The holographic principle: why physicists think space might be an illusion

The holographic principle holds that everything happening inside a region of space can be reconstructed entirely from measurements taken on its boundary surface — meaning the information needed to describe a volume scales with its surface area, not its volume. It sounds absurd, like reading every neuron in a brain by photographing only its outer surface, but it has become one of the most influential ideas in theoretical physics. Its formal backbone, the AdS/CFT correspondence proposed in the late 1990s, is the most-cited body of theoretical physics work of the digital era and yielded the widely accepted resolution to the black hole information paradox: contrary to Hawking’s earlier argument, information is not permanently trapped inside black holes.

The idea is rooted in gravity’s peculiarity. Because mass is always positive — there is no negative mass to cancel it out — the warping of spacetime at a boundary uniquely encodes the arrangement of matter inside, unlike electromagnetism, where opposite charges can produce identical fields and hide the interior. The stronger clue came from black hole thermodynamics: in the 1970s Bekenstein and Hawking found that a black hole’s entropy grows with its surface area rather than its volume. Leonard Susskind (along with Gerard ‘t Hooft and Charles Thorn) took this literally, proposing that a black hole is a hologram whose interior is redundant. Since any region of space can in principle collapse into a black hole, the argument generalizes: ordinary space itself may be holographic.

The interpretation is not settled. Latham Boyle accepts the black hole entropy results but disputes the mystical reading, suggesting physicists are conflating two different quantities — a volume-dependent entropy counting how many particles fit inside, and a separate area-dependent ‘entanglement’ entropy tracking quantum correlations crossing the boundary. On his account the area-scaling is real but far less exotic than ‘space is an illusion.’ The piece frames holography as caught between two descriptions physicists themselves toggle between: rigorous mathematical fact on one hand, and speculative flight of fancy on the other.