Three Roads To Quantum Gravity

118 THREE ROADS TO QUANTUM GRAVITY
speci®c simplifying assumptions. Either the dimensionality
of space is reduced from three to one, or a great deal of
additional symmetry is added, which leads to a theory that
can be understood much more easily. But even if it has not yet
solved the problem that inspired its invention, duality has
turned out to be a central concept in quantum gravity. How
this happened is a very typical tale of how good scienti®c
ideas can spread far from their point of origin, for I rather
doubt that either Wilson or Polyakov originally considered
how their idea might be applied to a quantum theory of
gravity.
Like many good ideas, this one needed several goes to get it
right. Inspired by what I had heard from Wilson and
Polyakov, and further lessons on lattice theories I got from
Gerard 't Hooft, Michael Peskin and Stephen Shenker during
my ®rst year of graduate school, I set out to formulate
quantum gravity in terms of Wilson's lattice theory. Using
some ideas borrowed from several people, I was able to
concoct such a theory, which enabled me to spend a year or
so learning the various techniques developed by Polyakov,
Wilson and others by applying them to my version of
quantum gravity. I wrote up and sent out a long paper about
it and waited for a reaction. As was common in those days,
the only response was a stack of postcards from far-away
places requesting copies of the paper. There was of course the
inevitable request from the U.S. Army research lab, which
reminded us that someone somewhere was being paid to
think about the possible military applications of whatever
young graduate students were up to. It is strange to recall
those days, not so long ago, when we typed our papers on
IBM Selectric typewriters, got a professional in the basement
to draw the illustrations, and then stuffed the copies
individually into envelopes and mailed them out. These
days we write our papers on laptops and upload them to
electronic archives from where they are immediately available
on the Internet. I doubt many of our current students
have seen either an IBM Selectric typewriter or a postcard
requesting a preprint. Many have never even gone to the
library to read a paper printed in a journal.