Atheism and Theism 19values of the fundamental constants randomly distributed between them, then
it could be virtually certain that some universes would be such that galaxies,
stars, planets, life and intelligence evolved within them. The anthropic prin-
ciple allays surprise that we are in such a universe. Obviously as intelligent
beings we must be in a universe that allows intelligence to arise. This explana-
tion, depending as it does on the many universes hypothesis, does not have the
back to front character of the example that we have recently been discussing.
But how good is the world ensemble explanation?
An unattractive feature of the explanation is its apparent prodigality. We
may be reminded of Ockham’s razor, the principle that entities should not be
multiplied beyond necessity. ‘Necessity’ is a bit strong: let us say, ‘without
more than compensating explanatory advantage’. Ontological parsimony must
be balanced against explanatory power. If Carter’s hypothesis really does explain
the fine tuning of our universe, then perhaps it should be accepted. Simplicity
and symmetry are features which make for a good explanatory theory or hypo-
thesis. Now the random distribution of relations between the fundamental
constants in the various universes which belong to the huge ensemble of
universes restores a symmetry that is missing in our ordinary ‘one universe’
theory, with its antecedently improbable set of relations between the funda-
mental constants. A random distribution of the fundamental constants of nature
presumably requires no explanation in the way that a particular and arbitrary
looking set of such values would. There is a sort of symmetry in randomness.
John Leslie has told a ‘firing squad’ story that illustrates Carter’s point.^31
Suppose that you are put for execution before a firing squad and to your
surprise all the members of the squad, good shots though they are, all miss.
You would be extremely surprised to be still alive. Suppose, however, that you
knew that there were a billion people like you being executed by firing squad;
you might calculate that it was quite probable that there would be a few lucky
survivors, and so you must be one of them. You should feel surprised and
fortunate, but there would not be the sort of puzzlement that you might feel
if you had been the only candidate for execution. You would feel only the sort
of surprise that the winner of a lottery might feel. In a practically possible
case, of course, there could not be a billion other similar firing squads and
victims and you would guess that the firing squad had some reason not to kill
you, and this would be a sort of analogue of the design (theistic) explanation
of the fine tuning. Leslie’s considerations, however, do support the view that
Carter’s multiple universes hypothesis, or something very like it, could pro-
vide a non-theistic explanation of the fine tuning of our universe, as a serious
rival to the theistic design explanation. If our universe were not one of the
tiny proportion of fine tuned ones we would not be here to tell the tale.
Similarly, if the man is missed by the firing squad he reflects that of course he
must be one of the few to survive.