Black Holes and Radiometry

Following Grischuk and Sidorov [Phys. Rev. D 42 (1990) 3413] in putting the Bogolubov-Hawking coefficient of Schwarzschild black-holes in the squeezing perspective, we provide a short discussion of Schwarzschild black holes as radiometric standards. In this work I will give arguments in favour of taking Schwarzschild black holes (SBH) as blackbody simulators, most probably the best ones. Even before the discovery of their " horizon " radiation, [1], SBHs might have been considered in the special class of " material " bodies in the Universe to be selected as blackbody simulators. In classical physics/relativity the horizon surface of a SBH absorbs all the radiation falling on it. This is nothing else but the common definition of a blackbody (i.e., absorptivity α = 1). The radiometric considerations to follow stem from the connections between the theory of " particle creation " in external fields and the quantum-mechanical theory of squeezed states. In the seminal paper [2], Grishchuk and Sidorov hinted on the close relationships of the two research fields, and they suggested the observed large-scale structure of the Universe to be just a strongly squeezed state of the zero-point quantum fluctuations of a cosmological scalar field. In the case of a scalar quantised field in the SBH gravitational field, a two-mode squeeze operator comes into play in order to relate the in-and out-vacuum. This is so because Hawking radiation is a manifestation of the decomposition of the field over travelling waves in a region with rather complicated causal structure, involving conditions on base fields not only at spatial