (with a high likelihood for typical system-environment interactions) in a (mixed) state in which quantum coherences vanish. So if you have the complete state of the cat, any random bouncing of the cat’s atoms off of each other will not induce decoherence.
Only if you subsequently forget about whatever caused the disturbance; if you track it in your description, the composite system of ‘original system + whatever caused the disturbance’ will remain quantum coherent.