If you think black holes are strange, white holes will blow your mind
ESA/V. Beckmann (NASA-GSFC By Carlo Rovelli NEVER trust the textbooks, even the ones written by great scientists. In his celebrated 1972 tome Gravitation and Cosmology, Nobel prizewinning physicist Steven Weinberg called the existence of black holes “very hypothetical”, writing that “there is no [black hole] in the gravitational field of any known object of the universe”. He was dead wrong. Radio astronomers had already been detecting signals from matter falling into black holes for decades without realising. Today we have lots of evidence that the sky is teeming with them. The story may now be repeating itself with white holes, which are essentially black holes in reverse. In another renowned textbook, the world-leading relativity theorist Bob Wald wrote that “there is no reason to believe that any region of the universe corresponds to” a white hole – and this is still the dominant opinion today. But several research groups around the world, including my group in Marseille, have recently begun to investigate the possibility that quantum mechanics could open a channel for these white holes to form. The sky might be teeming with white holes, too. The reason to suspect white holes exist is that they could solve an open mystery: what goes on at the centre of a black hole. We see great amounts of matter spiralling around black holes and then falling in. All this falling matter crosses the surface of the hole, the “horizon” or point of no return, plummets towards the centre, and then?