Speaker

Daniel Harlow

Daniel Harlow

Theoretical physicist and Associate Professor of Physics at MIT, working on quantum gravity — the still-unfinished attempt to bring gravity into the quantum framework — with a particular focus on black hole information, holography, and, more recently, quantum cosmology.

Harlow belongs to the generation that reframed quantum gravity around quantum information: instead of quantising a classical field, it studies how spacetime, locality, and the counting of physical states emerge from entanglement and from the algebra of quantum observables. He works largely in tractable toy models — anti-de Sitter space, low dimensions, extra supersymmetry — on the wager that gravity’s universality makes their lessons carry over to the real world. His recent turn is to apply the same machinery to the universe as a whole, treating the cosmos as a quantum system with no outside observer.

Core positions

Harlow reads Hawking’s black hole information paradox as a trilemma — finite entropy, unitarity, locality; keep any two — and sides with the modern resolution that surrenders strict locality, so that spacetime is emergent: position and time are approximate notions that dissolve under operations exponentially complicated in a black hole’s entropy. He regards the gravitational path integral as an oracle that returns correct answers (a black hole’s state count, its unitary evaporation) which one must still work to interpret, and prefers accounts grounded in the underlying quantum degrees of freedom over the path integral taken as the last word.

His most provocative claim is about quantum mechanics itself. Applying holography to a closed universe yields a one-dimensional Hilbert space — a single possible state — which he takes as evidence that textbook quantum mechanics tacitly requires an observer standing outside the system, a crutch unavailable in cosmology. His proposed repair keeps the observer inside the system but subjects them, as a law of nature, to a decohering channel that renders them classical, recovering ordinary effective physics only up to errors of order e^(−S) in the observer’s own entropy. He holds that the collapse of the wave function is subjective — it happens for you when you learn the result — and is explicitly not an Everettian, a point he and Sean Carroll contest at length.

In the wiki