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When Janna Levin speaks about black holes, she doesn't just describe exotic objects in space—she reveals portals into the deepest mysteries of existence itself. A theoretical physicist and cosmologist at Columbia University, Levin has spent her career exploring black holes, extra dimensions, and gravitational waves, while also bridging the worlds of science and culture through her acclaimed books and work at Brooklyn's Pioneer Works. In a recent conversation with Lex Fridman, she offered profound insights into the nature of reality, from the emptiness that defines black holes to the fabric of spacetime itself.
Key Takeaways
- Black holes are fundamentally "nothing"—not dense objects but regions of spacetime where the normal rules break down and space and time can switch places
- The formation of black holes requires understanding both Einstein's general relativity and the nuclear physics of stellar death, connecting cosmic and quantum scales
- Gravitational waves represent a completely new way of observing the universe—not through light but through the actual ringing of spacetime itself
- The black hole information paradox reveals deep tensions between quantum mechanics and general relativity, potentially pointing toward a quantum origin of spacetime
- Extra dimensions may exist as hidden aspects of reality, possibly explaining dark matter and dark energy while offering new possibilities for alien communication
- The detection of gravitational waves by LIGO represents one of humanity's greatest engineering achievements, measuring distortions smaller than 1/10,000th of a proton
- Science and art share fundamental connections in their exploration of pattern, beauty, and the human experience of discovering truth
Black Holes: The Profound Emptiness of Everything
Most people imagine black holes as incredibly dense objects—collapsed stars so massive that not even light can escape. But Levin offers a more profound and counterintuitive perspective: "Black holes are nothing. They're no thing." This isn't just semantic precision; it represents a fundamental shift in how we understand these cosmic phenomena.
When Karl Schwarzschild first solved Einstein's equations in 1916—remarkably, while serving on the Eastern Front during World War I—he created what was essentially a thought experiment. "Imagine I crush all the mass of a star to a point," was his premise. "Don't ask how that's done because that's really absurd, but let's just pretend." What emerged from this mathematical exercise was the concept of an event horizon: a boundary in spacetime beyond which not even light can escape.
The crucial insight is that the event horizon itself is empty space. "If you go up to the event horizon, it's an empty region of spacetime," Levin explains. "It's more of a place than it is a thing." The black hole isn't the collapsed star—that matter has fallen through the horizon and disappeared from our observable universe. What remains is a demarcation in spacetime itself, a one-way membrane that separates cause and effect.
This emptiness reveals something profound about the nature of reality. Black holes are described entirely by just three properties: mass, electric charge, and spin. Unlike every other macroscopic object in the universe, they have no other distinguishing features. "You can't be like, 'Oh, that one's mine. I recognize it. It has this little feature,'" Levin notes. "They're featureless." In this sense, they're more like fundamental particles than astronomical objects—perfect, idealized entities that exist at the intersection of physics and mathematics.
The Stellar Forge: How Nature Creates the Impossible
While Einstein found black holes mathematically fascinating, he doubted nature would actually form them. It took the work of J. Robert Oppenheimer—better known as the father of the atomic bomb—to show how stellar death could create these extreme objects. In a prescient 1939 paper published the same day Nazi Germany invaded Poland, Oppenheimer and his student predicted that sufficiently massive stars would inevitably collapse into black holes.
The physics of stellar collapse reveals the universe's most dramatic transformation. Massive stars—perhaps 20 or 30 times the mass of our sun—spend their lives as ongoing thermonuclear explosions, fusing lighter elements into heavier ones. This process creates the delicate balance that keeps stars shining: the outward pressure of nuclear fusion fighting against the inward pull of gravity.
But stars are mortal. Eventually, they reach iron in their cores, and iron represents a dead end for fusion—it requires more energy to fuse than it releases. Suddenly, the star's nuclear furnace shuts down. Gravity wins. The collapse is catastrophic and incredibly rapid. In moments, something larger than our solar system shrinks to the size of a city.
What happens next depends on the final mass. If the stellar core is less than about three times the mass of our sun, it becomes a neutron star—an exotic object where electrons and protons are crushed together into a giant atomic nucleus. But if it's heavier, nothing can stop the collapse. The star forms an event horizon and disappears from the universe, leaving behind only its gravitational influence.
This process reveals a beautiful paradox. The star doesn't sit at the event horizon—it can't, because space and time become so distorted that the normal rules no longer apply. Instead, the star continues falling, leaving the event horizon behind like a gravitational ghost. As John Wheeler poetically described it, "The star like the Cheshire cat fades from view. One leaves behind only its grin, the other only its gravitational attraction."
When Space and Time Trade Places
Perhaps the most mind-bending aspect of black holes is what happens to space and time near the event horizon. Levin describes this as a rotation in spacetime itself: "As you approach the black hole, it's as though you're rotating in spacetime." This isn't just a metaphor—it's a precise description of how the geometry of reality changes.
From the outside, we observe a spherical shadow cast against the cosmic background. We naturally think of the center as a location in space. But for someone falling through the event horizon, space and time literally exchange roles. The singularity at the "center" isn't a place—it's a moment in time, specifically a moment in the future that cannot be avoided.
"You can no more avoid the singularity than you can avoid time coming your way," Levin explains. Once inside the event horizon, all possible paths lead inexorably toward the singularity. You could fire your rockets, try to turn around, attempt any desperate maneuver—but the singularity remains in your future, approaching with the inevitability of tomorrow.
This exchange of space and time creates one of general relativity's most profound paradoxes. From outside the black hole, time dilation becomes so extreme that a falling astronaut appears to slow down and eventually freeze at the horizon, their image redshifted into darkness. But from the astronaut's perspective, they sail through the horizon in normal time, perhaps not even realizing they've crossed the point of no return.
The experience might not even be unpleasant—at least initially. For supermassive black holes, the tidal forces at the horizon are gentle. The falling astronaut might notice that the universe outside appears increasingly bright as light from the entire history of the cosmos blue-shifts and focuses around them. As Levin puts it with characteristic wit, "It's like a near-death experience. You see the light at the end of the tunnel. Except it's definitely a total death experience."
LIGO: Listening to the Universe's Deepest Bass Notes
While black holes themselves emit no light, they can create gravitational waves—ripples in spacetime itself that carry information across cosmic distances. These waves represent an entirely new form of astronomy, one that doesn't rely on electromagnetic radiation but on distortions in the fabric of reality.
The physics is elegant yet extreme. When two black holes orbit each other, they create waves in spacetime much like moving objects create waves in water. But these aren't waves in some medium—they're waves in the medium of existence itself. As the black holes spiral inward, they accelerate, creating stronger waves that carry away energy. Eventually, they merge in a cosmic crescendo that can briefly outshine all the stars in the observable universe—not in light, but in gravitational wave energy.
LIGO's achievement in detecting these waves represents one of humanity's most remarkable engineering accomplishments. The detector consists of two four-kilometer arms arranged in an L-shape, with laser beams precisely measuring the distance between mirrors at each end. When a gravitational wave passes through, it stretches space in one direction while compressing it in the perpendicular direction.
The sensitivity required is almost incomprehensible. LIGO can detect changes in the length of its four-kilometer arms that are smaller than 1/10,000th the width of a proton. "It's an insane achievement," Levin marvels. "I honestly can't believe they succeeded."
The project required fifty years of development, with scientists who began work in their thirties and forties finally seeing success in their eighties. When the first detection occurred on September 14, 2015, it happened to be the centenary year of Einstein's general relativity—a cosmic coincidence that seemed almost too perfect.
But perhaps most remarkably, the gravitational wave signal began its journey to Earth over a billion years ago, before multicellular life had evolved on our planet. "Just imagine this from a distant view, this collision course," Levin reflects. "When Einstein in 1915 wrote down the general theory of relativity, it was on its way here. It was almost here."
The Information Paradox: When Physics Breaks Down
Black holes don't just challenge our understanding of space and time—they create a fundamental crisis in physics through what's known as the information paradox. This stems from Stephen Hawking's discovery that black holes aren't completely black; they emit radiation due to quantum effects near the event horizon.
The mechanism involves virtual particle pairs that constantly pop in and out of existence in empty space. Near a black hole's event horizon, these pairs can be separated, with one particle falling in while the other escapes. From the outside, this appears as though the black hole is slowly evaporating, emitting what's now called Hawking radiation.
The problem arises because this radiation appears to be completely thermal—essentially random heat with no information content. If black holes eventually evaporate completely, as Hawking's calculations suggest they must, then all the information that fell into them would be permanently lost. This violates one of quantum mechanics' most fundamental principles: information must be conserved.
"Quantum mechanics was built to preserve information," Levin emphasizes. "It's one of the sacred principles, as sacred as conservation of energy." The conflict between general relativity's prediction of information loss and quantum mechanics' requirement of information conservation has driven decades of research and heated debate among physicists.
Various solutions have been proposed, from "firewalls" that incinerate anything crossing the event horizon to "fuzzballs" that eliminate the horizon entirely. But Levin finds the most promising resolution in ideas connecting quantum entanglement to the geometry of spacetime itself.
ER = EPR: When Wormholes Meet Quantum Mechanics
One of the most intriguing potential resolutions to the information paradox comes from a surprising connection between Einstein-Rosen bridges (wormholes) and quantum entanglement. The idea, known as ER = EPR, suggests that entangled particles are connected by microscopic wormholes.
"If I look at the event horizon very closely," Levin explains, "I will see that it's actually sewn from these quantum wormholes, like embroidered." This isn't just speculation—it emerges from serious attempts to understand how information might escape from black holes without violating the fundamental principles of quantum mechanics.
The implications are staggering. If quantum entanglement is physically realized through tiny wormholes, then the fabric of spacetime itself might emerge from quantum mechanical phenomena. Rather than trying to quantize gravity, perhaps gravity is quantum mechanics, just at a scale we don't normally perceive.
This represents a complete inversion of how we normally think about physics. Instead of spacetime being fundamental with quantum mechanics operating within it, spacetime itself might be an emergent property of quantum entanglement. "Maybe it's just quantum mechanics all the way down," Levin suggests. "Quantum threads."
Extra Dimensions and Hidden Realities
Beyond the four dimensions we experience directly—three of space and one of time—physics suggests our universe might contain additional spatial dimensions hidden from direct observation. These extra dimensions aren't science fiction; they're mathematical necessities in string theory and potential explanations for some of the universe's deepest mysteries.
The simplest models propose that extra dimensions are "compactified"—curled up so tightly that we can't perceive them directly. But Levin explores more exotic possibilities, including the idea that we might live on a three-dimensional "brane" (membrane) embedded in a higher-dimensional space.
If multiple branes exist in this higher-dimensional realm, it raises fascinating questions about other forms of life. "Is it possible that there's other intelligent alien civilizations out there that are operating on a different membrane?" The physics suggests it's mathematically possible, and if nature can do something, perhaps she tries it.
Communication between branes would require particles or forces that can travel through the higher-dimensional "bulk." Gravity appears to be one such force, leading to the intriguing possibility of gravitational communication systems. "I could send gravitational waves through the bulk," Levin notes, though she acknowledges the enormous technical challenges: "Sending gravitational waves is very expensive."
The Alien Question: Life, Intelligence, and Cosmic Loneliness
The question of alien life fascinates Levin, particularly given the astronomical numbers involved. The Milky Way alone contains hundreds of billions of stars, and we now know that planets are common—perhaps more common than stars themselves. "It becomes impossible to imagine that life was not sparked somewhere else," she observes.
Yet we see no clear evidence of advanced civilizations. This absence puzzles Levin, who notes that nature appears to be an enthusiastic experimenter. Life on Earth emerged quickly after conditions became suitable, suggesting the process might be relatively easy to start. But the progression from simple life to technological civilization involves numerous difficult steps.
Levin points to the long delay between the emergence of single-celled life and multicellular organisms as potentially crucial. "It took a really long time to become multicellular," she notes. "That's weird." This transition required solving fundamental problems of energy distribution and cellular cooperation—challenges that might prove insurmountable for most evolutionary lineages.
But perhaps our assumptions about alien intelligence are too narrow. Levin suggests we might be biased toward imagining creatures like ourselves—technologically oriented, socially organized, and intent on manipulating their environment. Other forms of intelligence might be more contemplative, less expansionist, or organized around completely different principles.
"I think we have to be way more imaginative if we're going to really take seriously life in the universe," she argues. Jellyfish have survived for hundreds of millions of years without centralized brains or hearts, some showing evidence of immortality. Such radically different organizations of life might not prioritize space travel or radio communication.
The Human Story: Science, Art, and Cultural Creation
Throughout her scientific career, Levin has maintained a parallel commitment to understanding science as a fundamentally human endeavor. Her books explore not just the physics of black holes or the detection of gravitational waves, but the people behind these discoveries—their struggles, insights, and very human motivations.
This perspective informs her work at Pioneer Works, a Brooklyn-based cultural center where artists and scientists collaborate on projects that blur traditional boundaries. "I don't think of myself as doing outreach or education," she explains. "I'm doing culture."
The connection between science and art runs deeper than mere communication. Both involve pattern recognition, aesthetic judgment, and the search for meaning within complexity. Great scientists often possess artistic sensibilities, while artists increasingly engage with scientific concepts to explore fundamental questions about existence.
Levin's own reading preferences reveal this integration. She gravitates toward literary fiction that incorporates scientific thinking—authors like Kazuo Ishiguro, whose "Never Let Me Go" explores profound questions about consciousness and identity through a science fiction premise, or Cormac McCarthy, whose "The Road" uses scientific catastrophe to examine the deepest human connections.
Gödel and Turing: The Limits of Knowledge
In her book "A Madman Dreams of Turing Machines," Levin explores the connections between Kurt Gödel and Alan Turing, two intellectual giants whose work revealed fundamental limitations in formal systems of knowledge. Their insights resonate with contemporary physics, where black holes and quantum mechanics challenge our ability to construct complete, consistent theories of reality.
Gödel's incompleteness theorems demonstrated that even mathematics contains true statements that cannot be proven within the system itself. Turing's work on computability showed that certain numbers exist but cannot be calculated by any algorithm. Both results point to inherent limits in what formal reasoning can achieve.
These limitations parallel the challenges facing physics today. The information paradox might be undecidable within our current theoretical frameworks. The nature of quantum measurement might be fundamentally incomputable. Dark matter and dark energy might represent aspects of reality that lie beyond the reach of current scientific methods.
Yet rather than finding these limitations discouraging, Levin sees them as part of the profound beauty of existence. "There's something that eludes you," she notes about understanding the lives of Gödel and Turing. "And I felt like that's kind of fundamental to the mathematics—the incompleteness, the undecidable, the uncomputable."
Time, Impermanence, and Cosmic Perspective
One of the most sobering aspects of cosmology is its ultimate timeline. Current understanding suggests that the universe will eventually reach a state of maximum entropy, where no further complex processes can occur. All the Nobel prizes, mathematical proofs, conversations, and ideas that seem so important to us will eventually be erased.
"That's a tough thought," Levin acknowledges. "But I think there's a way in which we can come to terms with that that's kind of poetic. You build something in the sand and then you erase it."
This cosmic perspective doesn't diminish the importance of human endeavor—rather, it emphasizes the precious nature of our brief moment of consciousness in an vast and largely unconscious universe. We are patterns of complexity that have emerged temporarily from simpler components, capable of understanding and appreciating the very forces that created us.
The knowledge that everything is temporary makes each discovery, each moment of understanding, each human connection more valuable, not less. Like drawing something beautiful in sand before the tide comes in, our scientific and artistic achievements gain meaning precisely because they are not eternal.
The Poetry of Physics
Levin's approach to physics embodies a fundamentally poetic sensibility. She finds beauty in empty spacetime, music in gravitational waves, and profound meaning in mathematical equations that describe the behavior of matter and energy across cosmic scales. This isn't mere metaphor—it reflects a deep truth about the nature of scientific discovery.
The best physics, like the best poetry, reveals unexpected connections between apparently disparate phenomena. Einstein's realization that gravity and acceleration are equivalent led to general relativity. Hawking's application of quantum mechanics to black holes revealed deep connections between thermodynamics, information theory, and the nature of spacetime itself.
These insights emerge not just from calculation but from a kind of aesthetic intuition—a sense for which ideas are beautiful enough to be true. As Levin notes about the scientists she most admires, "They never lie to themselves that they understand something that they don't understand."
This intellectual honesty, combined with an appreciation for beauty and connection, drives the ongoing human quest to understand our universe. Whether exploring black holes, detecting gravitational waves, or searching for alien intelligence, we are fundamentally seeking to understand our place in the cosmic story.
The questions Levin explores—about the nature of space and time, the origin of complexity, the possibility of other intelligence—are among the deepest that humans can ask. They connect physics to philosophy, cosmology to consciousness, and scientific discovery to the fundamental human desire to understand and create meaning.
In the end, perhaps that's what makes black holes such compelling objects of study. They represent the ultimate frontier where our understanding breaks down, where the familiar laws of physics encounter their limits, and where new insights about the nature of reality might emerge. Like the event horizons they study, scientists like Levin operate at the boundary between the known and unknowable, pushing forward into territory where no maps exist and the only guide is the beauty and consistency of mathematical truth.
As we stand at the threshold of new discoveries—about gravitational waves, quantum gravity, and perhaps even the detection of life elsewhere in the universe—Levin's work reminds us that science is ultimately a human endeavor, driven by curiosity, sustained by wonder, and enriched by the same aesthetic sense that creates art, music, and literature. The universe may be vast and largely empty, but the human capacity to understand and appreciate it fills that emptiness with meaning.
