I have the following article for explanation of Hawking - Unruh radiation: http://arxiv.org/PS_cache/quant-ph/pdf/0401/0401170.pdf. It is the most simple explanation of Hawking radiation until now. Peoples try to find microscopic explanation of this, but, thermal properties of matter are not dependend of matter's precise micro-properties. And the model above gives macroscopically right properties. So can anyone give explanation why formule above gives precisely thermal spectrum of radiation. Why at constant acceleration and not at some different example. Thermal spectrum is very primary thing, so derivation above is still to long. It is not question for me, which quantum gravity theory is OK, but why the semi-classical theory above gives precisely thermical spectrum.