Three Roads To Quantum Gravity

WHAT CHOOSES THE LAWS OF NATURE?
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If possibility 1 is true, then all we can do is take the story of
string theory as a cautionary tale. So let us put this one aside
and look at the others. If possibility 2 is true, then we are left
with a puzzle: what or who chose which consistent theory
applies to our world? Among the list of different possible
consistent theories, how was one chosen to apply to our
universe?
There seems to be only one possible answer to this
question. Something external to the universe made the
choice. If that's the way things turn out, then this is the
exact point at which science will become religion. Or, to put it
better, it will then be rational to use science as an argument
for religion. One already hears a lot about this in theological
circles, as well as from certain scientists, in the form of
arguments based on what we might call the anthropic
observation. It seems that the universe we live in is very
special. For a universe to exist for billions of years and
contain the ingredients for life, certain special conditions
must be satis®ed: the masses of the elementary particles and
the strengths of the fundamental forces must be tuned to
values very close to the ones actually we observe. If these
parameters are outside certain narrow limits, the universe
will be inhospitable to life. This raises a legitimate scienti®c
question: given that there seem to be more than one possible
consistent set of laws, why is it that the laws of nature are
such that the parameters fall within the narrow ranges needed
for life? We may call this the anthropic question.
If there are different possible consistent laws of nature, but
no framework which uni®es them, then there are only two
possible answers to the anthropic question. The ®rst is that
we are very lucky indeed. The second is that whatever entity
speci®ed the laws did so in order that there would be life. In
this case we have an argument for religion. This is of course a
version of an argument which is well known to theologians ±
the God of the Gaps argument. If science raises a question like
the anthropic question that cannot be answered in terms of
processes that obey the laws of nature, it becomes rational to
invoke an outside agency such as God. The scienti®c version
of this argument is called the strong anthropic principle.