White Holes: Inside the Horizon
by Carlo Rovelli (2023; Allen Lane / Penguin; 147 pages)
Black and White Thinking
We are “familiar” with black holes, but this book is about what Carlo Rovelli and collaborators call white holes. In summary, a black hole is seen from the outside, where near a massive compact object (e.g. a collapsed star) the gravity becomes so strong that the distortion of space-time means that even light cannot escape. That is why it appears black. A white hole is the same thing, but seen from the inside.
Of course no one has ever seen inside a black hole, nor do I imagine anyone ever will. But the same mathematics that predicted the existence of black holes long before one was (indirectly) detected, can also be extrapolated inside that black horizon, to explore (or at least speculate) what likes within. Or should that read “what lies beyond”?
Bouncing Star
Following the maths, he traces the path of the collapsing star towards what some dub a “singularity”, but which scientists cannot accept. Rovelli and collaborators have not shied away from the hard sums that appear to show the star “bouncing” back into a mini-universe in which time has apparently reversed?!
What do we make of this Alice Through the Looking Glass physics? I struggle with some strands of speculative science, pushing mathematical concepts beyond the realm they were conceived for, and which leaves me unsure of the foundations of his theories. He is one of the authors of the theory of quantum loop gravity, which seeks to reconcile the otherwise unhappy couple of Quantum Mechanics and Einstein’s General Theory of Relativity. There are probably only a handful of theoretical physicists in the world who could genuinely follow and critique Rovelli’s workings, so we have to take much of it on trust.
Who is this for?
Rovelli is a best-selling author and fascinating character, and not afraid of criticism or controversy. His scientific speculations are sometimes on the fringe of “respectable” mainstream physics, but rather like Roger Penrose, he is no doubt a brilliant mathematician, physicist and writer. He is also a fearless advocate for peace, unafraid to confront politicians, for which I think he is admirable.
He is also a cultured man and is proud of his Italian heritage. Yet I had not expected quite so many quotations in a science book from Dante Alighiere’s astonishing 14th century poem The Divine Comedy, with its unforgettable journeys through hell, purgatory and paradise. And at the same time Rovelli’s book has not a single equation! This is a short book – you can read it in an afternoon, even if it takes a lot longer to take in the ideas. Yet who is it for? It is popular science, and demands some familiarity with concepts of astrophysics; but how many readers of popular science books have read and appreciated Dante’s poetry? I was baffled, in more ways than one.
Elsewhere
- For an experience of 14th century cosmology, I recommend the Penguin edition of The Divine Comedy; brilliantly translated by Dorothy L Sayers. This was published in the early 1960s and in my opinion brilliantly preserves the rhyme and metre of Dante’s original verse.
- For another short book by Carlo Rovelli, try Anaximander and the Nature of Science (Penguin, 2009/2023; 209 pages). The Greek philosopher of the 6th century BCE is an inspiration to Rovelli, who aspires to the ancient’s leaps of imagination.
- Ian Stewart, Calculating the Cosmos: How Mathematics Unveils the Universe (Profile Books 2016/17; 346 pages). Stewart discusses white holes as conceived by British mathematician Roger Penrose. This is a brilliant book which traces how often mathematics has led the way towards discovery of new real objects in the Universe.
- Max Tegmark, Our Mathematical Universe: My Quest for the Ultimate Nature of Reality (Penguin, 2015; 432 pages). Tegmark goes one step further than Stewart, in that his thesis is that the Universe IS a mathematical object. I’m glad I read it. I don’t want to read it again. Instead of providing a description to help us understand reality, I think Tegmark’s book loses touch with reality.