many verses



The main motivation of no-collapse interpretations is to emphasize that the unitary Schroedinger evolution is all there is.



In order to reconcile this with our experience a description considering 'many worlds' or 'many minds' and the 'splitting' of the universe into different 'branches' is often used:
The physicist does not kill the cat but really creates two worlds and then repeating this experiment doubles the number again and again.

It seems that the number N of 'branches' or different 'minds' etc. increases like N(t) ~ wt where w is some unknown constant. Now one can calculate something like an entropy S from it as S = log(N) and therefore S ~ t; time really is 'm.w.i entropy'.



But how does one reconcile all this with the time-reversible Schroedinger evolution?


13 comments:

Anonymous said...

Could you elaborate a little? Not sure I understood properly

wolfgang said...

Well, to repeat the idea in different words:
The unitary Schroedinger evolution does not 'prefer' the future over the past, it has no time arrow built in.
But the picture of the 'branching worlds', as usually used in many worlds interpretations, seems to have such an arrow with many branches in the future and less in the past.
This seems to be a problem to me.
How do you get the clean initial state (only one branch) if you evolve the wavefunction backwards in time?

Anonymous said...

Have you ever brought this issue up to any proponent of the MWI?
If you have, what did they reply?

wolfgang said...

The physicists I know personally are not too interested in this kind of problem (at least I am not aware) - so there was no opportunity yet for me to directly ask this question to a mwi proponent.

Anonymous said...

Ok, does it apply equally to the approach proposed by Wallace ?
I think those worlds sort of "emerge" rather than the "strong splitting" by Dewitt

wolfgang said...

I know that David Wallace tried to derive the Born rule using decision theory. A discussion of this issue is e.g. here.

I am not familiar with his particular proposal that the many worlds "emerge".
Do you have a link or reference?

Anonymous said...

http://users.ox.ac.uk/~mert0130/papers/handbook.pdf

There you go

Which MWI is it you are critizing?

wolfgang said...

Thank you for the link.
I don't think that this is different from e.g. deWitt mwi except for mentioning decoherence.
So I guess the question applies as well...

Anonymous said...

Decoherence is what the entire modern MWI is built on.
It's the decoherence which "splits" the worlds.

wolfgang said...

... and it seems that decoherence (if understood as branching of worlds) comes with an arrow of time and I would like to understand where it comes from.

Anonymous said...

I understand, but why don't you raise this issue to Wallace himself?
I doubt he would mind answering, and if he doesn't have an answer that's a answer in it self.

Maybe if you got other objections too you should include all of them in a mail and send it to him and see how he fares against them

wolfgang said...

maybe I should, but I assume that he is busy even without receiving email from cold-callers.

Anonymous said...

I doubt he's too busy to answer some genuine questions regarding a controversial interpretation which he adhere to..

Alternatively you could try to raise these issues over at physicsforums.com and see how the proponents respond there, thers a couple of PhDs there