Let us journey into the heart of a black hole. We slip beyond its horizon and tumble down this crack in the universe. As we plunge, we see geometry fold. Time and space pull and stretch. And finally, at the black hole’s core, space and time dissolve, and a white hole is born.
One of the most remarkable aspects of Einstein’s relativity is that your time is not my time. The flow of time is relative. It can change. In particular it depends how fast observers (i.e., us) move in relation to each other or how close we are to massive bodies (like a black hole). So, to an outside observer, someone falling towards a black hole seems to have their clocks slow down until they stop entirely at the event horizon’s edge. How this works? How the flow of time is both personal and relative?
If we approach the horizon and go beyond it, our watches do not slow and nothing strange happens to the space around us, just as nothing peculiar happens to a ship when it crosses the line of the horizon and disappears from our view.
White Holes
by Carlo Rovelli
Let us journey, with beloved physicist Carlo Rovelli, into the heart of a black hole. We slip beyond its horizon and tumble down this crack in the universe. As we plunge, we see geometry fold. Time and space pull and stretch. And finally, at the black hole’s core, space and time dissolve, and a white hole is born.
Rovelli has dedicated his career to uniting the time-warping ideas of general relativity and the perplexing uncertainties of quantum mechanics. In White Holes, he reveals the mind of a scientist at work. He traces the ongoing adventure of his own cutting-edge research, investigating whether all black holes could eventually turn into white holes, equally compact objects in which the arrow of time is reversed.
Rovelli writes just as compellingly about the work of a scientist as he does the marvels of the universe. He shares the fear, uncertainty, and frequent disappointment of exploring hypotheses and unknown worlds, and the delight of chasing new ideas to unexpected conclusions. Guiding us beyond the horizon, he invites us to experience the fever and the disquiet of science—and the strange and startling life of a white hole.
In ‘White Holes,’ Carlo Rovelli takes readers beyond the black hole horizon
by Adam Frank
https://www.npr.org/2023/10/31/1209487538/book-review-carlo-rovelli-white-holes
Horizons are weird. They delimit what we can see in the distance, but they are also always personal: Walk 10 miles to the west and your horizon line moves 10 miles to the west with you.
Remarkably, this local, personal character of horizons also extends to black holes, the most enigmatic objects in the cosmos. Going beyond that horizon towards a new understanding of space, time and black holes is the principal goal of physicist Carlo Rovelli’s wonderful new book White Holes.
“What happens at the center of a Black Hole?” is one of those questions I get whenever I tell someone I’m an astrophysicist — and it’s the question that propels this book. Rovelli is unique among modern scientists who write for popular audiences in his ability to capture the purest essence of his science with both precision and lyricism. White Holes, like Rovelli’s other works, is remarkably short — less than 200 pages. But the clarity of his explanations is unparalleled. As a scientist who is also a popularizer, I often find myself marveling at the acuity of his passages. More than just an ability to explain cutting edge ideas in physics, Rovelli’s erudition and sensitivity lets him make contact with the broadest human yearnings for making sense of the world. This capacity is put to good use in White Holes, where the descent into a black hole is often narrated via quotes from Dante who made his own journey “down there in the blind world below.”
The science question at the heart of Rovelli’s new book comes from his own research into the intersection of Einstein’s General Theory of Relativity and Quantum Mechanics. The former identifies gravity with the shape of space and time. The latter determines the behavior of the nanoworld — i.e., atoms and their constituents. Black holes are a crossing point for these two great theories because they’re places where gravity is so strong that space and time become distorted on quantum scales.
Black holes form when so much matter accumulates in one location that no force can stop its contraction via gravity. Imagine a star that has used up its nuclear fuel and no longer produces energy to support itself against its own weight (the own “shining” thing is a just a consequence of this battle). As the fuel runs out, gravity squeezes the star down to ever smaller sizes. At some point the dead star is so small and dense that light emitted from its surface cannot escape gravity’s pull. In the language of Einstein, the curvature of surrounding space-time is too extreme for light to escape. That’s when a horizon forms around the black hole. This “event horizon” marks the point of no return. Observers outside the horizon can never get any information about what’s inside the horizon (that’s why it’s called a horizon).
Black holes are real. They have been observed in a number of ways including direct images using the entire Earth as a telescope. But even though physicists have seen black holes and developed many remarkable and sophisticated ideas about them, the eventual fate of matter falling into one remains a stubborn scientific mystery.
That’s where Rovelli and White Holes comes in. His answer to the question “What happens?” is that black holes eventually become white holes where everything that fell into event horizon emerges again. To demonstrate how this is possible, Rovelli takes the reader on a fascinating exploration of what a horizon means for time. One of the most remarkable aspects of Einstein’s relativity is that your time is not my time. The flow of time is relative. It can change. In particular it depends how fast observers (i.e., us) move in relation to each other or how close we are to massive bodies (like a black hole). So, to an outside observer, someone falling towards a black hole seems to have their clocks slow down until they stop entirely at the event horizon’s edge. Understanding how this works, how the flow of time is both personal and relative, represents some of Rovelli’s best work in the book. As he writes “… if we approach the [event] horizon and go beyond it, our watches do not slow and nothing strange happens to the space around us, just as nothing peculiar happens to a ship when it crosses the line of the horizon and disappears from our view.” From these observations Rovelli then builds a path for us towards a new theory of black holes and their fate.
I won’t spoil the ending by telling you what Rovelli says happens when black holes turn into white holes. I will, however, tell you that taking the journey with Rovelli is more than worth the price of the book. Dante gave us his tour of the underworld. We could not do better than having Rovelli as a guide into the dark world of black holes.
White Holes — Carlo Rovelli takes us on a flight into space and time
Physics meets philosophy — and Dante — in possibly the most charming book by a mainstream scientist this year
by Clive Cookson
https://www.ft.com/content/a7f6453b-243e-4138-b31f-c8ec81fc8836
Over the past few years, black holes have taken a compelling hold on scientific and popular discourse about cosmology and the nature of the universe. For many people these bizarre objects, which pack matter into a small space so densely that absolutely nothing can escape their gravitational pull, are the most fascinating objects in space.
Although some physicists started to predict their existence a century ago, as a consequence of Einstein’s theory of relativity, it took many decades of astronomical observations to move beyond the mathematics and produce compelling evidence that the universe really contains huge numbers of black holes. Even 20 years ago, many scientists questioned their reality. Today almost everyone is convinced not only that they exist, but that they play an essential role in the formation of stars and galaxies — indeed in the overall distribution of matter through space.
Now scientific speculation is building around objects that are the hypothetical inverse of black holes: white holes, which matter cannot enter but will eventually leave. Speculator-in-chief is Carlo Rovelli, the Italian theoretical physicist who is also a maestro of imaginative science writing.
Rovelli’s White Holes explores the subject in his characteristic style combining poetry, fantasy, philosophy and hard physics — which has placed him at the forefront of an innovative new wave of authors communicating science to general readers. We are guided by Dante’s Divine Comedy as well as by relativity and quantum mechanics. This slim volume must be the most unusual book published this year by a mainstream scientist.
“The hypothesis that black holes can transform into white . . . seems quite beautiful to me. I do not know if it is correct,” he writes disarmingly. “No one has seen a white hole. Yet.”
Before delving into white holes, Rovelli explores black ones, which were imaged for the first time in 2019. They form when the material that makes up massive stars or the centre of a galaxy falls in on itself until gravity overrides the other fundamental forces that keep the components of matter apart. After that, not even light can escape.
Rovelli borrows Dantean language to describe the geometry of space inside a black hole, “down there in the blind world below”. More precisely, Einstein’s equations imply that a black hole is not a ball or sphere but a funnel that grows ever longer and narrower with time. At the bottom is a so-called singularity, “the last depth and the darkest lair. And the farthest from Heaven which encircles all,” as Dante describes the deepest circle of Hell.
Then comes Rovelli’s speculative leap beyond Einstein. He invokes the counterintuitive weirdness of quantum physics to suggest that when matter is squeezed beyond the permissible limit of compression, there is a rebound. Black becomes white, a bit like Dante seeing Beatrice and suddenly being flooded with sunlight, and “we fly to the other side of space and time.”
A white hole is a black hole with time reversed, we learn. Nothing can escape a black hole until it suddenly turns white in a quantum fluctuation. After that, nothing can enter — and for a hypothetical observer inside the hole, time runs backward.
How long white holes are likely to last before they expel their contents in a burst of matter and energy remains unknown. Nor is it clear whether this material would reappear in our universe or another one. It is possible, Rovelli writes, that the Big Bang that launched the universe was an analogous cosmic rebound (“Big Bounce”) from a previous universe.
Billions of white holes may be floating around outer space, according to Rovelli. Like black holes, their existence would significantly affect the structure and future development of the universe. Their combined mass might even be sufficient to make a significant contribution to the mysterious and still unobserved “dark matter” that is known from its gravitational effects to pervade the cosmos.
White Holes will not please everyone, as Rovelli himself concedes. He removes as much physics jargon as possible, on the grounds that non-scientists would find such details burdensome, while experts “want a novel perspective” without technical language. This annoys “the intermediate type of reader” such as physics students, “because it grates to see details skipped that you have painstakingly studied and find things presented in a way that is different from the sacred (text) books.”
For me — someone whose knowledge of physics Rovelli would probably regard as intermediate — the book was sometimes hard to follow. And occasionally I was annoyed by his failure to address obvious questions, such as what it would take for astronomers actually to observe and then confirm the existence of a white hole.
But the overall argument of White Holes is clear. Like Rovelli’s previous books, its structure and language —thanks partly to his longtime translator Simon Carnell — have a charm that I found irresistible. No one else matches the way Rovelli describes the creative and imaginative thinking behind theoretical physics.
Trous blancs
de Carlo Rovelli
traduit par Matteo Smerlak
(sk)
Rovelli に導かれ、ブラックホールの中心への旅に出る。地平線を超えて、宇宙の亀裂に転がり落ちる。急降下すると、ジオメトリーが折り畳まれるのがわかる。時間と空間が引っ張られ、伸びてゆく。ブラックホールの中心部に着くと、時空が完全に溶け、ホワイトホールが誕生する。
でも、私のまわりは何も変わらない。地平線に近づいたり、地平線を超えたりしても、時計の針は遅れることなく、（船が地平線を越えて私たちの視界から消えたときに何も特別なことは起こらないのと同じように）私の周囲の空間には何も奇妙なことは起こらない。
あなたの時間は私の時間ではない。時間の流れは相対的なもので、変わる可能性がある。それは、私たちが「お互いにどのくらい速く移動するか」「どのくらいブラックホールのような巨大な天体に近づくか」によって決まる。あなたには、ブラックホールに向かって落ちていく私は、事象の地平線の端で完全に停止するまで時計が遅くなっているように見える。
そもそも、ホワイトホールは、誕生などしてはいない。ブラックホールが白くなっただけ、時間が逆転しただけなのだ。ブラックホールが量子ゆらぎで突然白くなるまで、私はブラックホールから逃れることができない。白くなった後は何も入ることができなくなる。私には何も変わらなくても、あなたにはホワイトホールのなかの時間は逆行している。
あなたの時間と私の時間は違う？ それとも違うように見える？ 時間の流れは、どのように「個人的」で「相対的」なのか? そもそも、時間の流れは「絶対的」ではないのか？
これを書いていて、私は少しおかしくなっている。自分の知っている世界を離れ、知らない世界に入っていけば、自分の常識も、直感も、知識も、何の役にも立たなくなる。それはわかる。でも常識は最後までまとわりつき、直感は違うと言い続け、知識は最後まで捨てられず、新しいことの理解の邪魔をする。
私が Rovelli に近づくことは、永遠にない。