Hal, I follow your line of thought. It makes sense.

Intelligent life is very complex. So making it more prevalent in a universe
would mean adding complexity to that universe, thereby reducing its measure.

Still, one could apply a doomsday-like argument to say that if conditions
for intelligent life are so hard to get right, intelligent life should
arrive at a fairly late stage in the evolution of the universe, like late in
the stelliferous era. That does not appear to be the case in current
cosmologies, so perhaps a universe's likelihood should depend on more than
just ability to support intelligent life or simplicity.

----- Original Message -----
From: "Hal Finney" <[EMAIL PROTECTED]>
Sent: Sunday, January 11, 2004 9:57 AM
Subject: Re: Peculiarities of our universe

> There has been a huge amount written about the Fermi Paradox (why are
> there no aliens) over the years, and I don't want to reiterate that here.
> You can come up with scenarios in which intelligent life is common but
> where they just aren't visible, but IMO such explanations are not very
> natural.  Instead I propose that for the purpose of our discussion here,
> we accept the apparent fact that there are no other intelligent life
> forms within the visible universe.  Then let us consider the implications
> with regard to the All Universe Hypothesis (AUH), which says that all
> universes exist.
> This observation points to the fact that with our laws of physics,
> the evolution of intelligent life is extremely unlikely.  The question
> is, why?  Not, why do our laws of physics make it hard for life to form,
> but why do we live in a universe whose laws of physics have this property?
> Presumably, there are universes whose laws make life essentially
> impossible.  For example, they may be completely static, or equally bad,
> utterly chaotic.  But on the other extreme, there must exist universes
> where intelligent life is common.  At a minimum, we could create a such
> a universe in an ad hoc way by letting it be born full of intelligent
> life via forced initial conditions.  And probably there are other laws
> of physics which would be much more congenial for the formation and
> sustenance of intelligent life than our own.
> So we have some universes which are full of life, others which are devoid
> of life, and others where there is a chance for life to form but it is
> relatively small.  We appear to live in the third class.
> We talk about measure with regard to universes, and however it is defined,
> it seems that some such principle is needed to allow some universes
> to be more probable than others.  Otherwise we have our flying rabbit
> paradox where the universe could suddenly stop being lawful, or could
> have arbitrary exceptions to lawfulness.  Since there are more ways for
> things to go wrong than to go right, these exception-full universes would
> superficially be more numerous than those where the laws are universal.
> So there must be some property of the universal-law universes which makes
> it more probable for us to experience them than the others, and this is
> basically what we mean by measure.  Universes with more measure somehow
> play a larger role in the multiverse and we are more likely to live in
> one of them.  If universes with more consistent and uniform laws have
> greater measure, then this explains why we don't see exceptions like
> flying rabbits.
> However, it seems that the measure of a universe is not the only factor
> which should determine how likely it is to be observed; but in addition
> there should be a factor related to how many observers there are.
> The obvious case is for high-measure universes where observers are
> impossible.  No one will observe such universes.  This is the basic
> anthropic principle.  But I would extend this principle to say that the
> probability of observing a universe is proportional to the product of
> its intrinsic measure and some factor relating to the number of observers
> in that universe.
> There are a few different ways this factor might work.  The simplest would
> be to count the number of observers.  A universe with similar measure
> but twice as many observers would be twice as likely to be experienced.
> Another possibility would be to use observer-moments.  If two universes
> had the same number of observers, but in one they lived for twice as
> long as the other, then perhaps the second one would be twice as likely
> to be observed.  Yet another alternative would be to base the factor
> on the fraction of the universe's total resources incorporated into
> observers, rather than just the number of observers.  This would give a
> bonus to universes which were relatively efficient at creating observers,
> compared to universes which gained large numbers of observers merely be
> being inordinately large.
> The question of why we live in a sparsely populated universe, then,
> comes down to a comparison between the measure of a typical universe
> with many observers versus the measure of a typical universe with few.
> The former universes would get a large bonus factor for their many
> observers, while universes like ours don't have that.  So for our
> observations to be consistent with the AUH, it must be that universes
> like ours have much larger intrinsic measure than universes with many
> observers.  And since, as far as we can tell, our universe is not
> just sparsely populated, but extremely so, the measure differential
> in these two classes of universes must be extremely large.  That is
> (turning to the Schmidhuber interpretation) it must be much simpler
> to write a program that just barely allows for the possibility of life
> than to write one which makes it easy.  This is a prediction of the AUH,
> and evidence against it would be evidence against the AUH.
> On the face of it, this prediction doesn't seem too plausible to me.
> Of course, no one has ever written a program which evolves intelligent
> life, so we don't really know.  But our initial explorations towards
> artificial life seem to indicate that it's not particularly difficult
> to achieve model universes just swarming with tiny and unintelligent
> replicators.  Whether they could take the additional steps to become
> fully-fledged observers is an open question, one to which I suppose the
> AUH would have to predict the answer is no.
> Hal Finney

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