The Gravity of Knowledge
---- Acknowledgements -----
An earlier version of this paper circulated under the title "Gravity in the Weightless Economy". We thank four referees, Robert Mo¢ tt and Dirk Krueger as editors, and Nick Bloom, Gene Grossman, Stefania Garetto, Gordon Hanson, Ann Harrison, Pete Klenow, Rod Ludema, Jim Markusen, Marc Melitz, Ulrich Muller, Jim Rauch, Carol Shiue, Eric Verhoogen, Jonathan Vogel, Bill Zeile, as well as seminar participants at the 2008 Philadelphia Fed Trade Conference, the 2009 NBER ITO conference, the 2010 NBER ITI Summer Institute, Colorado, Columbia, Georgetown, George Washington, Hong Kong, Hong Kong Science and Technology, LSE, Paris School of Economics, Stanford, UBC, and Utrecht for useful comments. We also thank Gordon Hanson for providing us with data. The statistical analysis of rm-level data on U.S. multinational corporations reported in this study was conducted at U.S. Bureau of Economic Analysis under arrangements that maintained legal confidentiality requirements. Views expressed are those of the authors and do not necessarily reflect those of the Bureau of Economic Analysis, nor of the National Bureau of Economic Research.