On Friday, January 10, 2003, at 05:21 PM, Hal Finney wrote:
Conventional decision theory is designed to handle exactly this sortAccepting 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."
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.
(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:
Why would there be any reason to try to maximize the utility of this "big picture"?
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.
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_.
"Dogs can't conceive of a group of cats without an alpha cat." --David Honig, on the Cypherpunks list, 2001-11