[extropy-chat] Is Many Worlds testable?

[John K Clark]

"scerir" <scerir at libero.it>

> in Copenhagen a quantum state is more 'available information' (hence the
> collapse) than physical entity. On the contrary, in MWI it is a physical
> entity.

If there are 2 competing theories and one deals more with physical entities
than the other I would say it is the superior theory; the name of the
science after all is "physics".  Abstraction for abstraction's sake just
does not thrill me.

> From the 'Everett faq' I get (if I understand what I read) that
> measurement causes the 'split'

Well, from the faq you included in your post I read "The wavefunction obeys
the empirically derived standard linear deterministic wave equations at all
times. The observer plays no special role in the theory and, consequently,
there is no collapse of the wavefunction." That sure doesn't sound to me
like that supports your position.

To be fair it also says "each measurement causes a decomposition or
decoherence of the universal wavefunction into non-interacting and mostly
non-interfering branches, histories or worlds." How do I explain that?
As I said before when you make a measurement the important thing is
not that you now have a record of some sort, the important thing is that
you changed something. You can replace that super sophisticated,
hyper expensive, extraordinarily wonderful, photographic film with a
wall made of donkey dung, and it will make no difference, both will
stop a photon and cause a universe to split.

> So, according to deWitt, it is more a _coupling_ than a measurement.

Exactly. A photon's quantum properties are coupled to a wall of donkey dung
in one universe and not coupled to a wall of donkey dung in another; so the
universes split.

> it seems to me that MWI (not to mention Copenhagen!) does not tell us what
> happens between times t1 and t2

Please name the observation you have recorded during that interval that
Copenhagen can explain but Many Worlds cannot.

> Another problem I have is the one-slit diffraction
(different from the two-slit interference)

Things are indeed a bit more complex when dealing with diffraction rather
that interference, and if Copenhagen can explain what is going on more
clearly than Many Worlds then I have lost the argument. But can it? One
theory must explain the complex dynamics between one universe and another;
the other theory must explain the complex dynamics between what is real and
what is not. I'm not a gambler and I could be wrong, but I know where I'd
put my money.

Best regards. And I want you to know I'm really enjoying this debate;
regardless if I end up winning or losing I want you to know I think you are
a fine fellow.

John K Clark