Carlo Rovelli (Allen Lane)
WHAT happens if you fall into a black hole?
It is one of the most intriguing and complex questions ever conceived. Black holes are places where, at their heart, general relativity breaks down. They are objects that even Albert Einstein thought wouldn’t exist in the universe. Yet we know that they do: in the past few years, we have even captured images of them.
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I imagine that, like many of us, theoretical physicist Carlo Rovelli was amazed when the first picture of a black hole was released in 2019. But for him, the image was perhaps more meaningful. “I’d studied black holes all my life, without knowing if they truly existed or not,” he writes in his latest book. “Here is the visual evidence, something I could never have imagined when I was a university student and was first charmed by these strange phenomena.”
Now, imagine black holes going backwards in time. Instead of matter falling into them, everything inside them must leave. These are white holes – the subject, and title, of Rovelli’s new book.
Over the past few years (including in previous 91av book reviews), Rovelli has been called “the poet of physics”. This is a title he very much lives up to in White Holes: Inside the horizon, which feels more like an ode to the biggest questions in physics – concerning stars, black holes and the nature of time – than any kind of conventional popular physics book.
Perhaps it is the book’s length: at a refreshing 150 pages, it can be consumed in a single sitting. Or maybe it is the references to The Divine Comedy by Dante peppered throughout the book. Either way, the poetic nature of White Holes makes for an enjoyable and enlightening read: great for anyone who likes to indulge in musings about extreme physics that border on the existential.
Much like The Divine Comedy, White Holes is a journey that takes place in three parts. But instead of the depths of hell, Rovelli plunges us into a black hole. We venture to a place where gravity is so extreme that nothing, not even light, can escape, “where time appears to slow until it stops, and space seems to end”, he writes.
Down we go, through the event horizon, dispelling some common misconceptions about the meaning of words like singularity along the way. What results is one of the clearest pictures I have encountered about the physics inside these extreme objects – and I have read a lot of descriptions of black holes.
There are some detours en route, although Rovelli is gracious to any readers who want to stick closely to the parts about black and white holes: “you can always skip ahead if you are a hasty reader”, he writes. We learn about the conceptual leaps taken by some of history’s most celebrated scientists, hear Rovelli’s own experience of developing the idea of white holes with his colleague, Hal Haggard, and consider free will and the flow of time.
Ultimately, though, the idea at the heart of the book is simple: white holes could exist in the universe.
This concept will be so alien to most people that Rovelli’s book could easily have become very unsettling. But by introducing the concept of black holes as something many physicists doubted the existence of, even a mere 20 years ago, Rovelli opens readers’ minds to the possibility, and the hope, that their counterparts exist.
You probably won’t ever fall into a black hole (or exit a white hole), but reading this might be the next best thing.
