You Can Look Inside a Black Hole. I’ll Show You How.
How do we learn something new, something we do not yet know?
One way, of course, is through experience. This is why the young depart and travel. Another is thanks to someone else, who might have traveled for us. What they have learned comes to us as a story, a lesson at school, a Wikipedia entry, a book. Aristotle and Theophrastus went to the island of Lesbos; they observed the minute movements of fish, mollusks, birds, mammals and plants; and they wrote it all down, opening up for us the world of biology.
Instruments allow us to see even farther. Galileo pointed a telescope at the heavens and saw things people wouldn’t have believed, opening our eyes to the unending vastness of astronomy. Physicists use spectrometers to analyze the light emitted by elements and collect data on the atoms, opening the door to the quantum world.
But what about the things we can’t see at all? How do we learn about the parts of our universe that we cannot — even with the most powerful technology — observe?
I study black holes. We see them in the sky today, thanks to spectacular telescopes, but we only see the exterior. We see matter that spirals furiously, before plunging into them. What’s deep inside? What would we see if we entered a black hole and, resisting the crushing forces, fell all the way down?
Current science has no answer to this question. Einstein’s theory predicts the end of time down there, but the hole’s inner regions are dominated by quantum aspects of space and time, and these are not taken into account by Einstein’s theory.
How can we learn about a place we can neither travel to nor see?
To travel to places that we cannot reach physically, we need more than technology, logic or mathematics. We need imagination.
History has many examples of scientific discoveries that came about through the difficult and subtle art of changing perspective.
Anaximander is the ancient Greek thinker who figured out that the sky is not just above us; it also continues under our feet, and the Earth is like a stone floating in the middle of the void. This is the first and maybe the greatest of the cosmological revolutions. He had the courage to imagine what the Earth would look like from an immense height: a spectacular change of perspective. In this way he could intuit how the planet Earth would much later appear to Neil Armstrong and Buzz Aldrin as they looked up at it from the moon.
Anaximander is also credited as the first person to design a geographical map. Today, maps are familiar, but for millenniums of civilization, travel and trade, no one had thought to render an area of land as it would look if we could fly higher than eagles. To identify with an eagle, to wonder what it would see from such a great height — this was an entirely new perspective.
A very good ancient calculation of the distance to the moon, attributed to Hipparchus, the greatest astronomer of the ancient world, is based on a refined geometric argument that starts with the question “What would I see if I went to the tip of the Earth’s shadow cone?” Hipparchus imagined himself down there, thousands of miles from the Earth, in interplanetary space, looking back and watching the Earth exactly cover the sun. Again, he was seeing with the mind’s eye.
Copernicus looked at the solar system as you would see it from the sun. Johannes Kepler wrote “The Dream,” in which the narrator says he flew to the moon with his mother, and describes how the sky looks from there, with a spinning Earth staying still in the sky. Einstein wondered what he would see if he could ride a ray of light.
How could these people see from a place they had not been to? Anaximander did not soar with eagles, Kepler did not fly to the moon on a broomstick and Einstein did not ride a ray of light. How can we see from somewhere that we cannot actually reach?
I think that the answer is to grope for a delicate balance — a balance between how much of our previously accrued learning we take with us and how much we leave at home, freeing ourselves to reconsider what we think we know. On the one hand, what we carry with us allows us to know what to expect. To know what to expect in the black hole, we can use the equations of Einstein, which predict its geometry. Einstein used the equations of James Clerk Maxwell, which describe how light behaves. Kepler used Copernicus’s book, “On the Revolutions of the Celestial Spheres.” These are the maps, the rules, the generalities that we trust in because they have worked so well. And yet, we know that we must leave something behind.
Anaximander left at home the idea that all things fall in the same direction: For the Earth itself not to fall, falling must be different than what we thought. Kepler left at home the idea that things move in circles, which seems so natural. Einstein left behind the idea that all clocks tick in tune with each other, which still seems obvious to many of us, and yet is wrong. If we leave too many things at home, we lack the tools needed to forge ahead; if we take too many, we fail to find the paths to new understanding. There are no recipes for success. There is only trial and error. Trying and trying again.
This is what we do, the long study and the great love that is scientific inquiry. We combine and recombine in different ways what we know, looking for an arrangement that clarifies something. We leave out pieces that previously seemed essential, if they get in the way. We take risks, albeit calculated ones. We linger at the border of our knowledge. We familiarize ourselves with it, and we spend a long time there, walking back and forth along its length, searching for the gap. We try out new combinations. New concepts.
I think that this is also how the best art works. Science and art are both concerned with the continual reorganization of our conceptual space, of what we call meaning. What happens when we react to a work of art is not happening in the art object itself, of course — still less in some unphysical “world of the spirit.” It lies in the complexity of our brain, in the kaleidoscopic network of analogical relationships with which our neurons weave what we call meaning.
We are involved, engaged — for this takes us out of our habitual sleepwalking, reconnecting us with the joy of seeing something anew in the world.
It is the same joy that science gives us. The light in a Johannes Vermeer painting opens our eyes to a resonance of light in the world that we had not previously been able to seize; a fragment of a poem by Sappho opens up a world in which to rethink desire; one of Anish Kapoor’s voids of pure black disorients us, like the black holes of general relativity. And like the latter, it suggests that there are other ways of conceptualizing the impalpable fabric of reality.
Between observation and understanding, the road can be long. Copernicus and Einstein, for instance, obtained their momentous results based on observations that had been well known in the past — in the case of Copernicus, for more than a millennium. It is the capacity to change the organization of our thoughts that allows us to make the leap.
So how can we reconceptualize reality in order to understand what lies at the bottom of a black hole? I have dedicated my career and my life to the search.
Einstein once said, “The most beautiful thing we can experience is the mysterious. It is the source of all true art and science.” And black holes are among the greatest scientific mysteries of our universe.
Contained within them is an understanding not only of the laws of physics, but of time, space, the universe and the nature of reality. Understanding them requires pushing the limits of imagination. It requires a leap of creative faith. We may already possess everything we need to unlock this greatest of mysteries.
Carlo Rovelli is an Italian physicist and the author of the upcoming book “White Holes,” from which this essay is adapted..
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