Re: Possible Worlds, Logic, and MWI

From: Tim May <tcmay.domain.name.hidden>
Date: Fri, 10 Jan 2003 20:54:38 -0800

On Friday, January 10, 2003, at 05:21 PM, Hal Finney wrote:
> Conventional decision theory is designed to handle exactly this sort
> of situation. According to those principles, you would act to maximize
> your expected utility. Since you get more utility from an apple than
> from an orange, and the coin flip has a 50-50 chance of coming up
> heads or tails, your expected utility is maximized by specifying that
> you will get an apple whether the coin falls heads or tails. This is
> very obvious even without being expressed in the mathematical form that
> decision theory uses.
>
> Wei suggested that in the context of a many-worlds universe (not just
> the quantum MWI but even for a broader set of possibilities), you might
> not make this same decision. You know that when the coin flips, the
> universe is going to effectively branch and both possibilities are
> going
> to be actualized. Let us suppose that in addition to slightly
> preferring
> apples to oranges, you have a strong value preference for diversity.
> You like variety and you dislike having everything the same everywhere.
> In that case, you might rationally choose to receive an apple on heads
> but an orange on tails. While this slightly reduces your average
> pleasure level in terms of tasting the fruit, this could be more than
> compensated by your increased pleasure at knowing that you are enjoying
> diverse experiences in the two worlds.

Accepting that I believe in the MWI (_really_ believe, not just believe
in the formalism), I already know that all possible decisions, all
diverse forks, are already unfolding in the multitude of forking paths.
Even if I "decide" not to alter my rational choice for the fruit, there
are countless other mes making every other possible choice, including
10^50 or more mes who wire up the coin toss to explode an H-bomb "just
to make things interesting in that sheaf of branches."

(The awkward word "mes" is the plural of "me." )

But in this, the only universe I will ever, ever have contact with, I
optimize as best I can. And I assume all the myriad mes are doing the
same in their universes, forever disconnected from mine.

Someone here on this list asked me in private mail if I didn't take
some amount of comfort from the MWI, knowing that versions of me were
surviving and thriving in other branches regardless of what happened to
me in this branch.

No, I told him, while there may "be" other such paths (and I can argue
there already are, via modal logic, without any quantum mechanics
involved), these other paths are unreachable to me and may as well not
exist at all.

Nor do I find despair in the notion that there may be (_are_, if MWI is
right) other universes in which I am a mass murder, in which I killed
myself 12 years ago, in which the Earth was hit by a comet two
centuries ago, in which a plague will be released next year and will
wipe out all humans.

Until some evidence of cross-path communication or travel or
interaction is found, the MWI gives the expected result, that I am in
this world and no others, for all intents and purposes.

By the way, I don't dispute at all that having a belief in MWI might
very well cause behavior changes, even the change you and Wei have
given as an example. Besides this change, of picking a less desirable
fruit in your example so as to "increase diversity," I can imagine that
some people who strongly believe in MWI may take _fewer_ risks (to
maximize the number of their surviving dopplegangers in other
branches), may take _more_ risks, may do things of various kinds which
they think will somehow influence or be influenced by the reality of
MWI.

But the same may be said of beliefs of all sorts, including beliefs in
an afterlife (fewer risks, more risks, fatalism, etc.), beliefs in
cryonics, beliefs in the I Ching or magic, and so on. Most religious
people behave quite a bit differently than I do. The Muslims who
believe their martyrdom will bring them infinite reward in an afterlife
are but the most obvious examples of how belief alters behavior.

A strong belief in the MWI, at a basic level, would probably be
sufficiently strong to alter psychological states in various ways. The
hard part is finding any real rational argument for what those
alterations might be.

As it now stands, I will not be standing in front of any machine guns
to test the MWI, nor will I be choosing different stocks to invest in
so as to support "multidiversity." For all intents and purposes, this
is the world I am in.

I'll be interested to see if any more compelling examples can be
produced.

A brief comment:

>
> So here is an example where belief in multiple worlds could lead a
> rational person to behave differently than belief in a single world.
> For this effect to occur, I think our preferences in the many-worlds
> case have to depend on relations between the worlds, rather than
> independently on conditions in each world. We're not just acting to
> maximize the expected outcome in each world averaged across all of
> them,
> we're acting to maximize the utility of the "big picture", the entire
> set of worlds affected by our acts, considered as a whole.

Why would there be any reason to try to maximize the utility of this
"big picture"?

For those of us who don't even strive for "the greatest good for the
greatest number" in a single-branch universe, why would striving for
more good (whatever "good" is) in 10^300+ branches be interesting or
important?

In any case, if MWI is correct, then there is every type of universe
imaginable, consistent only with the laws of physics and math, and
every decision for the good or the bad or whatever has been made
countless times in countless ways. By any calculus of the multiverse,
the sheaf of universes in which Tim May or Hal Finney even exist is of
measure approaching zero.

Meanwhile, I'm _here_.

--Tim May
"Dogs can't conceive of a group of cats without an alpha cat." --David
Honig, on the Cypherpunks list, 2001-11
Received on Fri Jan 10 2003 - 23:57:05 PST