Federico Marulli writes:
> I am an Italian student of Cosmology and it is the first time I write
> something in this mailing list. I didn't have the time to read all your
> messages, so I don't know if my thought about multiverses is a new one or
> not. Anyway I would like to propose you my reflection about this topic.

Welcome to the list!

> My reasoning is rather simple. Dealing with an infinite level 1
> multiuniverse, if an event, even an improbable one, doesn't violate any
> pshysical laws, it necessarly has to happen infinite times and in infinite
> different points of the space.

I think your reasoning is valid, there will be observers who see various
physical laws being violated.  However I disagree with some of your

>  From all these examples we should deduce that, if all the infinite
> observers we have considered took advantage of the same approach we have,
> they would obtain very different interpretations. So the model seems to
> admit in itself the chance of being wrong. It is consistent with its
> foundamental hypotheses the fact that it is inconsistent. So here we have
> the paradox. But shall we put into discussion our experimental method just
> because some unlucky observers are not in the condition to understand the
> universe and the way it works?

What is the paradox here?  Are you saying that our deduction that we
live in a level 1 multiverse (i.e. one which is infinitely large and
full of stars and planets much like our own) is possibly wrong?  That may
be true but it doesn't strike me as a paradox.  All of our reasoning is
potentially wrong; we may be delusional, we may be misinterpreting our
results, we may be unlucky and atypical (for example, earthlike planets
may be enormously less likely than we imagine).  The possibility of
being wrong is fundamental to scientific and philosophical inquiry.  I
don't see that this new source of potential wrongness rises to the
level of a paradox.

>  At last we could object that all of this is admitted by our own model
> and, if this absurdity really happened, we should only notice that we live
> in a very improbable universe. But if it was true, it would be completely
> unuseful for us to keep our mathematics and physics. For instance, if we
> started, by chance, to obtain number 6 any time we throw a die, and if
> this would be like that till the end of time, it would be unuseful for us
> to go on considering the theory of probability as valid. There would be no
> sense for us to think of having 1/6 of chances to obtain number 6, seen
> that we would obtain it in any case.

The problem with this reasoning is that there are many more observers
who see the laws of physics violated only rarely than those who see them
violated continually.  Let's suppose that suddenly we start observing
a violation, like suddenly we get a 6 every time anyone throws a dice.
Now, looking forward, there are universes where that odd behavior
continues forever, and universes where that behavior stops and we go
back to the normal laws of probability.  The point is that the second
set of universes is overwhelmingly more numerous than the first.  (If you
are concerned about comparing infinite universes, consider looking at a
large but finite volume of the universe, as the volume goes to infinity.)

So in fact we would be correct at every point to expect the normal laws
of physics to resume, because enormously more copies of ourselves will
find that to happen than those who find the violations to continue.

Hal Finney

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