ethan@utastro.UUCP (Ethan Vishniac) (10/09/84)
[In the beginning was the bug]
The arguments in this group have included discussions
of why we cannot assign a probability to abiogenesis, and
some mention of the meaninglessness of discussing the
probability of a single event. What people have not stressed
sufficiently is that in addition to those two problems it is
also true that we do not know the size of the sample of which
Earth is a part.
Suppose for a moment that the probability of abiogenesis
occuring on a suitable planet within 10^10 years is 10^60
(the second number is chosen for the sake of the argument, the
first number is a rough estimate of the age of the universe).
We don't know the probability of forming suitable planets, but
we can assume it is of order unity. It probably is not orders
of magnitude below that. There are approximately 10^11 stars
in our galaxy. The number of galaxies within the *observable*
universe is on the order of 10^11. This gives us 10^22 stellar
systems where life could have formed. However, we are not done.
We have no firm idea of how large the universe is, or to be
more precise that part of the universe that is like the part we
live in. However, we can be fairly certain, based on the homogeneity
of the microwave background, that it is *much* larger than what we
observe. That being the case, we have no way of assigning a
probability to life evolving naturally *somewhere* in the universe.
If the universe is sufficiently large then that probability will
approach unity regardless of how small it is for any particular
planet.
Now, I have a question for the creationists out there.
The natural origin of life (abiogenesis) on a primitive Earth is a
hypothetical event which is neither well understood nor forbidden
under the laws of nature. Creationists in this discussion group
have spent a large amount of time trying (unsuccessfully in my opinion)
to show that such an event is impossible. Suppose they are right.
What does this show? That life came from elsewhere either accidentally
or through the purposeful intervention of some higher power (which
is not necessarily supernatural). How is this relevant to the question
of the evolution of life on Earth?
"I can't help it if my Ethan Vishniac
knee jerks" {charm,ut-sally,ut-ngp,noao}!utastro!ethan
Department of Astronomy
University of Texas
Austin, Texas 78712