Heidelberg 2022 – wissenschaftliches Programm
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AGPhil: Arbeitsgruppe Philosophie der Physik
AGPhil 6: Foundations of Gravity
AGPhil 6.4: Vortrag
Mittwoch, 23. März 2022, 15:45–16:15, AGPhil-H14
On the relation between Unruh and Hawking radiation — Ignacio Araya1 and •Siddharth Muthukrishnan2 — 1ICEN, Universidad Arturo Prat, 1110939, Iquique, Chile — 2HPS, University of Pittsburgh, Pittsburgh, PA, USA 15260
It is often said that Hawking radiation just is a kind of Unruh radiation. In this work, we clarify the ways in which Hawking radiation can and cannot be seen as a kind of Unruh radiation. Hawking radiation is analogous to Unruh radiation in that the Schwarzschild metric near the horizon is isomorphic to the Rindler metric, which allows us to employ the derivation of Unruh radiation to obtain Hawking radiation. But the isomorphism is restricted to the near-horizon region. This observation leads to the way in which Hawking radiation is not a kind of Unruh radiation: the analogy between them is not due to the equivalence principle. One might think that because observers near -- but outside of -- the horizon of a black hole are equivalent, via the equivalence principle, to an accelerating observer in empty space, Hawking radiation observed by a hovering observer outside a black hole just is the kind of Unruh radiation that an accelerating observer in empty space would see. We argue that this is an incorrect way of thinking of Hawking radiation. Indeed, this would imply that hovering observers outside gravitating bodies that are not black holes -- such as stars and planets -- would also observe Unruh/Hawking radiation, and this is not the case. Throughout we emphasize the ways in which Hawking and Unruh radiation can be seen as varieties of geometric radiation, i.e., radiation generated by the structure of a metric containing horizons.