I In the many worlds interpretation, how do the worlds join?

[sahashmi]

TL;DR Summary

How do the worlds join in entanglement?

In the many worlds interpretation, how do the worlds join?

In the case of perfect anticorrelation in quantum entanglement, where one particle being spin up implies the other is spin down, what exactly is happening in the MWI?

If Alice observes spin up, she enters the world where Bob sees spins down. If she observes spin down, she enters the world where Bob sees spin up.

But what prevents Alice after observing spin up from entering a world where Bob sees spin up? Presumably, this is because of the conservation of momentum? If so, how is this enforced non locally? I’m just having trouble understanding how the many worlds interpretation keeps everything still local

 

[PeroK]

MWI is essentially just an evolving wavefunction, which evolves according to the laws of QM. It doesn't do anything special to ensure anticorrelarion of an entangled spin state. That's part of the laws governing wavefunction evolution.

Your hypothesis of people jumping around between "worlds" doesn't make much sense.

What is your source for the MWI interpretation?

 

[sahashmi]

MWI is essentially just an evolving wavefunction, which evolves according to the laws of QM. It doesn't do anything special to ensure anticorrelarion of an entangled spin state. That's part of the laws governing wavefunction evolution.

Your hypothesis of people jumping around between "worlds" doesn't make much sense.

What is your source for the MWI interpretation?

Here is what I don’t understand. Imagine if both Bob and Alice can pick either the X or Y axis as a measurement choice. Let’s assume the spins are anti correlated.

If they both pick the X axis, the possibilities are (+,-) or (-,+).

If they both pick different axes, the possibilities are (+, +), (-,-), (+, -), and (-,+).

So depending on the measurement choice, there are either 2 worlds or 4 worlds. Where is this splitting process happening and when? How does it know how many worlds are being generated?

 

[Nugatory]

How does it know how many worlds are being generated?

We have a wave. It evolves according to Schrodinger’s equation. There’s nothing to “know”, any more than a water wave evolving according to the laws of hydrodynamics “knows” to spread in one direction or another according to the shape of the coastline it encounters.

 

[pines-demon]

Here is what I don’t understand. Imagine if both Bob and Alice can pick either the X or Y axis as a measurement choice. Let’s assume the spins are anti correlated.

If they both pick the X axis, the possibilities are (+,-) or (-,+).

If they both pick different axes, the possibilities are (+, +), (-,-), (+, -), and (-,+).

So depending on the measurement choice, there are either 2 worlds or 4 worlds. Where is this splitting process happening and when? How does it know how many worlds are being generated?

The splitting happens at the measurement, Bob and Alice get entangled with the particles involved.

 

[Yaroslav Granowski]

>In the many worlds interpretation, how do the worlds join?

By being identical.
Think about time reversibility:
Forward: One world splits into two that differ only by the spin of the particle.
Backward: Two worlds that differ only by the spin of the particle join into one.

You may have them separated by several steps - that's how quantum computer operates.
But you can forget about communicating with your alter-ego from parallel universe like in some movies

 

[jacobbry]

>In the many worlds interpretation, how do the worlds join?

By being identical.
Think about time reversibility:
Forward: One world splits into two that differ only by the spin of the particle.
Backward: Two worlds that differ only by the spin of the particle join into one.

You may have them separated by several steps - that's how quantum computer operates.
But you can forget about communicating with your alter-ego from parallel universe like in some movies

>In the many worlds interpretation, how do the worlds join?

By being identical.
Think about time reversibility:
Forward: One world splits into two that differ only by the spin of the particle.
Backward: Two worlds that differ only by the spin of the particle join into one.

You may have them separated by several steps - that's how quantum computer operates.
But you can forget about communicating with your alter-ego from parallel universe like in some movies

The many worlds interpretation is predicated on the assumption of infinite worlds and isn’t plausible without infinite worlds however due to the nature of infinity an infinite number of worlds would undergo the process you have mentioned all the time of joining and separating however what I think is important to understand is that if two “worlds” where to separate than unlike the movies and such they wouldn’t just become two different “worlds” but will always have been two different “worlds” and if they join then they were never two “worlds” this interpretation means that the infinite number of worlds exactly like ours are in fact only one world.

 

[DaveC426913]

The many worlds interpretation is predicated on the assumption of infinite worlds and isn’t plausible without infinite worlds however due to the nature of infinity an infinite number of worlds would undergo the process you have mentioned all the time of joining and separating however what I think is important to understand is that if two “worlds” where to separate than unlike the movies and such they wouldn’t just become two different “worlds” but will always have been two different “worlds” and if they join then they were never two “worlds” this interpretation means that the infinite number of worlds exactly like ours are in fact only one world.

Punctuation! I almost passed out just reading that!

 

[jacobbry]

Punctuation! I almost passed out just reading that!

Sorry I’m extremely dyslexic you realise you can breathe even when I haven’t put punctuation.

 

[PeterDonis]

The many worlds interpretation is predicated on the assumption of infinite worlds

No, it's not. "Many worlds" is actually a misleading name. There is only one wave function in the MWI. The "worlds" are just particular branches of the entangled wave function. There is no "assumption of infinite worlds" anywhere.

The rest of your post looks like, at best, a version of pop science mythology about the MWI.

 

[PeroK]

Sorry I’m extremely dyslexic you realise you can breathe even when I haven’t put punctuation.

The real problem is the dodgy physics you posted.

 

[PeroK]

Here is what I don’t understand. Imagine if both Bob and Alice can pick either the X or Y axis as a measurement choice. Let’s assume the spins are anti correlated.

If they both pick the X axis, the possibilities are (+,-) or (-,+).

If they both pick different axes, the possibilities are (+, +), (-,-), (+, -), and (-,+).

So depending on the measurement choice, there are either 2 worlds or 4 worlds. Where is this splitting process happening and when? How does it know how many worlds are being generated?

I'm not an advocate of MWI. I'm agnostic about QM interpretations. But, MWI explains non-locality and entanglement better than many other interpretations.

In MWI there is only the wavefunction evolving in Hilbert space. Non-locality is naturally part of the mathematics. Mathematics itself is not restricted to physically local interactions.

If you think non-locality is a problem.in MWI, then you have not understood MWI at all.

The issues with MWI lie elsewhere. In justifying the Born rule, for example.

 

[Yaroslav Granowski]

The many worlds interpretation is predicated on the assumption of infinite worlds and isn’t plausible without infinite worlds

It could be an inifinitely large number that isn't an infinity. And I don't see how it is relevant.

>due to the nature of infinity an infinite number of worlds would undergo the process you have mentioned all the time of joining and separating

There is no "process" of joining and separating. This is just an interpretation of how states relate to each other.
Some other interpretation could think in terms of coordinates of some high-dimensional space. If two worlds of MWI differ only by the spin of one particle - it can be interpreted that these worlds are two vectors in that space, which differ only by one coordinate.

>this interpretation means that the infinite number of worlds exactly like ours are in fact only one world.
Indeed.

 

[PeterDonis]

It could be an inifinitely large number that isn't an infinity.

This is nonsense.

If two worlds of MWI differ only by the spin of one particle - it can be interpreted that these worlds are two vectors in that space, which differ only by one coordinate.

That's not what "worlds" are in the MWI.

 

[Yaroslav Granowski]

This is nonsense.

The infinity of the universe is just a conjecture, not a proven theory.

That's not what "worlds" are in the MWI.

Of course. This was an example of "Some other interpretation..."

 

[weirdoguy]

The infinity of the universe is just a conjecture, not a proven theory.

What it has to do with what you wrote eralier? And what you wrote earlier is nonsense mathematically.

 

[PeterDonis]

The infinity of the universe is just a conjecture, not a proven theory.

I have no idea what you think this has to do with my response to your previous statement.

This was an example of "Some other interpretation..."

We are discussing the MWI in this thread. If you want to discuss some other interpretation, you need to start a separate thread (and you need to base it on some kind of actual reference, not just an interpretation you made up yourself).