As we well know, a black hole is the point at which gravity wins over everything: nothing, not even light, should be able to escape it. For decades that was the conclusion of general relativity. Then Stephen Hawking arrived, and that certainty — solid as it was — was no longer enough. In its place he proposed an idea with truly unique features: black holes are not entirely black. They radiate. They evaporate. They have a temperature. The insight dates from 1974. Hawking joined Einstein’s relativity to quantum mechanics and discovered that, at the edge of a black hole — the event horizon — space is not empty. Pairs of particles are born and then split apart: one falls in, the other escapes. Seen from outside, that escape is heat. It is called Hawking radiation. The smaller the black hole, the hotter it is; the more it radiates, the more mass it loses, until it may even disappear. The theory accounts for phenomena that Einstein’s geometry alone left unresolved. A black hole has an entropy linked to the area of its horizon, not to its volume: it is one of the most beautiful results of twentieth-century physics. It has a temperature. And it poses a problem that is still open, the information paradox: if the hole evaporates, what becomes of what fell inside? Hawking himself changed his mind more than once. The question is still alive.
It is not a laboratory accessory, and you cannot wear it. It is a map of the extreme: it serves those who study the universe, those who seek to unite gravity and the quantum, and anyone who wants to know whether even “nothing” can burn. It is fifty years old and it continues to spark debate. Few human “inventions” can say the same. If you are interested in publishing one of your own (and wish to protect it properly first), contact us at the telephone numbers given at the bottom of the page, or write to us using the ELECTRONIC FORM. Visitors are reminded that the texts in this section are protected by copyright, which forbids their total or partial reproduction. The scientific theories presented here belong to the heritage of knowledge; their presentation on these pages is protected as an original work.