Dear Rovelli, you don’t need oriental mysticism to study black holes

Umberto Minopoli, a dear friend of Il Foglio, passed away last Saturday at the age of 69. This is an article he had written a few days before being hospitalized. Today in Rome, at 2.30 pm, in the Chamber of Commerce of Rome, via de’ Burrò 147, some friends of Umberto will remember him for a last farewell.

What is hidden inside a black hole? Where does that precipice of spacetime lead? Can you understand what you have never seen? Carlo Rovelli asks himself this in his latest work, “White Holes: Inside the Horizon” (Milan 2023). Two photos captured by the Event Horizon Telescope – the one (2021) of the black hole at the center of the M87 galaxy, 55 million light years from the Sun and the one (2023) of Sagittarius A, at the center of the Milky Way, 26,000 light years from us – have closed a discussion that has enthralled three centuries of scientific debate: black holes really exist. They are no longer hypotheses on which physicists make bets (the famous one between Hawking and Kip Thorne, in 1974, with a Penthouse collection up for grabs). Black holes, therefore, can be seen. But what are they hiding inside? Where would it lead to cross the mysterious border, that disturbing and dark region at the center of a crown of incandescent material, in furious rotation, which physicists call the event horizon?

It is not an imaginary line – as we imagine our horizons – but the enigmatic locked door of a particular area of ​​space and time: a place where events, the way events and nature manifest themselves that we know, literally , stop at the sight of an observer. For over 50 years, the black hole has been speculation, imagination, literature, even accurate film fantasy: the last one is magnificent, that of “Interstellar”, the masterful film by Christopher Nolan with the advice of Kip Thorne, Physics Nobel and father of black holes. Now, we see these monsters of a shocking universe that is unfolding before our eyes in the photos and we perceive them in the signals of the large interferometers which finally capture gravitational waves. It is possible to try to advance scientific hypotheses, now that we see them exist, on what should happen inside black holes. The professor. Rovelli takes up the question that has fascinated theoretical physics since the early 1970s and answers it with the arguments he has developed over 50 years of reflection on the most enigmatic phenomenon in the universe. The black hole is the place of undisputed dominion of gravity, where it has won every rival and where therefore, as in Dante’s inferno, there is only one destiny: to fall. A black hole is a collapsed star, whose matter whirls down, curving space and time – predict Einstein’s field equations – without brakes, shrinking and concentrating, ending up in a point of infinite density, which Physics calls a singularity . The funnel, beyond the event horizon, is where space and time become distorted. And nothing works according to the logic of the “outside world”. Above all time is upset: it is not what we know, past and future are reversed. For example: the collapsed star that has perhaps become centuries old would appear to be falling again in a few seconds. As if his future was ahead of the star’s past. All so magical and fantastic, but all rigorously deduced from the equations of relativity, adapted to the shocking numbers of that infernal environment. Rovelli reconstructs, with a rich set of arguments from relativistic and quantum physics, how the experience of that funnel of the universe could manifest itself to an object that fell into it: what it would encounter in the precipice and where the fall could end. The singularity, with its roller coaster between past and future, is the second limit, after the event horizon, that would be encountered in the black hole. Einstein’s relativity goes silent in the unspeakable environment of the singularity: he literally cannot tell us anything about the outcome of the fall. The material reality in that place doesn’t work with the laws of physics that we know. It has become quantum: it works with the strange, counterintuitive, ineffable behaviors of quantum physics. And it is logical that it is so. Behind the event horizon there is no longer a macroscopic world, made up of solid objects, of clotted matter: gravity, which crushes furiously, reduces everything to the microscopic matter of dimensionless particles. What would an outside observer looking at the exit of a black hole, the end of the funnel, see happening? Rovelli puts forward a hypothesis: the black hole could end up in a white hole. That is, in a region of spacetime, of the real universe, in which exactly the opposite properties of the entrance to the black hole, of the event horizon, hold. The end of the black hole could be the symmetrical stand-in of the original hole: things rise instead of falling; from the hole you go out but you don’t enter; it is white (shining with light and energy) rather than black (and trapping light); distorted time reverses (the future of what comes out is probably behind and not ahead. That’s quantum reality, guys. Fantasy?

White hole physics respects solid laws of nature: that of conservation of energy (otherwise denied by a black hole that swallowed matter without returning anything), that of symmetry. In a world of subatomic particles (the black hole is), every particle has its symmetrical counterpart. The white hole, therefore, is physically plausible. Rovelli, however, is our critical observation, he should leave it as it is: a seductive hypothesis, to be verified with the progress of physics. Instead, the militant Rovelli peeps out, that of the crisis in the West in the letter to the newspaper (Friday 28 March). The surrender of Physics, its aphasia on the inside of the black hole is emphasized by Professor Rovelli as an insurmountable limit of Western thought, almost a boundary of knowledge: there “we have reached”, writes Rovelli, “the edge of our knowledge”. To penetrate the precipice of the event horizon, we need a new thought, a new language of science, beyond the “logical and mathematical rigidity” and syllogisms of what, from Galileo to Einstein, is the language of Western thought. Here indeed, the thought of the physicist Rovelli becomes dizzying. We should resort, writes the professor, to oriental thought, curiously, exemplified in currents of Chinese mysticism (Moism and the thought of Zhuang-zi) of the third century BC It would teach to “argue by analogies”, drawing on art, using the creativity and freeing scientific thought from the logical and mathematical syllogisms of the Western tradition.

This reservation about Western physics and science is where the theoretical physicist gives way to the militant thinker. The truth is exactly the opposite of an alleged crisis or inadequacy of Western scientific thought to deal with the new frontiers of knowledge of the cosmos. Western Physics is the field of scientific knowledge where the progress of knowledge has made surprising advances in 30 years. Changing an age-old idea of ​​the universe, discovering an unexpected functioning and opening up science to new and unexpected questions. Eastern mysticism will be unable to tell us anything about the knowledge of black holes, together with dark matter and energy, the most compelling question in the physics of the universe. Instead, the research of contemporary Physics will be needed: studies on quantum gravity (of which Rovelli is the protagonist), those on star formation at the beginning of the universe, those on the nature of dark matter, the study of the reality, not yet grasped, of the cosmic radiation passing through us. Research frontiers supported by extraordinary observational technology: satellite telescopes that read the matter of the universe in all the frequency bands in which it is expressed; future large interferometers that will decipher gravitational waves (the real marker of the activity of very distant black holes); particle accelerators that will reproduce the conditions of the early universe, where massive black holes are thought to have formed at the center of galaxies. This science continues to speak the language of Galileo and Einstein and, indeed, feels no need to escape into Eastern mysticism.