Leonard Susskind Explains Why Reality Is an Illusion

Added: 2026-05-14

[00:00:00][music] >> You think reality is made of matter, particles, atoms, solid things you can touch, things that exist independent of observation, independent of measurement, independent of you.

[00:00:19]But, what if I told you that everything you see, everything you touch, everything you think is solid is actually made of something else entirely.

[00:00:29]Not matter, not energy, information.

[00:00:34]Pure information encoded on the surface of reality itself.

[00:00:38]And if this is true, then the universe you think you live in is fundamentally not what it seems.

[00:00:45]I'm Leonard Susskind and I've spent 50 years thinking about the deepest structure of reality.

[00:00:52]And what physics has discovered in the last few decades is so radical, so strange that most people have no idea this revolution even happened. We've learned that reality at its most fundamental level is not a collection of things. It's a collection of bits.

[00:01:10]Quantum bits of information distributed across the universe in ways that create the illusion of three-dimensional space, of time, of matter.

[00:01:20]The universe is not a stage where information plays out.

[00:01:24]The universe is information.

[00:01:26]The problem started with black holes.

[00:01:30]In the 1970s, Stephen Hawking made a discovery that threw physics into crisis.

[00:01:36]He showed that black holes emit radiation, thermal radiation with a specific temperature. This radiation means black holes evaporate over incredibly long time scales. They radiate away their mass and eventually disappear completely.

[00:01:52]That's strange enough.

[00:01:54]But, here's where the crisis begins.

[00:01:57]When matter falls into a black hole, it carries information.

[00:02:01]The exact quantum state of every particle, every field, every bit of structure in quantum mechanics, information is never destroyed.

[00:02:12]The evolution of quantum states is unitary, reversible in principle.

[00:02:17]This is a fundamental law. Information conservation is as sacred in quantum mechanics as energy conservation.

[00:02:24]But if a black hole evaporates completely through Hawking radiation, and that radiation is purely thermal, random, with no structure, then where did the information go?

[00:02:36]The matter that fell in carried specific information. The Hawking radiation coming out is random noise. The information seems to have been destroyed.

[00:02:45]This is the black hole information paradox.

[00:02:49]And for nearly 40 years, it was an open wound in physics.

[00:02:55]Hawking himself initially argued that information is destroyed in black holes, that quantum mechanics breaks down. Most physicists, myself included, found this unacceptable.

[00:03:09]Quantum mechanics is too successful, too well tested, too fundamental to give up. So, we searched for another solution. And the solution we found is even stranger than the problem.

[00:03:22]It suggests that reality itself is holographic, that the three-dimensional space we think we live in is an illusion.

[00:03:30]That all the information describing everything in a volume of space is actually encoded on the two-dimensional boundary of that volume.

[00:03:39]Like a hologram, where a flat surface contains all the information needed to reconstruct a three-dimensional image.

[00:03:46]This is the holographic principle, and it changes everything. You think reality is made of matter, particles, atoms, solid things you can touch, things that exist independent of observation, independent of measurement, independent of you.

[00:04:04]But what if I told you that everything you see, everything you touch, everything you think is solid is actually made of something else entirely?

[00:04:16]Not matter, not energy, information.

[00:04:20]Pure information encoded on the surface of reality itself.

[00:04:25]And if this is true, then the universe you think you live in is fundamentally not what it seems.

[00:04:32]I'm Leonard Susskind and I've spent 50 years thinking about the deepest structure of reality.

[00:04:37]And what physics has discovered in the last few decades is so radical, so strange that most people have no idea this revolution even happened.

[00:04:48]We've learned that reality at its most fundamental level is not a collection of things. It's a collection of bits.

[00:04:57]Quantum bits of information distributed across the universe in ways that create the illusion of three-dimensional space, of time, of matter. The universe is not a stage where information plays out.

[00:05:12]The universe is information.

[00:05:14]The problem started with black holes. In the 1970s, Stephen Hawking made a discovery that threw physics into crisis. He showed that black holes emit radiation.

[00:05:25]Thermal radiation with a specific temperature. This radiation means black holes evaporate. Over incredibly long time scales, they radiate away their mass and eventually disappear completely.

[00:05:38]That's strange enough, but here's where the crisis begins. When matter falls into a black hole, it carries information.

[00:05:47]The exact quantum state of every particle, every field, every bit of structure. In quantum mechanics, information is never destroyed. The evolution of quantum states is unitary, reversible in principle.

[00:05:58]This is a fundamental law. Information conservation is as sacred in quantum mechanics as energy conservation.

[00:06:06]But, if a black hole evaporates completely through Hawking radiation, and that radiation is purely thermal, random, with no structure, then where did the information go? The matter that fell in carried specific information.

[00:06:21]The Hawking radiation coming out is random noise. The information seems to have been destroyed. This is the black hole information paradox.

[00:06:30]And for nearly 40 years, it was an open wound in physics.

[00:06:35]Hawking himself initially argued that information is destroyed in black holes, that quantum mechanics breaks down. Most physicists, myself included, found this unacceptable.

[00:06:49]Quantum mechanics is too successful, too well tested, too fundamental to give up.

[00:06:55]So, we searched for another solution.

[00:06:58]And the solution we found is even stranger than the problem.

[00:07:01]It suggests that reality itself is holographic, that the three-dimensional space we think we live in is an illusion, that all the information describing everything in a volume of space is actually encoded on the two-dimensional boundary of that volume.

[00:07:20]Like a hologram, where a flat surface contains all the information needed to reconstruct the three-dimensional image. This is the holographic principle, and it changes everything. This brings me to quantum entanglement. Entanglement is a phenomenon where two quantum systems become correlated in ways that cannot be explained by classical physics.

[00:07:43]When particles are entangled, measuring one particle instantaneously affects the other, no matter how far apart they are.

[00:07:52]Einstein called this spooky action at a distance, but it's real.

[00:07:57]It's been confirmed thousands of times.

[00:08:00]And entanglement turns out to be the glue that holds space-time together.

[00:08:05]In 2006, Shinsei Ryu and Tadashi Takayanagi discovered a remarkable formula.

[00:08:13]They showed that the amount of entanglement between two regions on the boundary is precisely related to the geometry of space-time in the bulk. What this means is profound. Entanglement, a quantum information concept, determines space-time geometry. More entanglement means more connected space-time. Less entanglement means space-time is torn apart.

[00:08:36]In a very real sense, space-time is woven from entanglement.

[00:08:41]Mark Van Raamsdonk pushed this further.

[00:08:44]He showed that if you remove entanglement between parts of the boundary theory, the bulk space-time literally tears apart. Entanglement doesn't just correlate with space-time geometry, it creates it. Without entanglement, there is no space-time.

[00:08:59]There's just disconnected bits of information. This is revolutionary.

[00:09:05]For centuries, we thought space and time were the stage on which physics plays out. Einstein showed space-time is dynamical. It curves and bends. But even in Einstein's theory, space-time is fundamental.

[00:09:19]Now, we're saying space-time itself is emergent. It's not fundamental. It arises from quantum information and entanglement patterns. And if space-time is emergent, then so is everything in it.

[00:09:33]Matter, energy, forces, particles, all of these are patterns in the information structure. The universe is not made of stuff.

[00:09:44]It's made of information organizing itself according to quantum mechanical rules.

[00:09:49]Take a black hole again. When you fall into a black hole, from your perspective, you cross the event horizon smoothly. Nothing special happens at the horizon itself.

[00:10:00]But from the perspective of someone outside the black hole, you never cross the horizon. You appear to freeze at the horizon surface.

[00:10:09]Your information spreads out across the horizon and eventually gets emitted in the Hawking radiation. Both descriptions are correct. The three-dimensional description of you falling through the horizon and the two-dimensional description of your information spreading on the horizon are two ways of talking about the same thing.

[00:10:30]The holographic principle tells us the two-dimensional description is complete.

[00:10:35]All the information is on the boundary.

[00:10:37]The interior of the black hole is reconstructed from that boundary information.

[00:10:43]It's emergent. This leads to something called black hole complementarity, an idea I developed in the 1990s.

[00:10:51]The principle says that no single observer can see both descriptions simultaneously.

[00:10:57]An observer falling into the black hole sees the interior. An observer staying outside sees the information on the horizon. These are complementary descriptions that never contradict each other for any single observer.

[00:11:10]Complementarity resolves the information paradox. Information is not lost. It's encoded on the horizon and eventually emitted in Hawking radiation in a scrambled form. The information is preserved. What we've learned from black holes tells us something universal.

[00:11:29]Information is conserved. Information determines physical reality, and information can be encoded in surprising places, on boundaries rather than in volumes.

[00:11:41]Now, let's talk about what information actually is in physics.

[00:11:45]The physicist John Archibald Wheeler coined the phrase "it from bit" to capture this idea.

[00:11:53]Every physical thing, every it, derives its existence from information, from bits of yes or no answers to quantum measurements.

[00:12:03]In quantum mechanics, the state of a system is described by a wave function, but you can't measure the wave function directly. You can only extract partial information through measurements.

[00:12:16]Each measurement gives you one bit of information. The full quantum state of even a simple system requires many bits to describe. When systems interact, information flows between them.

[00:12:29]Entanglement creates correlations that can't be described separately. This is quantum information theory, and it's become one of the most active areas of physics.

[00:12:39]We now understand that quantum entanglement is a resource that can be used for computation, communication, and creating space-time geometry.

[00:12:48]Information is not just something that exists in the universe.

[00:12:51]Information is what the universe is made of.

[00:12:55]If reality is information, where is this information encoded?

[00:13:00]In the holographic principle, the information is on the boundary.

[00:13:05]But what is the boundary made of?

[00:13:07]This is where we reach the limits of current understanding. The boundary is a mathematical construct, the limit as you go to the edge of space-time.

[00:13:16]In our universe, we think there's a similar boundary called the cosmic horizon. Perhaps all the information describing our observable universe is encoded on this cosmic horizon, but we don't know what degrees of freedom live on that horizon.

[00:13:33]Some physicists have speculated that information is the most fundamental thing, that there is no substrate.

[00:13:41]Information is not encoded in something.

[00:13:44]Information is the thing. The universe is self-subsisting information organizing itself. The laws of physics are algorithms, rules for how information updates and correlates.

[00:13:55]This sounds mystical, but it's actually very concrete in quantum mechanics.

[00:14:00]The Schrödinger equation tells you how quantum information evolves. The universe is a quantum computer computing its own evolution.

[00:14:08]This is not a metaphor. This is literally what quantum mechanics says.

[00:14:13]Every interaction is a computation.

[00:14:16]Every measurement is information extraction.

[00:14:19]Every entangled state is a quantum bit of information shared between systems.

[00:14:26]Now, here's where this gets philosophically disturbing. If reality is information, what is doing the observing?

[00:14:34]The observer in quantum mechanics plays a special role. Before measurement, a quantum system exists in a superposition of multiple states.

[00:14:44]Only upon measurement does it collapse to a definite state.

[00:14:49]Different interpretations disagree about what measurement means, but they all agree that measurement extracts information.

[00:14:56]The history of measurements, the record of outcomes, is what constitutes classical reality.

[00:15:03]You experience a classical world because information about quantum states has been extracted, copied into the environment, and into your brain.

[00:15:12]Your conscious experience is the result of information processing. Your brain is detecting, correlating, storing information about the world. In a deep sense, consciousness might be what information integration feels like from the inside.

[00:15:30]This connects to another idea that black holes scramble information maximally.

[00:15:35]When information falls into a black hole, it gets mixed completely. The black hole is the fastest scrambler in nature, and scrambling is universal. Any system that thermalizes scrambles information.

[00:15:48]Your coffee cup scrambles information, the universe scrambles information, entropy increases information becoming scrambled.

[00:15:56]The second law of thermodynamics is fundamentally a statement about information.

[00:16:02]It says information becomes more scrambled over time.

[00:16:06]This is why we can't reverse time.

[00:16:09]The information you'd need to reverse every particle is scrambled throughout the environment. The Big Bang was a state of extremely low entropy.

[00:16:19]The universe started in a highly organized configuration.

[00:16:23]Since then, entropy has been increasing, but locally structures can emerge.

[00:16:31]Galaxies, stars, planets, life, all of these are patterns in the information structure of the universe.

[00:16:41]Temporary patterns in the flow of increasing entropy, and these patterns, including you, are made of information. Your DNA is information. About 750 megabytes encoding instructions for building a human. Your brain contains information, memories, knowledge, personality, your consciousness, your sense of self, all of this is information processing.

[00:17:09]You are a pattern of information that maintains itself by extracting energy from the environment and and entropy.

[00:17:16]When you die, your information structure falls apart. The information doesn't disappear. It becomes scrambled. The organized pattern that was you disperses into the environment. Death is information scrambling. But here's something beautiful.

[00:17:33]While we exist, we process information in ways that matter. We extract meaning.

[00:17:40]We find patterns. We create new information structures.

[00:17:45]We pass information to the next generation.

[00:17:49]The universe through us is becoming aware of itself. We are the universe's way of organizing information to ask questions about information.

[00:18:00]We are information studying information.

[00:18:03]This is what Wheeler meant by it from bit.

[00:18:06]The physical world emerges from information.

[00:18:09]But there's a deeper question. Where do the laws come from?

[00:18:13]Why does information organize according to quantum mechanics? We don't have an answer yet. Some think the laws are arbitrary.

[00:18:21]Others hope for a deeper explanation from pure mathematics, from information theory itself. Maybe the laws of physics are the only consistent way information can organize.

[00:18:33]What we do know is that information is conserved.

[00:18:37]Information determines structure.

[00:18:40]Information creates space-time, and information is what we're made of. This is not philosophy. This is what decades of research have revealed. The universe is not a collection of objects in space.

[00:18:53]The universe is a web of information creating the illusion of space, time, and matter.

[00:19:00]You are not a thing. You are a process.

[00:19:04]An information processing pattern that maintains itself temporarily before dissolving back into the information sea.

[00:19:11]And while exist, you are part of the universe knowing itself.

[00:19:16]Information studying information. This is what physics tells me after 50 years.

[00:19:22]The universe is made of information.

[00:19:26]Everything else is emergent. Reality is not what you see. Reality is the information that creates what you see.

[00:19:33]Welcome to the information age.