E. Witten, "On the structure of the topological phase of two-dimensional gravity," Nuclear Physics B, 340:281-332, 1990.
Edward Witten (School of Natural Sciences, Institute for Advanced Study, Princeton, N.J.):
"There was a long-standing mathematical problem of calculating intersection numbers of certain submanifolds of the moduli space of Riemann surfaces. As a result of my earlier work on Donaldson theory, I knew that such problems can be formulated in the language of quantum field theory. I wondered if this would give some insight and puttered around with it for a while without getting anywhere.
"Then, another problem arose of whether two-dimensional random surfaces had a geometrical interpretation of a more classical kind. Again, I puttered around with this without much insight.
"Then in widely cited papers, D.J. Gross and A.A. Migdal (Physical Review Letters, 64:127-30, 1990 [Hot Papers, The Scientist, March 2, 1992, page 15]), M.R. Douglas and S.H. Shenker (Nuclear...