The holographic principle emerged from studies of black hole thermodynamics. In the 1970s, Jacob Bekenstein and Stephen Hawking calculated that a black hole’s entropy—a measure of its internal disorder—scales with the surface area of its event horizon, not with its volume. This was unexpected because entropy normally counts how much stuff fits inside an object. As physicist Leonard Susskind later noted, the result suggested that everything that can be known about the interior of a black hole might be determined by measurements on its horizon alone, leading to the idea that the three‑dimensional black hole is a hologram encoded in two dimensions.
This image supports the article's explanation that black hole entropy scales with surface area, suggesting the three-dimensional black hole is a hologram encoded in two dimensions.
The principle gained a rigorous mathematical framework with the AdS/CFT correspondence discovered in the late 1990s. Researchers showed that a theory of gravity in anti‑de Sitter (AdS) space—a negatively curved spacetime that can be pictured as a finite snow globe—is exactly equivalent to a conformal field theory (CFT) living on its boundary. This duality means that every event in the AdS interior has a precise counterpart in the CFT surface world, and vice versa. As Brian Swingle of Brandeis University explained, gravity and quantum mechanics are not opposing forces but are intertwined, with one emerging from the other in this setting.
Whether this holographic description applies to our own universe remains uncertain. Our cosmos exhibits accelerated expansion, resembling a de Sitter space rather than AdS space, and de Sitter spacetime lacks a boundary surface where a hologram could be projected. Physicist Latham Boyle of the University of Edinburgh has argued that the entropy increase with area observed in black holes may instead reflect entanglement entropy between interior and exterior particles, not a true holographic encoding. Proponents counter that an observer inside AdS space cannot easily detect its curvature, so the holographic principles might hold approximately for our universe; Leonard Susskind suggests that if holography holds for the spacetime physicists understand best, it is unlikely that reality works in a fundamentally different way. Consequently, the holographic nature of space remains a compelling but unproven idea that challenges intuitive notions of dimensionality.