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Black-hole complementarity
1993· Theory
SpeculativeA serious idea with no experimental proof yet.
A 1993 proposal that information both escapes and falls into a black hole, with no single observer able to see both.
See it on the Science map →How it works
Leonard Susskind, Lárus Thorlacius and John Uglum, building on Gerard 't Hooft, argued that an outside observer sees information smeared on a hot layer just above the horizon and later carried off in radiation, while someone falling in sees it pass inside smoothly. Copying information is normally forbidden, but since nobody can compare the two copies, no contradiction ever shows up in an experiment.
Why it matters
It was the leading attempt to save both quantum theory and relativity, and forced physicists to ask whether descriptions depend on the observer.
Think of it like
Two appraisals of one building done from different vantage points; each is consistent, and no one can stand in both places at once.
How we know
No experimental test is possible. It is supported by thought experiments and string-theory reasoning. In 2012 the "firewall" argument showed it may be internally inconsistent.
Still a mystery
Does the firewall argument break it? Proposed fixes, such as the 2013 "ER = EPR" idea linking wormholes and entanglement, are unproven.
Connections (2)
▸The black-hole information paradox has a proposed answer in Black-hole complementaritySpeculative
The relationship
Complementarity tries to dissolve the paradox by saying the outside and infalling descriptions are both correct but never compared. Outside, information is absorbed by a hot layer just above the horizon and later radiated out. Inside, it falls through smoothly. Because no single observer can check both versions, quantum theory's ban on copying information is never visibly broken.
How the link was found
Leonard Susskind, Lárus Thorlacius and John Uglum, 1993, building on Gerard 't Hooft's ideas from the late 1980s.
Is it proven?
Not proven or testable. In 2012 Almheiri, Marolf, Polchinski and Sully ("AMPS") argued it leads to a contradiction unless a "firewall" burns infallers at the horizon.
Open questions and mysteries
Is there a firewall? Can complementarity be repaired, for instance by the "ER = EPR" link between entanglement and wormholes?
▸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.