HOW YOUR GUITAR WORKS | Kirkus Reviews

The bestselling author and theoretical physicist looks at “the elusive younger siblings of black holes.”

Since white holes may be an inevitable consequence of black holes, Rovelli, the author of Seven Brief Lessons in Physics and Reality Is Not What It Seems, begins with an explanation, noting that white holes are essentially the reverse of a black hole. Since the 18th century, scientists knew that, as a universal force, gravity from an extremely massive star should slow its light’s speed to zero. That concept made little sense until Einstein showed that light never slows but that gravity distorts space, so light near a massive body appears to curve. The more massive the body, the greater the curve until the light doubles back. Einstein insisted that no such body existed, but his equations permit it, and they eventually turned up. All stars eventually run out of fuel and collapse. Average stars like our sun end up as tiny, immensely dense dwarfs. The largest stars, however, continue to collapse, ultimately to an infinitely tiny, infinitely dense point. Their light doubles back, resulting in a black hole, from which nothing that enters can leave. Even time stops dead at its edge, or “event horizon.” Mathematics, Einstein’s included, doesn’t work when dimensions are infinitely small or large, so physicists don’t know what happens when a black hole forms. That hasn’t stopped them from speculating, and Rovelli leads one school favoring the production of white holes, a bizarre concept that is still purely theoretical. Calling on quantum mechanics, which deals with minuscule phenomena, he explains that the collapsing star never becomes infinitely small but “bounces,” leading to a white hole. There, matter can leave but never enter; “a white hole is a black hole with time reversed.” Rovelli works hard, sometimes successfully, to explain matters, but he is dealing with phenomena so complex that he often gives readers permission to skip ahead.

Heavy-duty popular science not for the faint of heart.