richard_dawkins_-_the_god_delusion
W 11 Y '1 11 !•; R I. A I VI () S T C F. R T A I N I. Y ! S NO (.1 O I) 141one of the intensely rare planets that has bridged all three gaps.Natural selection works because it is a cumulative one-waystreet to improvement. It needs some luck to get started, and the'billions of planets' anthropic principle grants it that luck. Maybe afew later gaps in the evolutionary story also need major infusionsof luck, with anthropic justification. But whatever else we may say,design certainly does not work as an explanation for life, becausedesign is ultimately not cumulative and it therefore raises biggerquestions than it answers - it takes us straight back along theUltimate 747 infinite regress.We live on a planet that is friendly to our kind of life, and wehave seen two reasons why this is so. One is that life has evolved toflourish in the conditions provided by the planet. This is because ofnatural selection. The other reason is the anthropic one. There arebillions of planets in the universe, and, however small the minorityof evolution-friendly planets may be, our planet necessarily has tobe one of them. Now it is time to take the anthropic principle backto an earlier stage, from biology back to cosmology.THE ANTHROPIC PRINCIPLE:COSMOLOGICAL VERSIONWe live not only on a friendly planet but also in a friendly universe.It follows from the fact of our existence that the laws of physicsmust be friendly enough to allow life to arise. It is no accident thatwhen we look at the night sky we see stars, for stars are a necessaryprerequisite for the existence of most of the chemical elements, andwithout chemistry there could be no life. Physicists have calculatedthat, if the laws and constants of physics had been even slightlydifferent, the universe would have developed in such a way that lifewould have been impossible. Different physicists put it in differentways, but the conclusion is always much the same. Martin Rees, inJust Six Numbers, lists six fundamental constants, which arebelieved to hold all around the universe. Each of these six numbersis finely tuned in the sense that, if it were slightly different, the
142 i i 1 1 t, O I) :> 1 [.universe would be comprehensively different and presumablyunfriendly to life.*An example of Rees's six numbers is the magnitude of the socalled'strong' force, the force that binds the components of anatomic nucleus: the nuclear force that has to be overcome when one'splits' the atom. It is measured as E, the proportion of the mass ofa hydrogen nucleus that is converted to energy when hydrogenfuses to form helium. The value of this number in our universe is0.00"7, and it looks as though it had to be very close to this value inorder for any chemistry (which is a prerequisite for life) to exist.Chemistry as we know it consists of the combination and recombinationof the ninety or so naturally occurring elements of theperiodic table. Hydrogen is the simplest and commonest of theelements. All the other elements in the universe are made ultimatelyfrom hydrogen by nuclear fusion. Nuclear fusion is a difficultprocess which occurs in the intensely hot conditions of the interiorsof stars (and in hydrogen bombs). Relatively small stars, such asour sun, can make only light elements such as helium, the secondlightest in the periodic table after hydrogen. It takes larger andhotter stars to develop the high temperatures needed to forge mostof the heavier elements, in a cascade of nuclear fusion processeswhose details were worked out by Fred Hoyle and two colleagues(an achievement for which, mysteriously, Hoyle was not given ashare of the Nobel Prize received by the others). These big starsmay explode as supernovas, scattering their materials, including theelements of the periodic table, in dust clouds. These dust cloudseventually condense to form new stars and planets, includingour own. This is why Earth is rich in elements over and above theubiquitous hydrogen: elements without which chemistry, and life,would be impossible.The relevant point here is that the value of the strong forcecrucially determines how far up the periodic table the nuclearfusion cascade goes. If the strong force were too small, say 0.006* 1 say 'presumably', partly because we don't know how different alien forms oflife might be, and partly because it is possible that we make a mistake if we consideronly the consequences of changing one constant at a time. Could there beother combinations of values of the six numbers which would turn out to befriendly to life, in ways that we do not discover if we consider them only one at atime? Nevertheless, I shall proceed, for simplicity, as though we really do have abig problem to explain in the apparent fine-tuning of the fundamental constants.
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W 11 Y '1 11 !•; R I. A I VI () S T C F. R T A I N I. Y ! S NO (.1 O I) 141
one of the intensely rare planets that has bridged all three gaps.
Natural selection works because it is a cumulative one-way
street to improvement. It needs some luck to get started, and the
'billions of planets' anthropic principle grants it that luck. Maybe a
few later gaps in the evolutionary story also need major infusions
of luck, with anthropic justification. But whatever else we may say,
design certainly does not work as an explanation for life, because
design is ultimately not cumulative and it therefore raises bigger
questions than it answers - it takes us straight back along the
Ultimate 747 infinite regress.
We live on a planet that is friendly to our kind of life, and we
have seen two reasons why this is so. One is that life has evolved to
flourish in the conditions provided by the planet. This is because of
natural selection. The other reason is the anthropic one. There are
billions of planets in the universe, and, however small the minority
of evolution-friendly planets may be, our planet necessarily has to
be one of them. Now it is time to take the anthropic principle back
to an earlier stage, from biology back to cosmology.
THE ANTHROPIC PRINCIPLE:
COSMOLOGICAL VERSION
We live not only on a friendly planet but also in a friendly universe.
It follows from the fact of our existence that the laws of physics
must be friendly enough to allow life to arise. It is no accident that
when we look at the night sky we see stars, for stars are a necessary
prerequisite for the existence of most of the chemical elements, and
without chemistry there could be no life. Physicists have calculated
that, if the laws and constants of physics had been even slightly
different, the universe would have developed in such a way that life
would have been impossible. Different physicists put it in different
ways, but the conclusion is always much the same. Martin Rees, in
Just Six Numbers, lists six fundamental constants, which are
believed to hold all around the universe. Each of these six numbers
is finely tuned in the sense that, if it were slightly different, the
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