White Holes

This mind-bending outing by physicist Rovelli (Anaximander) explores the possibility of the existence of white holes, the hypothesized inverse of black holes. He explains that black holes were first proposed as a consequence of Einstein’s equations on general relativity, but because the equations “do not specify a direction for time,” it’s possible to run them with “the sign of the time variable flipped,” meaning that there may a point at which a black hole “rebounds and retraces its previous route in time, like a basketball bouncing.” After a black hole passes such a point, it becomes a white hole. If humans were able to survive inside a black hole, Rovelli suggests, they could reach the bottom and then “cross through and emerge into a white hole where time is reversed,” spending no more than a few seconds inside but emerging billions of years later due to the dilation of time. Rovelli does a solid job of making the underlying science accessible, even if some of the finer points may go over general readers’ heads, such as his explanation of why “you can only enter a black hole, and you can only exit a white hole.” Still, those with a background in physics will be sucked in. Photos. (Oct.)