Leonard Susskind

Leonard Susskind was born in 1940 in the South Bronx, the son of a plumber, and worked as a plumber himself before going to college. He took a physics degree at the City College of New York and a doctorate at Cornell in 1965. His early career coincided with the birth of string theory: in 1969–70, independently of Yoichiro Nambu and Holger Bech Nielsen, he interpreted the Veneziano scattering amplitude as describing a vibrating relativistic string, making him one of the three discoverers of the idea that elementary particles are extended one-dimensional objects.

Over the following decades Susskind contributed foundational ideas across particle physics and gravity: technicolor models, the Kogut–Susskind lattice formulation of quark fields, and the realization that the entropy of a black hole points to a radical economy of information. In 1993 he, with Gerard 't Hooft, proposed the holographic principle — the claim that the physics inside a region of space can be fully encoded on its boundary, with no more than one bit per Planck area. It became one of the organizing ideas of modern theoretical physics and the conceptual backbone of the later resolution of the information paradox.

Susskind was Stephen Hawking's most relentless opponent in what he later named the 'black hole war.' Convinced that Hawking's 1976 claim of information loss would, if true, destroy quantum mechanics, he spent two decades developing the counter-case: black-hole complementarity (with 't Hooft and Thorlacius), the idea that an infalling and an external observer give complementary, non-contradictory accounts of the same physics, and the holographic encoding of the interior on the horizon. His 2008 popular book *The Black Hole War* is the standard insider account of the dispute.

Since 1979 Susskind has been the Felix Bloch Professor of Theoretical Physics at Stanford University, where he founded the Stanford Institute for Theoretical Physics. In later years he turned to the relationship between quantum entanglement, computational complexity, and the geometry of spacetime — the 'ER = EPR' conjecture with Juan Maldacena and the 'complexity = volume' program — extending the holographic ideas that grew out of his fight over black holes.