Three Roads To Quantum Gravity

POSTSCRIPT 223
Chopin Soo and Martin Bojowald, has led to a greatly improved
understanding of how classical cosmology emerges
from loop quantum gravity. New calculational methods for
spin foams have given us very satisfactory results. Large
classes of calculations, for example, turn out to give finite,
well-defined answers, where conventional quantum theories
gave infinities. These results present more evidence that
loop quantum gravity provides a consistent framework for a
quantum theory of gravity.
Before closing I want to emphasize again that this book describes
science in the making. There are some people who
think that popular science should be restricted to reporting
discoveries that have been completely confirmed experimentally,
leaving no room for controversy among experts.
But restricting popular science in this way blurs the line
between science and dogma, and dictates how we believe
the public should think. To communicate how science really
works, we must open the door and let the public
watch as we go about searching for the truth. Our task is to
present all the evidence and invite the readers to think for
themselves.
But this is the paradox of science: It is an organized, even
ritualized, community designed to support the process of a
large number of people thinking for themselves and discussing
and arguing the conclusions they come to.
Exposing the debates in a field like quantum gravity to the
public is also bound to raise controversy among experts. In
this book, I tried to treat the different approaches to quantum
gravity as evenhandedly as possible. Still, some experts have
told me I do not praise string theory enough, whereas others
have told me I did not emphasize its shortcomings nearly
enough. Some colleagues complained that I did not champion
my own field of loop quantum gravity strongly enough,
given that string theorists generally fail to even mention loop
quantum gravity—or anything other than string theory—in
their own books and public talks. Indeed, one string theorist
who reviewed the book called me a “maverick” for even