- Broida 1640
Steve Giddings - UCSB
Reconciling quantum mechanics with gravity is perhaps the most conceptually profound unsolved problem from twentieth century physics. A gedanken experiment exposing a possibly central issue is that of scattering particles at energies above the Planck scale. Such collisions might even be realized at the LHC, in certain theories of nature. Classically, these can produce black holes, which Hawking showed evaporate through quantum effects. But attempts to give a complete quantum mechanical description of this process lead to an apparent paradox, driving at the heart of the problem of quantum gravity, and which seems much deeper than commonly-discussed issues of nonrenormalizability or singularities. This has motivated new ideas in string theory, but the ultimate resolution may be beyond, and require new physical principles. Hints come from inflationary cosmology, quantum information theory, and study of the S-matrix . This problem particularly raises questions about the role of macroscopic spacetime locality in physics, and the possibility that such locality only emerges as an approximate concept.