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I’m a “believer” in the Everett Interpretation (on the grounds that it’s the simplest interpretation) but I can’t see how such an experiment could prove anythin

by rvcdbn 3y ago

I’m a “believer” in the Everett Interpretation (on the grounds that it’s the simplest interpretation) but I can’t see how such an experiment could prove anything. This experiment seems to assume we can keep the whole apparatus including the Geiger counter and the mechanism to move the cannon ball from becoming entangled with the environment (decohering). This seems very far outside the realm of current technology.

btilly 3y ago
It shows that when there is a superposition of quantum mechanical states, you also get a superposition of two different space-time structures. The reason why the Everett Interpretation is needed for the experiment to be valid is that according to it decoherence results is a superposition of quantum mechanical states, and not a collapse. If you believe in another interpretation, there has been a collapse, and so the experiment demonstrated nothing.
- rvcdbn 3y ago
  Once decoherence has occurred I don’t think it’s meaningful to say that the system exists in a superposition of states. The multiple decohered branches of the wave function can no longer interfere with each other and so there’s no way for them to affect each other, which is why we call them separate worlds. Within each decohered branch there’s an experimental apparatus and a human that sees one specific outcome. This was Everett’s main insight that each observer in each branch experiences what looks like a collapse but is really just their brain becoming entangled with one or other of the measurements.
  - btilly 3y ago
    According to quantum mechanics, they can no longer interfere with each other. But we are bringing gravity into the mix. Gravity works differently than the other forces. Do space-time structures also exist in a superposition of states? Or does QM work against an essentially classical gravitational space-time background? Without a theory combining quantum mechanics and gravity, the answer is not obvious. The fact that the superpositions do NOT interfere gravitationally means that either there was no quantum mechanical superposition (collapse actually happened) or that gravity can also exist in superimposed states. If you believe in the Everett interpretation, then there must have been a quantum mechanical superposition, and this tells us something non-trivial about a quantum theory of gravity.

by rvcdbn 3y ago

btilly 3y ago

It shows that when there is a superposition of quantum mechanical states, you also get a superposition of two different space-time structures. The reason why the Everett Interpretation is needed for the experiment to be valid is that according to it decoherence results is a superposition of quantum mechanical states, and not a collapse. If you believe in another interpretation, there has been a collapse, and so the experiment demonstrated nothing.

rvcdbn 3y ago
Once decoherence has occurred I don’t think it’s meaningful to say that the system exists in a superposition of states. The multiple decohered branches of the wave function can no longer interfere with each other and so there’s no way for them to affect each other, which is why we call them separate worlds. Within each decohered branch there’s an experimental apparatus and a human that sees one specific outcome. This was Everett’s main insight that each observer in each branch experiences what looks like a collapse but is really just their brain becoming entangled with one or other of the measurements.
- btilly 3y ago
  According to quantum mechanics, they can no longer interfere with each other. But we are bringing gravity into the mix. Gravity works differently than the other forces. Do space-time structures also exist in a superposition of states? Or does QM work against an essentially classical gravitational space-time background? Without a theory combining quantum mechanics and gravity, the answer is not obvious. The fact that the superpositions do NOT interfere gravitationally means that either there was no quantum mechanical superposition (collapse actually happened) or that gravity can also exist in superimposed states. If you believe in the Everett interpretation, then there must have been a quantum mechanical superposition, and this tells us something non-trivial about a quantum theory of gravity.