doesn't settle the matter for me to say that we cannot see the hand of a
designer in what we know about the fundamental principles of science. It might be that, although these principles
do not refer explicitly to life, much less human life, they are nevertheless
craftily designed to bring it about.
Some physicists have argued
that certain constants of nature have values that seem to have been
mysteriously fine-tuned to just the values that allow for the possibility of
life, in a way that could only be explained by the intervention of a designer
with some special concern for life. I
am not impressed with these supposed instances of fine-tuning. For instance, one of the most frequently quoted
examples of fine-tuning has to do with the energy of a certain excited state of
the carbon nucleus. The build-up in
stars of elements necessary for life, like carbon and oxygen, depends on the
carbon nucleus having an excited state at an energy within a narrow range,
where in fact just such a state is found.
The reason that it has to have this energy is to provide a way for
carbon nuclei be formed in stars in collisions of helium nuclei with unstable
beryllium nuclei, which is a necessary step in the build-up of all elements
heavier than helium. But recent
calculations show that, as has been long expected, without any fine tuning of
the constants of nature one would in any case expect the carbon nucleus to have
a state like an unstable molecule, consisting of a helium nucleus and a
beryllium nucleus, which would naturally have an energy close to the values
necessary for the synthesis of carbon and heavier elements.
There is one constant whose value does seem remarkably well adjusted in
our favor. It is the energy density of
empty space, also known as the cosmological constant. It could have any value, but from first principles one would
guess that this constant should be very large - much too large to allow matter
to clump together in the early universe, which is the first step in forming
galaxies and stars and planets and people.
It's too early to tell if this is a real problem, or if there is some
fundamental principle that explains why the cosmological constant must be this
if there is no such principle, recent developments in cosmology offer the
possibility of an explanation why the measured values of the cosmological
constant and other physical constants are favorable for the appearance of
intelligent life. Sidney Coleman has
shown how quantum mechanical effects can lead to a picture of the wave function
of the universe in which the wave function is the sum of many different terms,
each term corresponding to a big (or little) bang in which what we call the
constants of nature take all possible values.
Also, as you have heard here from Alan Guth, in the `chaotic inflation'
theories of Andre Linde and others our big bang is supposed to be just one
episode in a much larger universe in which big bangs go off all the time, each
with different values of the fundamental constants.
such picture, in which the universe contains many parts with different values
for what we call the constants of nature, there would be no difficulty in
understanding why these constants take values favorable to intelligent
life. There would be a vast number of
big bangs in which the constants of nature take values unfavorable for life,
and much fewer where life is possible.
You don't have to invoke a benevolent designer to explain why we are in
one of the parts of the universe where life is possible. In all the other parts of the universe there
is no one to raise the question.
conclude that the constants of nature have been fine-tuned by a benevolent
designer is like saying Isn't it wonderful that God put us here on earth,
where there's water and air and the surface gravity and temperature are so
comfortable, rather than some horrid place, like Mercury or Pluto. Where else in the solar system but on
earth could we have evolved?
like this is called anthropic.
Sometimes it just amounts to an assertion that the laws of nature are
what they are so that we can exist, without further explanation. This seems to me to be little more than
mystical mumbo-jumbo. On the other
hand, if there really is a large number of worlds in which some constant takes
different values, then the anthropic explanation of why in our world it takes
values favorable for life is just common sense, like explaining why we live on
the earth rather than Mercury or Pluto.
The actual value of the cosmological constant, recently measured by
observations of the motion of distant supernovas, is about what you would
expect from this sort of argument; it is just about small enough to prevent it
from interfering with the formation of galaxies and so on. But we don't yet know enough about physics
to tell whether there are different parts of the universe in which what are
usually called the constants of physics really do take different values. This is not a hopeless question; we will be
able to answer it when we know more about the quantum theory of gravitation
than we do now.
Contributed by: Dr. Steven Weinberg