In 1900 the world-renowned mathematician David Hilbert presented twenty-three problems at the International Congress of Mathematicians in Paris. These problems have inspired mathematicians throughout the last century. Indeed, Hilbert’s address has had a profound impact on the direction of mathematics, reaching far beyond the original twenty-three problems themselves. As a piece of millennial madness, all participants of the Strings 2000 Conference were invited to help formulate the ten most important unsolved problems in fundamental physics. Each participant was allowed to submit one candidate problem for consideration. To qualify, the problem must not only have been important but also well-defined and stated in a clear way.

The best 10 problems were selected at the end of the conference by a selection panel consisting of:

* Michael Duff (University of Michigan)

* David Gross (Institute for Theoretical Physics, Santa Barbara)

* Edward Witten (Caltech & Institute for Advanced Studies)

Here are the problems:

1. Are all the (measurable) dimensionless parameters that characterize the physical universe calculable in principle or are some merely determined by historical or quantum mechanical accident and uncalculable? David Gross, Institute for Theoretical Physics, University of California, Santa Barbara

2. How can quantum gravity help explain the origin of the universe? Edward Witten, California Institute of Technology and Institute for Advanced Study, Princeton

3. What is the lifetime of the proton and how do we understand it? Steve Gubser, Princeton University and California Institute of Technology

4. Is Nature supersymmetric, and if so, how is supersymmetry broken? Sergio Ferrara, CERN (European Laboratory of Particle Physics) Gordon Kane, University of Michigan

5. Why does the universe appear to have one time and three space dimensions? Shamit Kachru, University of California, Berkeley Sunil Mukhi, Tata Institute of Fundamental Research Hiroshi Ooguri, California Institute of Technology

6. Why does the cosmological constant have the value that it has, is it zero and is it really constant? Andrew Chamblin, Massachusetts Institute of Technology Renata Kallosh, Stanford University

7. What are the fundamental degrees of freedom of M-theory (the theory whose low-energy limit is eleven-dimensional supergravity and which subsumes the five consistent superstring theories) and does the theory describe Nature? Louise Dolan, University of North Carolina, Chapel Hill Annamaria Sinkovics, Spinoza Institute Billy & Linda Rose, San Antonio College

8. What is the resolution of the black hole information paradox? Tibra Ali, Department of Applied Mathematics and Theoretical Physics, Cambridge Samir Mathur, Ohio State University

9. What physics explains the enormous disparity between the gravitational scale and the typical mass scale of the elementary particles? Matt Strassler, Institute for Advanced Study, Princeton

10. Can we quantitatively understand quark and gluon confinement in Quantum Chromodynamics and the existence of a mass gap?