Re: Strange Anthropic Probabilities

From: Hal Finney <hal.domain.name.hidden>
Date: Sun, 11 Jan 2004 17:12:22 -0800

Doug Porpora writes:
> Let me also say I find it a morally ghastly proposition that each of
> us is duplicated an infinite number of times in an infinite number of
> universes. If so, why ever bother to do the right thing? Some
> infinite set of me's will be doing the wrong thing, so why not be one
> of them?

I'll offer some thoughts on this below.

> So I have been thinking of possible counter considerations. Here is
> one: Is it possible that the parametric coincidences required for
> the existence of advanced (beyond microbial) life are so improbable
> that (i) even in the right kind of universe, advanced life is likely
> to occur only once; and (ii) it requires an infinite number of
> universes even to get one occurrence of a me-ish person?

That would require that it is infinitely improbable that you could exist.
But I don't think that is the case, because there are only a finite
number of possible arrangements of matter of the size of a human being.
(Equivalently, humans embody only a finite amount of information.)
So it would seem that the probability of a human appearing in some
universe must be finite and greater than zero, hence there would be an
infinite number of instances across an infinity of universes.

As far as the issue of human action and free will, here is how I look
at it. There are really two issues. The first is that in some sense
the multiverse makes our actions deterministic. That is, there is no
longer any true unpredictability in what we do, because we do everything
in one universe or another. So how can we have free will if there are
no choices?

Well, this problem has been considered many times in the philosophical
literature going back hundreds of years (where it was asked how free will
was compatible with God's omniscience). Recent works by Daniel Dennett,
his books Elbow Room and his new book (which I haven't read) Freedom
Evolves, discuss how free will can be said to coexist with determinism.
The basic idea is that the acting out of deterministic processes and the
considerations involved in making a free choice are two equally valid ways
of explaining the same phenomenon, at different levels of description.
These books could be good sources to explore these concepts further.

The second part of the problem is specific to the multiverse model,
which is, even assuming that in some sense you have free will, what is
the practical point of acting, since your decisions will be in effect
cancelled out by being done differently in other universes? Larry Niven's
science fiction short story All the Myriad Ways explores the problems
which sweep society when a technology is invented to visit parallel
universes, leading to a widespread surrender to nihilism and social ennui.

However this perspective ignores the concept of measure, where some
universes are more prominent than others. Although you may make
different choices in different universes, the probabilities are not equal.
Your decision making processes influence the measure of the universes in
which your different choices occur. By giving matters careful thought
and making wise decisions, you can maximize the measure of the universes
in which your choices have good outcomes. This justifies the necessity
of careful choice and eliminates the descent into nihilistic horror
and despair.

Hal Finney
Received on Sun Jan 11 2004 - 20:14:12 PST