Atheism and Theism 67which go as follows. An irregular bit of a larger molecular cloud broke off in
such a way that it took a special form and was rotating about its centre. This
irregularity allows an escape from the problem of the distribution of angular
momentum between planets and the sun which beset La Place’s nebular
hypothesis and its descendants. The dust grains accreted gravitationally into
planetesimals and these into planets, the whole process involving collisions
between the various bodies. Collisions indeed form an important part of the
story, and account for many of the varying characteristics (such as differing
inclinations to the ecliptic plane of the various planets). A large planet-sized
object is supposed to have collided with the earth. The resulting splash of
molten material formed the Moon, about 80 per cent of whose mass comes
from material from the impacting body, so that the Moon’s constitution is
dissimilar to that of the earth. The impacting body was destroyed in the
collision and the collision stripped away the early atmosphere, which eventu-
ally was replaced (through gas emanating volcanically from the earth) by an
atmosphere suitable for the evolution of life. This collision was a lucky accid-
ent for the prospect of life. Another lucky accident is that of the formation
of the huge planet Jupiter in its position outside the asteroid belt, since it
forms a gravitational barrier to comets. Without Jupiter perhaps a thousand
times as many would impact on the earth making conditions for life very
difficult.
The main matter of interest is how the formation of the solar system
depended on a lot of accidents, and how uniformitarian theories of its origin
are out of place. All the planets are importantly different from one another.
So even if there are many such systems in the galaxy, few might be suitable
for life and still fewer would develop intelligent life. Indeed Taylor is of the
opinion that we are alone in the universe.^108 Remember that we need not only
to multiply together all the probabilities of lucky astronomical accidents which
led to our solar system containing a planet suitable for life, but we have to
multiply this very small probability with the probabilities of all the lucky
biological accidents in the biological evolutionary process. We then need to
compare the reciprocal of this very small number with the huge number
of stars like our sun in the galaxy, multiplied again by the huge number of
galaxies. It is obviously very hard to estimate the probabilities and the final
answer.
Before I heard a lecture by Ross Taylor and read his book I was of the
fairly conventional opinion put forward by astronomers that there are prob-
ably hundreds of millions of planets with planetary systems suitable for the
evolution of life and that we are far from being the only intelligent beings in
our galaxy, let alone in the universe, and that probably there are vast numbers
of planets with intelligent beings technologically far in advance of ourselves.
At any rate Ross Taylor’s considerations suggest that although planetary