What’s the Difference Between Copenhagen and Everett?
math.columbia.edu
math.columbia.edu
https://wiki.lesswrong.com/wiki/The_Quantum_Physics_Sequence
According to Everett / Decoherence interpretation, as explained by Eliezer, atomic or subatomic particles are not physically real—let alone macroscopic objects made with them.
What's physically real is the single amplitude distribution over the infinite-dimensional mathematical space of all possible joint configurations of all the particles in the universe. This distribution—as well as boggling the mind—is complex-valued, continuous, differentiable, and evolving with time according to the well known QM equations. Crucially, it may be more or less factorizable over any given subset of its infinitely many dimensions.
"You" and "me" are just two (more or less) factored subspaces of The amplitude distribution.
Therefore, the question of where do the Born probabilities come from (an open question in QM) is shown to be inextricably linked to an understanding of the physical basis of consciousness (another big open question.) The Born probabilities may represent the "amount of consciousness" (of "you", the observer) that is split among newly factored subspaces, every time "you" get further fragmented, aka. decohered, aka. "entangled" with new blobs of amplitude.
I cannot recommend Eliezer's series of articles highly enough.
This is the narcissist interpretation of quantum mechanics. No object constancy, quantum consciousness, Hume's "I believe it when I see it" are all narcissist perspectives on objects.
Realism vs. subjectivism might be a false dichotomy in the quantum realm, hiding alternative narratives. For example, perhaps the measurement problem is able to give us a notion of true objects, as opposed nebulous clouds of atoms, where objects are strongly entangled internally and until they are entangled with each other they almost exist in separate realities. Background to this idea is back holes being the fastest scramblers of information, my limited understanding, and wild imagination.
The problem is that it's unbounded. It's not just about specific measured quantum events, because that begs the question about how and where and why universes branch off.
Without that foundation, it becomes about all possible quantum events. Literally. Any moving particle that has a chance to decay may decay at any time, spawning a universe. And some of those spawned interactions will lead to other spawned interactions...
Somehow you have to get the Born Rule from a number of possible interactions that is so big it reduces the number of particles in the universe to an insignificant rounding error.
Assuming this number is even countable (up for debate) there must be universes in which quantum physics doesn't appear to work as it does here.
You can't just assume that somehow you get the right answer with a nice converging integral. Because the complete list of possible MWI universes includes a very small - but not zero - number where consistently unlikely interactions are the norm, so they operate with the "wrong" laws - for example neutrons that refuse to decay, or gluons that stay permanently glued.
Which being the case, we don't know whether this universe is a probabilistic freak and the "real" laws are different to the ones we see here. Maybe our Born Rule is the freak, and most universes operate differently. With MWI, there's no way to tell.
And so on for other issues. MWI is best left to science fiction plot lines. I really can't see it making sense as either falsifiable science or consistent philosophy.
Branching an emergent property of large systems. Consider the following:
* I have a qbit in a superposition for 0 and 1
* I as a large, hot, wet macroscopic system interact with that qbit in such a way that my future behaviour depends on the state of that qbit (say if I measure it to be 1 I shoot myself and if I get 0 I go for a walk)
If I try to measure the qbit, I become entangled with it. According to unitary evolution, my wave function would be an entangled superposition of the two events. However, for macroscopic systems entanglement and superpositions are basically meaningless. I couldn’t do an interferometry experiment on my body that would determine if I’m in a entangled state so a many worlds person would say that the wave function of be unvierse has effectively branched into two parts that never very little overlap or influence on each other.
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Maybe this analogy will help: If I have a cup of water and we look at it on a macroscopic scale, there’s a very clear difference between the liquid and the air above it. There’s a division. However, if you zoom in, that division becomes very fuzzy. There’s a region near the waters surface where air molecules and water molecules freely mix and interact and there’s actually a somewhat smooth crossover between the air and water. So the phase separation between a cup of water and the air above it isn’t a fundamental part of the rules of physics. It’s just an emergent behaviour like the branching of the wave function.
However, if you knew about the entire wavefunction as an outside godly observer to the universe might, then there’d be no point in speaking of ‘branches’.
So? A priori there's nothing to judge this as strange...
There's recently been a long thread over on PhysicsForums[1] about the Wiegner's friend experiment[2]. The thread was kicked off by this[3] paper detailing a realization of the experiment, in which the authors conclude "this result lends considerable strength to interpretations of quantum theory already set in an observer-dependent framework and demands for revision of those which are not."
Then again as far as I can see MWI doesn't come out victorious, "one way to accommodate our result is by proclaiming that “facts of the world” can only be established by a privileged observer—e.g., one that would have access to the “global wavefunction” in the many worlds interpretation".
Then again I haven't studied QM so what do I know. Fun to think about while on the bus tho!
[1]: https://www.physicsforums.com/threads/a-realization-of-a-bas...