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The universe is not matter inside spacetime.
Spacetime is how quantum information organizes itself.

≈ 15 min · 11 chapters

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The GR / QM conflict

For a century, physics has possessed two extraordinarily precise theories.

THE STAGE

General relativity says spacetime is a smooth, continuous fabric. Mass curves it. Curvature dictates motion.

THE ACTOR

Quantum mechanics says everything is granular, discrete, probabilistic. Particles do not exist before measurement.

But when we try to combine them... Yet this is essential to describe a black hole's core or the Big Bang. How do you quantize the actor that is also the stage?

The equations blow up. We get infinities. Uncontrollable ones.

Emergent spacetime

What if the question itself is wrong?

We try to "marry" gravity and quantum mechanics. But that's like asking how to marry temperature and atoms.

Temperature is not fundamental.

It does not exist at the microscopic level. It is a statistical illusion that emerges from the motion of countless molecules.

Spacetime is the same.

Not a fixed stage. Not a fundamental ingredient of the universe.

A macroscopic illusion emerging from quantum information.

WebGL…

Conceptual visualization, a pedagogical metaphor, not a numerical simulation of physics equations.

Control panel

Spacetime emerges from quantum entanglement links between qubits. Distance becomes the inverse of entanglement.

QUBITS: 60LINKS: 0FPS: 60

A paradigm shift

Fifty years of converging clues

1973Bekenstein

Entropy lives on the surface

Bekenstein proposes that a black hole's entropy is proportional to its horizon area, not its volume. The first holographic hint.

1974Hawking

Black holes evaporate

Hawking shows that black holes radiate and fixes the formula S = A/4. The information paradox is born: what happens to what fell in?

1997Maldacena

Holography (AdS/CFT)

A theory with gravity in Anti-de Sitter space is equivalent to a quantum theory without gravity living on its boundary, with one dimension fewer. Gravity behaves like a hologram.

2006Ryu & Takayanagi

Entanglement measures geometry

The entanglement entropy of a boundary region equals the area of a minimal surface in the interior. Entanglement and geometry become two languages for the same reality.

2010Van Raamsdonk

Entanglement stitches space together

Reducing the entanglement between two halves of the boundary pulls the corresponding regions of spacetime apart until they disconnect. Without entanglement, space falls apart.

2010Verlinde

Gravity may be entropic

Verlinde proposes that gravity is not a fundamental force but emerges statistically, like gas pressure. A hypothesis still under debate.

2013Maldacena & Susskind

ER = EPR

Conjecture: two entangled particles would be linked by a microscopic wormhole. The connectivity of space would be made of entanglement.

2015Pastawski, Yoshida, Harlow & Preskill

Spacetime as a code

The holographic correspondence behaves like a quantum error-correcting code: information from the interior is redundantly encoded on the boundary.

2019Penington; Almheiri et al.

The Page curve recovered

By adding entanglement "islands" to the calculation, two teams recover the Page curve: information does seem to escape an evaporating black hole.

What we don't know

Many physicists believe the direction is right. But knowing the direction is not the same as finding the path.

Dynamic equations

We know entanglement generates geometry in static cases. But how does it evolve to produce an expanding, dynamic universe?

Fundamental bits

If the universe is made of information, what are the fundamental degrees of freedom? Qubits? Tensor network spins? Something else?

De Sitter vs Anti-de Sitter

Everything we can do mathematically works in Anti-de Sitter space (negative curvature). Our universe is de Sitter (positive curvature).

Experimentally testable prediction

Until we extract a measurable prediction distinct from general relativity, it remains an intuition, however beautiful.

Further reading

Foundational papers and recommended sources

All sources and method →

Glossary

Key terms in holographic physics

Bekenstein-Hawking entropy
S = A/4 in Planck units: a black hole's entropy is proportional to its horizon area, not its volume. It is the first hint of the holographic principle.
Page curve
The expected evolution of the entropy of Hawking radiation if information is preserved: it rises, then falls after the "Page time", once the black hole has lost about half its entropy. 2019 calculations using "islands" reproduced it.
Entanglement
Quantum correlation between two systems so strong they can no longer be described independently, even at a distance.
Decoherence
Loss of quantum superposition through interaction with the environment: quantum information becomes classical.
AdS/CFT
Holographic correspondence: a gravitational theory in Anti-de Sitter space is equivalent to a non-gravitational quantum theory on its boundary.
ER = EPR
Conjecture linking Einstein-Rosen wormholes (ER) to EPR entangled pairs: entanglement would be a geometric shortcut.
Holographic principle
Information in a volume of space can be encoded on its boundary, like a 2D hologram encoding a 3D scene.
De Sitter / Anti-de Sitter
Two cosmological curvatures: de Sitter (positive, our accelerating universe) and Anti-de Sitter (negative, where holography is best understood).

See all 16 definitions →

Artistic illustration

[ singularity ]

Beyond the horizon,

information is not lost.

Black holes are not bottomless pits. They encode everything that falls in on their surface, a holographic projection where spacetime emerges from entanglement.

Explore the horizons

[ observed ]

They are no longer just equations: we have photographed and heard them.

In 2015, LIGO caught the shiver of spacetime from two merging black holes. In 2019 and 2022, the Event Horizon Telescope imaged their shadow.

Event Horizon Telescope image of M87*: a glowing orange ring, brighter at the bottom, around a dark disk.Real image

M87*, released 10 April 2019. A 42-microarcsecond ring around a 6.5-billion-solar-mass black hole 55 million light-years away.

Credit: EHT Collaboration · CC BY 4.0

Event Horizon Telescope image of Sgr A*: a glowing ring with three bright spots around a dark centre.Real image

Sgr A*, released 12 May 2022. The black hole at the centre of the Milky Way: about 4.3 million solar masses, 27,000 light-years away.

Credit: EHT Collaboration · CC BY 4.0

14 September 2015: black holes of 36 and 29 solar masses merge 1.3 billion light-years away.

Three solar masses are turned into gravitational waves in a fraction of a second. The signal, GW150914, earned Rainer Weiss, Barry Barish and Kip Thorne the 2017 Nobel Prize.

The GW150914 chirp, synthesized
Synthesized sound

Sound computed in your browser from a simplified model: a Newtonian inspiral for a chirp mass of 30 solar masses, then the damped ringing of the final black hole. It is not LIGO's recording, but it reproduces its shape: a rise in frequency and loudness from 35 to about 150 Hz in 0.2 seconds.

1,560 ly
Gaia BH1, the nearest known black hole (2022)
33 M☉
Gaia BH3, the most massive stellar black hole in the Milky Way (2024)
S = A/4
A black hole's information scales with its horizon area
Understand the observed black holes →All about gravitational waves →To the epilogue ↓

[ go further ]

Explore black holes

Pages to understand in depth, tools to play with orders of magnitude, and resources for the classroom.

Understand

Interactive tools

Reference