[extropy-chat] Role of MWI and Time Travel

[Lee Corbin]

Serafino writes

> Lee Corbin:
> > Remember that QM under MWI is a completely 
> > deterministic theory, and that "free will" 
> > is an awkward concept in deterministic systems.

Uh, I have already retracted that as written, as it gives
the erroneous impression that in non-deterministic systems
"free will" would not be awkward. The truth is that free
will, while it makes sense when appropriately defined by
people who renounce any concept of soul, is otherwise
very "murky", as Douglas Hofstadter used to say.

> # I may be wrong - since I don't like Everett's
> theory, and MWI, and Many Minds, and even the 
> Relational theories by Rovelli, Mermin, etc. - 
> but MWI is a deterministic theory in a very specific 
> sense.

Yes---that is exactly what the adherents of MWI believe
(e.g. it's stated many places in Deutsch's book).

> One can say that the quantum states of QM evolve 
> deterministically in time. One can say that Everett's
> or MWI Universal Wavefunction evolves deterministically
> in time.

Yes.

> (There are hints, though, that even this statement
> is somehow simplistic, since there are strange cases, 
> pointed out, i.e., by David Z. Albert [1]).  

That I didn't know, thanks.

> But that has nothing to do with the definiteness
> of the predicted outcome of the possible measurement
> performable on a specific system while it is in a given 
> prepared state.

Yes, but your case of a specific system in a given prepared
state is not the general case. In the general case, it's
not possible, as you know, to announce ahead of time which
Everett branch you'll be in, at least in the sense of being
able to win bets. (You can always say that you'll be in 
both or all branches.)

> Even within MWI one cannot predict, in a deterministic
> way, the definite outcome of the possible measurement
> performable on a specific system

A way in which it is "sort of" possible to predict the
definite outcome is to predict the probabilities of the
outcomes; then, in MWI, one assumes that the branches
split deterministically according to the prescribed
probabilities.

> Russell Wallace:
> > Physics _has nothing whatsoever to do with free will_. 

The nit I can pick with Russell's statement is this. If
we take "physics" to mean "the basic rules of the world",
then physics has everything to do with free will: what if,
for example, physics were to include spiritual phenomena
so that souls exist which may make uncaused decisions?
Then free will would exist in the everyday meaning of the
term.

> # I don't know if physics has something to do with
> human free will. The problem seems to be the free will 
> of simple systems [2], which is more subtle, since the
> Bell - Kochen & Specker theorems [3] aborted the so 
> called 'value definiteness' of quantum states. 

The key question then comes down to what is meant, again,
by "free will". I studied Conway's idea, and even attended
a lecture he gave. But I can't say I understand exactly
what he's driving at.  Russell gave as good a definition
as I've ever seen:

    Free will is defined as the state of affairs
    where the causal matrix that determines the
    outcome includes your mind as a significant
    part.

Where, by the way, "mind" means the program that is being run
on one's brain.

Lee