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Comment by tim333 | Hacker News Reader

I'm not sure your explanation for the lack of spookiness in many worlds works. The essence of most Bell's Theorems experiments is you start with entangled photons (or similar), they travel a long way apart and then go through polarisers at either end and into detectors. The odd thing is that the number getting through both slits depends on the angle between the polarisers. But how does the photon at polariser 1 know what the orientation of polariser 2 is at the time it's pair photo gets there? You can spin the polariser and the chances of it getting through depends on the orientation when the photon gets there, not when it set off. You'd think it can't but experimentally it does. I don't see how that weirdness goes away with many worlds.

(Bell's theorem is basically maths to figure out if the photons have to 'know' the angle between the polarisers rather than just say start off with the same polarisation.)

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For as far as I can tell, the solution is that whenever there is a choice to be made, all choices are made and you get separate branches/parallell universe bubbles that expand at the speed of light, interacting (or not) with other universe bubbles. The bubble in which entangled electron A had spin up interacts with the other in which electron B had spin down and vice versa.

So essentially you have an ever growing set of merging and splitting history branches, always growing for every point in space, continously.

I've got no idea how to make that work for your example of polarizers, or for the example of delayed quantum eraser experiments, etc... The surface of the bubbles apparantly have to carry all of that information and there must be some mechanism for them to decide which ones interact with which others.

They aren't exactly bubbles expanding at the speed of light (necessarily). They are more like: when you get a particle interaction whose outcome is determined by a fact which has more than one answer, you get more than one outcome. And that applies recursively as those particles whizz off and interact with anything else.

It's possible though unlikely that they could be expanding no faster than the speed of a walking scientist - if nothing else in the universe is yet causally determined by the outcome.

How does this not enable ftl information transmission?

It seems to me that you have a valve that instantly opens/close a different valve at an arbitrary distance.

You can't control what the value will be or when it will open/close. It isn't a detectable "push event" like in computer systems.

Because whether the spin is up or down when you observe it is completely random. Both observers at either end would believe they looked at it first without any other information, and the stream of bits would be completely random AND 100% correlated with other.

Ok, so you will always have perfect correlation and since you spun the polarizer after the photons started moving that implies spooky action at a distance.

right?

Many worlds makes it clear how it can't: because there is no FTL transmission. There is only stuff that has been pulled into the superposition (seeing a definite answer) and stuff that hasn't yet (for which both answers are still superposed). When the latter comes in contact with the former, it enters the superposition, which from the outside perspective is a split. From the inside perspective, it looks like "the superposition collapsed". From the outside, one side gets "open" and the other gets "closed". From the inside, this looks like getting a random answer.

You can see intuitively why this can't convey information. You always get both answers (in different "worlds").

That doesn't really explain the mechanics of the splitting process.

It's "And to explain this, we postulate that a whole new universe appears fully formed out of nowhere, with an identical history but a distinguishable future, because it does."

I suppose it's possible. But it doesn't seem very parsimonious - because you effectively have to double the energy in the multiverse for every distinguishable quantum event.

Does conservation of energy not apply in the multiverse? Are universes - as many as you need - free at point of sale?

Splitting is just a metaphor for a superposition of macroscopic states. There's no extra mechanics involved.

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