Why Physicists Think Space May Have a Holographic Description

Quanta staff writer Charlie Wood explores the holographic principle, the idea that everything happening inside a region of space might be completely describable by information associated with its boundary. One of the earliest clues came from black holes, where Jacob Bekenstein and Stephen Hawking found that entropy scales with surface area rather than volume.

An even stronger result emerged in the late 1990s. Physicists discovered that, in a specially shaped theoretical universe, a world containing gravity can be mathematically equivalent to a quantum theory living on its lower-dimensional boundary. The two descriptions look radically different, yet encode the same physics.

That does not prove our own universe is holographic. The geometry used in this correspondence differs from the expanding universe we actually inhabit, and physicists disagree about how far the idea can be generalized. Black holes provide additional evidence that the relationship between volume and boundary may be more fundamental, but a complete holographic theory of our universe does not yet exist.

Wood ultimately focuses on what holography might mean for reality itself. Space could emerge from a more fundamental layer of quantum information, the familiar three-dimensional world could be fundamental instead, or both descriptions could be approximations of a deeper theory physicists have not yet found. The important result is not that we literally live inside a projected image, but that modern physics has discovered cases where seemingly different versions of reality can contain exactly the same information.