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Energy, entropy, and spacetime : lessons from semiclassical black holes Costa, Bruno Arderucio


This doctoral thesis explores semiclassical effects on black hole physics. Semiclassical theory refers to the application of quantum field theory in curved, classical background geometries, which respond to the expectation value of the regularised stress-energy tensor of the quantum matter. Among the original findings, I develop a few useful techniques to help regularise the stress-energy tensor in two dimensions. I apply them to a model of stellar collapse to analyse the importance of quantum mechanical effects in the collapse itself. I find an explicit example showing that the behaviour of the late-time Hawking radiation does not depend on the details of the collapse and argue that any quantum mechanical effect is negligible for the collapse of an astrophysical object (whose mass is comparable to the solar mass). In the realm of black hole thermodynamics, I prove the first law for stationary black holes and propose a definition for the entropy in piecewise stationary black holes which I show to obey the generalised second law of thermodynamics. After also discussing the zeroth law, it becomes clear that this set of laws is rooted in semiclassical physics and give the hypotheses which are necessary for it to hold. My derivation of the laws of black hole thermodynamics also contributes towards the answer to the long-standing question of interpreting the Bekenstein-Hawking entropy. My work suggests that it is understood from the information perspective as accounting for the information hidden behind the horizon.

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