Black Holes: The End of the Universe? by John Taylor was the first book I bought with my own hard-earned cash from a poorly paid paper round. It was 1974, I was 11. It was the subtitle that grabbed my attention, since I’d never heard of black holes. At the time these mysterious cosmic objects were merely a theoretical possibility, but a half-century later we have ample evidence that they really do exist. After writing bestsellers about quantum mechanics, time, and the nature of reality, Italian physicist Carlo Rovelli weaves all three together in his latest book, taking us on a journey deep inside a black hole. An accomplished storyteller, Rovelli begins this mind-boggling ride by explaining how they form.
Sooner or later, stars run out of fuel and stop shining. At that point, their own gravity causes them to become compressed. Our sun will end up as a so-called white dwarf, its mass squeezed until it’s the size of the Earth. However, some stars are so massive, with such strong gravity, that the collapse continues until they’re squeezed to a point known as a singularity. That’s where the known laws of physics break down. A black hole is a singularity surrounded by its event horizon, a one-way boundary shielding it from the rest of the universe. Anything that gets too close will be unable to escape, dragged into the hole and crushed out of existence. This is the conventional view, one that Rovelli challenges in his short, utterly engaging and densely packed narrative that you may have to read more than once.
According to Einstein’s theory of general relativity, the interior of a black hole is shaped like a funnel that becomes longer and narrower with time. At the bottom sits the remnant of the star that gave rise to the black hole. Rovelli argues the collapsing star hasn’t reached the bottom but is still falling because of the effect gravity has on time. And as space and time dissolve in a cloud of quantum probabilities, a black hole becomes a white hole, with time reversed. White holes, Rovelli explains, are how a black hole would appear if we could film it and run the video backwards.
Confused? Well, it’s hard enough to explain in a book, let alone a review. Even some professionals struggle to fully grasp these mind-bendingly counterintuitive concepts. And while Rovelli avoids the technical jargon of the physicist’s trade he does give the reader licence to skip the odd paragraph or page here and there. Thankfully, Einstein himself lets us off the hook, at least a bit: “imagination is more important than knowledge”, he once wrote. None of which is to say that you finish White Holes less well informed than you began it – and Rovelli certainly does an excellent job of conveying the wonder and strangeness of the universe. At the end, however, you may feel entitled to pour yourself a drink and savour the feeling of your mind stretching back into shape.