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by T-A
4027 days ago
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Quantum decoherence != multiverse, and the multiverse interpretation of quantum mechanics != the multiverse of cosmology mentioned in this essay. The latter is a rather more concrete affair, basically saying that in regions of the universe too far away to be observable, the parameters of low energy physics (kinds of particles, strengths of interactions between them) can be different from what we see in our region; rather than being fundamental properties of physics, they were picked randomly (by physical processes) at the big bang. If they are not fundamental properties of the theory, there is no need to come up with a theory which explains their values (the fine-tuning problem mentioned in the essay); we live in a region where the values are such that our existence is possible, because that is the only possibility. In regions where the values do not allow the existence of observers capable of asking "why are the values such that I can exist?", there are no observers asking "why are the values such that I can exist?". Some call this idea (the anthropic principle) neat, others call it a cop-out and point out that since the postulated regions with different physical parameters can not be observed, the whole construction falls outside the scope of empiricism, and so can not be science (as traditionally understood). Hence essays such as this... |
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I did imply I did not know what multiverse was being considered. As far as I can tell, the article did not say which multiverse it was talking about. There are many reasons to believe in an… unbelievably large universe:
1) Beyond the observable universe. Beyond a certain limit, the universe expands so fast that even light from there can't reach us, ever. Beyond that limit, it might as well be another universe. But whatever lies beyond that limit aren't additional entities. They're just the consequence of known laws of physics. Positing that they somehow don't exist would form an additional assumption in the theory, and therefore not good from an Occam's razor perspective.
2) Inflation. Would apparently create a number of "bubbles" or something, that are sufficiently far a part not to observe each other. I can't judge this one.
3) Macroscopic decoherence. The particle is in in a superposition of being destroyed/intact, the cat is in a superposition of being dead/alive, the scientist that observe the cat is in a superposition of mourning/petting the cat… Well, the Many World Interpretation of quantum mechanics. Well, that's what we call the Many World Interpretation of quantum mechanics. Again, no additional entity here: the other universes are just a natural consequence of long known equations. If anything, we remove an entity, compared to the Copenhagen interpretation: that pesky collapse.
4) Tegmark's level IV multiverse, where every possible mathematical construct "exists" in some sense, and our universe is just one of them (which also happen to support sentient life). Right now, I don't know what to think of it. Though it would be incredibly convenient, from an anthropic principle stand point.
> since the postulated regions with different physical parameters can not be observed,
Are we postulating the regions, or are we postulating a large universe with changing parameters? This is not the same thing. The former is obviously incredibly complex, and therefore a priori impossibly improbable. The latter doesn't involve that many entities, and may even be simpler than current mainstream theories. Or it may not. I'm not a physicist.