Re: [asa] The Multiverse - Physics or Metaphysics?

I'll reply to David on this one, but in the same post respond to a comment
of George's.

On 9/11/07, David Heddle <heddle@gmail.com> wrote:
>
> The worst part of the string landscape multiverse is that it means the
> death of physics in that it holds that the search for a fundamental theory
> is a fool's errand. Susskind even likens such a search to a religious
> endeavor, which is not intended as a compliment.
>

David,

Perhaps you can answer a question for me on this, as I'm not a real expert
on String theory so I might be talking nonsense.

Is it the case that the "string landscape" corresponds to a finite (but
large 10^500) set of solutions to the theoretical equations?

The reason for asking is that just because there may be many solutions to
the equations does not imply that all the alternate solutions actually exist
in reality (though it's not clear what "reality" means for alternate
universes which we can't see and can't interact with). We've all been
through the exercise where you solve a quadratic equation to get the
solution to an applied maths problem, and you churn through the (-b +/-
sqrt(b^2 -4ac))/2a formula, and then you choose one solution and
automatically discard the other one because it's obvious that it's
non-physical.

So what if it's the case that there is only 1 of the 10^500 solutions that
is "physical reality", and none of the others are? It seems to me that then
you are back with the fine tuning problem with a vengeance ( 1 chosen out of
10^500 ). And since none of the other supposed universes are detectable to
us, I don't see any way of deciding whether just 1 exists or whether all
10^500 exist.

Smolin can not take the high road, however. In spite of claims to the
> contrary, his explanation of the anthropic coincidences vis his theory of
> cosmic evolution:
>
> 1. Black holes beget new universes
> 2. The child universes will have similar (but not quite the same) physics
> 3. Therefore universes good at producing black holes will evolve via
> natural selection
> 4. coincidentally they, since they have stars and galaxies, are the same
> types of universes that can support life
>
> is not testable, beyond his challenge to imagine a universe that is much
> better at creating black holes. Plus he never satisfactorily justifies why
> the child universes should have "close to but not exactly the same" physics.
>

Put that way, Smolin's cosmic evolution does seem to be a highly speculative
theory, and furthermore, as you've described it, it runs into the same
"origin of life" problem that Koonin's paper tries to address. The theory
might work fine once you've got the first black hole. But how does the
first black hole come about? Its existence implies, surely that stars and
galaxies exist, which then collapse into black holes. In other words they
must come from universes that are already capable of supporting life?

In many ways it seems also to me that this is no different philosophically
than the multiverse.

The reason seems to me to be that the objections to Intelligent Design, the
Multiverse, and invoking coincidence all fail in the same way as far as
being scientific, in that they appeal to a universal explanatory mechanism -
any of them can explain absolutely anything, and therefore they explain
nothing. And once you've got this "explanation" from your universal
solution provider, there is nothing else you can do to understand it
further.

It seems to me that the same applies to just invoking "evolution" as the
explanation, without any further evidence. Now, in biological systems there
is plenty of evidence to support the fact that evolution has occurred, and
so it makes sense, when we come across some complex mechanisms, to look for
explanations within an evolutionary framework. But just to say "it must
have evolved" and not do anything more is really no more scientific than
saying "it was designed by an intelligent designer", or "it was an anthropic
coincidence that we happen to be in one of the universes in the multiverse
that got lucky".

At the end of the day, we MUST keep searching and try and understand things
better. We can't just say "it must have evolved" and give up the search for
HOW it evolved. But if, as you say, Smolin's ideas are untestable, then
that is about as far as you can go. With biological systems we can look at
fossil sequences, DNA sequences etc, and compare between species. But
clearly we can't compare the genomes of different universes.

When George said: "Those who regard natural selection as a kind of
universal solvent for traditional beliefs, & especially religion ..." that
also rang true with the way I'm thinking. Evolution without doing other
science is indeed potentially a universal solution provider. [George, I
don't know if you meant "solvent" in both senses of the word; ie something
which dissolves something away, AND something which is a solution ie
explanation to a problem. Hope I didn't misrepresent you by taking it both
ways].

Regards,
Iain

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Received on Tue Sep 11 13:24:58 2007