Ultraplanckian scattering, black holes, and the problems of quantum gravity

Speaker: 
Steve Giddings (UC Santa Barbara)
Event Date and Time: 
Thu, 2012-01-12 16:00 - 17:00
Location: 
Hennings 201
Local Contact: 
Gordon Semenoff
Intended Audience: 
Undergraduate
Reconciling quantum mechanics with gravity is perhaps the most conceptually profound unsolved problem from twentieth century physics. Gedanken experiments have a long tradition in unravelling difficult problems. One such experiment exposing a central issue in quantum gravity is that of scattering particles at energies above the Planck scale. Such collisions might even be realized at LHC, in certain theories of nature. In a classical description of this scattering, black holes form; Hawking showed quantum effects then cause their evaporation. But, attempts to give a complete quantum mechanical description of this process have lead to an apparent paradox, driving at the heart of the problem of quantum gravity, and which seems conceptually much deeper than the 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.
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