Abstract
String theory is a promising attempt to unify the two cornerstones of Physics: the Standard Model of particle physics and Einstein’s theory of General Relativity. In addition to strings we now know that string theory contains other extended objects of various dimensions called “branes”. The properties of these branes have lead to important insights into the non-perturbative structure of the theory. In particular, the five perturbative string theories in ten spacetime dimensions and a new theory in eleven dimensions that doesn’t contain strings are now understood to be different limits of a more fundamental theory christened M-theory. We discuss these developments as well as two applications: one to black hole physics and the other to quantum field theory.
Black holes are key laboratories for exploring aspects of quantum gravity. The foundational work of Stephen Hawking and others revealed that black holes are thermal objects with a characteristic temperature and an entropy given, in Planck units, by exactly one quarter of the area of the event horizon of the black hole. An important challenge is to provide a precise microscopic, statistical mechanical, interpretation of black entropy. Using branes this has been achieved for certain black holes in string theory.
Another key discovery in string theory, again using branes, is the realisation that certain quantum field theories in four (say) spacetime dimensions are actually equivalent to string theory in certain ten-dimensional spacetimes. This provides a dramatic new picture of quantum field theory and reveals string theory to be a powerful tool for analysing quatum field theory independent of its status as a theory unifying all of Physics. Conversely, the equivalence is remarkable in that it shows that non-perturbative string theory, in certain backgrounds, is actually quantum field theory.
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Professor Jerome Gauntlett
All photos taken by Meilin Sancho