Many-worlds interpretation: Worlds joining instead of splitting?

[Meatbot]

If two branches of the tree eventually came to be identical would they join or would they continue to exist as separate worlds? If they joined, observers in each would remember a different history. Any connection between this and relativity where people observe the same event happening in different ways?

What if in the far future all branches converge?

 

[vanesch]

"branches to join" is nothing else but quantum interference. In order for "branches to join", the two components of the statevector that represent them, and happen to be in different "classical subspaces" need to evolve into a common "classical subspace". The component that matters in that subspace is then nothing else but the sum of the two former components. In the making of this sum, interference phenomena will probably occur.

Experiments that put this to work on a microscopic scale are the famous so-called delayed quantum eraser experiments. That said, they don't *prove* any "many worlds" view on quantum theory. They can be conveniently explained in such a view, but they don't prove it. It is even more speculative to assume that these many world phenomena persist on the macroscopic scale, although at present there is no experimental evidence *against* it.

Experimental evidence against many worlds would be: the failure of quantum interference on a certain scale. Many worlds is simply assuming quantum interference and superposition universally.

 

[dlgoff]

" Experimental evidence against many worlds would be: the failure of quantum interference on a certain scale."

Could you explain? I don't understand "certain scale".

Nice to hear from you here.

Regards

 

[vanesch]

" Experimental evidence against many worlds would be: the failure of quantum interference on a certain scale."

Could you explain? I don't understand "certain scale".

"scale of macroscopicity", whatever that is: gravitational mass, size, time scale, ...

If you expect, taking into account all possible effects of decoherence, some quantum interference effect, and you don't see it, then quantum mechanics on that scale is falsified, and hence MWI (on that scale).

 

[dlgoff]

Okay, I see what you mean. Thank you.

 

[michael879]

This is an interesting idea. I am not sure if it has any relevance but its a cool thought. If you shoot 2 electrons at a double slit and measure where they hit on the screen, your in two different worlds simultaneously. The one where electron 1 hit point 1 and electron 2 hit point 2, and the one where electron 1 hit point 2 and electron 2 hit point 1. I am not sure if in this case the worlds split and then rejoin, but I am sure there's some experiment that could cause that to happen.

 

[vanesch]

This is an interesting idea. I am not sure if it has any relevance but its a cool thought. If you shoot 2 electrons at a double slit and measure where they hit on the screen, your in two different worlds simultaneously. The one where electron 1 hit point 1 and electron 2 hit point 2, and the one where electron 1 hit point 2 and electron 2 hit point 1. I am not sure if in this case the worlds split and then rejoin, but I am sure there's some experiment that could cause that to happen.

Actually, no, and that's because electrons are indistinguishable particles, so the state "electron 1 hits point 1 and electron 2 hits point 2" is exactly the same state (in projective hilbert space) as the state "electron 1 hits point 2 and electron 2 hits point 1".