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Leonard Susskind
1993· Person
ProvenTested many times; part of working physics.
Leonard Susskind (born 1940) is an American theoretical physicist at Stanford, a founder of string theory and of holography.
See it on the Science map →How it works
A former plumber from the Bronx, Susskind thinks in pictures and bold leaps. Around 1969-70 he saw that a formula for the strong force described vibrating strings, an early root of string theory. In the 1990s he fought Stephen Hawking's claim that black holes destroy information, proposing black-hole complementarity (1993) and building out the holographic principle (1995). In 2003 he pushed the string "landscape" of countless possible universes, and in 2013 co-proposed ER = EPR with Maldacena.
Why it matters
He was a key voice in convincing physicists that information is never lost, even in black holes. That view now shapes most research on quantum gravity.
How the work held up
Hawking conceded the information bet in 2004. AdS/CFT (1997) and Page-curve calculations (2019) supported Susskind's side mathematically. None of his main ideas has yet been tested by experiment.
Still a mystery
Whether string theory and his landscape describe our actual universe is unproven, and critics say the landscape may never be testable.
Connections (4)
▸Leonard Susskind proposed Black-hole complementaritySpeculative
The relationship
Susskind proposed that two descriptions of a black hole are both right. Someone falling in passes the horizon unharmed and carries information inside. A distant observer sees the same information smeared on the horizon and later leaked out in radiation. Since no one can see both versions and compare, there is no contradiction and no duplicated information.
How the link was found
Leonard Susskind, Lárus Thorlacius and John Uglum published it in 1993, building on earlier ideas of Gerard 't Hooft about the horizon.
Is it proven?
It is consistent in thought experiments and fits AdS/CFT's message that information survives. It is not tested. In 2012 the AMPS "firewall" paper showed it may conflict with basic quantum rules.
Open questions and mysteries
Does the infalling observer really feel nothing at the horizon, or hit a firewall? ER = EPR and later Page-curve work offer partial answers.
▸Leonard Susskind co-founded String theorySpeculative
The relationship
In 1968 Gabriele Veneziano found a formula that fit how strongly interacting particles scatter. Susskind realized the formula described tiny vibrating strings rather than points. That reinterpretation turned a curve-fitting formula into a physical picture, which later grew into string theory as a candidate theory of everything.
How the link was found
Leonard Susskind, and independently Yoichiro Nambu and Holger Bech Nielsen, around 1969-70. Susskind's first paper was initially rejected by a journal.
Is it proven?
The historical link is documented in the original papers. String theory itself has never been confirmed by experiment.
Open questions and mysteries
Whether string theory describes nature remains open. It ultimately failed for the strong force but survived as a candidate theory of gravity.
▸Leonard Susskind developed The holographic principleSpeculative
The relationship
Susskind took 't Hooft's counting argument and showed how string theory could make it work, presenting the world as a hologram. His paper gave the idea its name and momentum, connecting it to his own black-hole complementarity and to string theory's way of storing information.
How the link was found
Leonard Susskind, in "The World as a Hologram" (1995). Willy Fischler and Susskind (1998) and Raphael Bousso (1999) extended it to expanding universes.
Is it proven?
AdS/CFT appeared two years later and matched it precisely, which greatly raised confidence. It remains unconfirmed by experiment.
Open questions and mysteries
Making holography work for an expanding universe like ours, rather than model universes, is still unsolved.
▸Leonard Susskind proposed with Maldacena ER = EPR: entanglement may build spaceSpeculative
The relationship
Susskind brought the problem: the 2012 firewall paradox suggested black-hole complementarity might fail. ER = EPR offered an escape: radiation leaving a black hole stays connected to the interior through wormholes, so information is not duplicated and no firewall is needed. Susskind has since promoted it as a sign that quantum mechanics and gravity are one subject.
How the link was found
Leonard Susskind with Juan Maldacena, 2013, responding to the firewall paper by Almheiri, Marolf, Polchinski and Sully (2012).
Is it proven?
Mathematically consistent in models; not tested. Later Page-curve work (2019) fits its spirit.
Open questions and mysteries
Whether it fully resolves the firewall paradox is still debated.