Steinhardt and Turok present evidence that the cyclic theory matches all the current astronomical
observations with the same accuracy as the modified big bang theory, and show how it potentially can
explain and unify some aspects of the universe beyond the range of the big bang theory. No one yet
knows whether the cyclic universe theory will become an accepted part of astrophysics, in part
because it has been difficult to perform experiments to provide evidence that would support the
acceptance of string theory, which the cyclic theory presupposes. Nevertheless, I mention the cyclic
model here because it shows the possibility of an evidence-based answer to the question of why there
is something and not nothing. According to the model, there has always been something, namely,
branes, which are the historical causes of the existence of an infinite number of universes, including
ours. The main explanation of the existence of familiar things such as the sun, the planets, and
members of our own species is the big bang history of our universe, which originated through the
brane mechanism that Steinhardt and Turok propose. Perhaps the cyclic universe is not emotionally
satisfying, because it stands far from providing any kind of reassurance about the meaning of the
universe and our place in it. But it is potentially cognitively satisfying because it provides a
nonmysterious mechanism by which our universe could have come to be. If I someday write a second
edition of this book, I hope it will have a chapter section called “Branes and the Meaning of Life.”
Steinhardt and Turok reject the popular anthropic principle, according to which the complexity of
the universe is connected with our ability to exist in it as observers, as if the universe were somehow
fine-tuned to produce humans. They grant that the physical laws and conditions that govern the
universe must be compatible with the fact that life exists, but this fact tells us nothing about the origins
of those laws and conditions. Some physicists suggest that our planet lies in an unusual universe out
of a multiverse of possibilities, finely tuned as a prerequisite for life to evolve. In contrast, the cyclic
model sees our universe as arising from physical mechanisms, not abstract ideas such as the
multiverse and fine tuning to support life.