richard_dawkins_-_the_god_delusion

136 T II E G O O I) E I. U S I G N
zone at all, even at its closest approach to the sun, which it reaches
once every 560 Earth years. The temperature of Halley's Comet
varies between about 47°C at perihelion and minus 270°C at
aphelion. Earth's orbit, like those of all the planets, is technically an
ellipse (it is closest to the sun in January and furthest away in
July*); but a circle is a special case of an ellipse, and Earth's orbit
is so close to circular that it never strays out of the Goldilocks zone.
Earth's situation in the solar system is propitious in other ways that
singled it out for the evolution of life. The massive gravitational
vacuum cleaner of Jupiter is well placed to intercept asteroids that
might otherwise threaten us with lethal collision. Earth's single
relatively large moon serves to stabilize our axis of rotation, 68 and
helps to foster life in various other ways. Our sun is unusual in not
being a binary, locked in mutual orbit with a companion star. It is
possible for binary stars to have planets, but their orbits are likely
to be too chaotically variable to encourage the evolution of life.
Two main explanations have been offered for our planet's
peculiar friendliness to life. The design theory says that God made
the world, placed it in the Goldilocks zone, and deliberately set up
all the details for our benefit. The anthropic approach is very
different, and it has a faintly Darwinian feel. The great majority of
planets in the universe are not in the Goldilocks zones of their
respective stars, and not suitable for life. None of that majority
has life. However small the minority of planets with just the right
conditions for life may be, we necessarily have to be on one of that
minority, because here we are thinking about it.
It is a strange fact, incidentally, that religious apologists love the
anthropic principle. For some reason that makes no sense at all,
they think it supports their case. Precisely the opposite is true. The
anthropic principle, like natural selection, is an alternative to
the design hypothesis. It provides a rational, design-free explanation
for the fact that we find ourselves in a situation propitious to
our existence. I think the confusion arises in the religious mind
because the anthropic principle is only ever mentioned in the
context of the problem that it solves, namely the fact that we live in
a life-friendly place. What the religious mind then fails to grasp is
that two candidate solutions are offered to the problem. God is one.
The anthropic principle is the other. They are alternatives.
* If you find that surprising, you may be suffering from northern hemisphere
chauvinism, as described on page 115.