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Stephen Hawking
1974· Person
ProvenTested many times; part of working physics.
British theoretical physicist (1942–2018), Cambridge professor, who showed black holes glow and evaporate.
See it on the Science map →How it works
Diagnosed with motor neurone disease (ALS) at 21, Hawking worked for decades through a wheelchair and speech computer. He extended Penrose's singularity theorems to the whole universe, proved that a black hole's horizon area never shrinks (1971), and in 1974 found that quantum effects make black holes emit heat. He thought in pictures and geometry. His 1988 book "A Brief History of Time" sold millions of copies.
Why it matters
He first joined gravity, quantum theory and thermodynamics in one result, and posed the information paradox that still drives quantum-gravity research.
How the work held up
His singularity work is mathematical proof. LIGO data (2021, 2025) confirmed his area theorem. Hawking radiation itself is too faint to detect; lab analogs (2016, 2019) behave as he predicted.
Still a mystery
He argued information is destroyed in black holes, then conceded in 2004. His "no-boundary" origin of the universe remains untested.
Connections (7)
▸Stephen Hawking with Penrose, proved theorems on Singularities: where physics breaksProven
The relationship
Hawking realized Penrose's argument could be run backward in time. An expanding universe is like a collapsing star played in reverse, so the same reasoning implies our universe began from a singularity. Together in 1970 they proved a general theorem covering both black holes and cosmology, under assumptions about gravity and ordinary matter.
How the link was found
Hawking's 1966 PhD thesis and papers from 1965–67, then the joint Hawking–Penrose theorem published in 1970.
Why it's proven
These are accepted mathematical proofs within general relativity. Their conditions are believed to hold for ordinary matter; quantum effects and inflation can bend them.
Open questions and mysteries
Hawking later argued, with the no-boundary proposal, that quantum effects remove the initial singularity. That is unconfirmed.
▸Stephen Hawking discovered Hawking radiation: black holes evaporateWell supported
The relationship
Hawking set out to disprove Bekenstein's claim that black holes have entropy, since that implied a temperature, and anything with a temperature must glow. Applying quantum field theory near a horizon, he found black holes do glow, with a temperature inversely proportional to their mass. He then realized they must slowly lose mass and eventually evaporate.
How the link was found
Stephen Hawking, "Black hole explosions?" in Nature, March 1974, with the full derivation in 1975.
Is it proven?
The calculation is widely rederived and accepted. Lab analogs, such as Jeff Steinhauer's sound-wave horizons in ultracold atoms (2016, 2019), show matching behavior. Direct observation is impossible with current tools.
Open questions and mysteries
Whether tiny primordial black holes from the early universe exist and are evaporating today, which would make the radiation visible.
▸Stephen Hawking pinned down the exact value of Black-hole entropy: information on the surfaceWell supported
The relationship
Bekenstein argued a black hole's entropy is proportional to its horizon area, but could not fix the exact number. Hawking's 1974 temperature result settled it. In thermodynamics, temperature and entropy are tied together, so knowing the temperature pins down the entropy exactly: one quarter of the horizon area, measured in Planck units. This is the Bekenstein–Hawking formula.
How the link was found
Stephen Hawking, 1974–75, as a direct consequence of his radiation calculation.
Is it proven?
The quarter factor has been rederived by several methods, and string theory reproduced it exactly for special black holes in 1996.
Open questions and mysteries
What microscopic states the entropy counts for ordinary, spinning black holes is unknown.
▸Stephen Hawking posed The black-hole information paradoxOpen question
The relationship
Hawking showed his radiation is exactly thermal, carrying no record of what fell in. Once a black hole evaporates completely, the information seems gone, breaking the quantum rule that it is always preserved. He argued quantum mechanics must change. Many physicists disagreed, and the dispute became the black-hole information paradox, a decades-long contest of ideas.
How the link was found
Hawking, 1976. In 1997 Hawking and Kip Thorne bet John Preskill that information is lost. Hawking conceded in 2004, giving Preskill a baseball encyclopedia.
Is it proven?
The paradox is a genuine contradiction between two well-tested theories. Its resolution is not proven; theoretical work since 1997 points strongly toward information surviving.
Open questions and mysteries
Hawking's 2004 concession and later "soft hair" work (2016) did not settle exactly how the information escapes.
▸Stephen Hawking asked what "breathes fire into the equations" in Did the laws of physics come first?Philosophy
The relationship
Hawking saw that even a final theory would be just equations. In 1988 he asked what breathes fire into them and makes a universe for them to describe. In 2010 he and Mlodinow answered boldly: because a law like gravity exists, the universe can create itself from nothing. Critics replied that this simply assumes the law.
How the link was found
'A Brief History of Time' (1988), final chapter; 'The Grand Design' with Leonard Mlodinow (2010). Thomas Hertog's 2023 book 'On the Origin of Time' says Hawking finally held that laws emerge with the universe.
Is it proven?
No experiment addresses it; it is philosophy. Hertog presents their last joint papers (2018) as steps toward a theory in which laws are not fixed in advance. That remains untested.
Open questions and mysteries
If laws emerged with the universe, what governed their emergence? Hawking's 1988 question still lacks a settled answer.
▸Stephen Hawking proposed with James Hartle The no-boundary proposal (Hartle–Hawking)Speculative
The relationship
Hawking brought the cosmology; Hartle, at UC Santa Barbara, brought quantum methods for whole systems. Together they wrote down a specific 'wave function of the universe', the first concrete rule for its quantum starting state. Hawking then popularized it, writing in 1988 that a universe with no boundary would simply be, and asking what place that left for a creator.
How the link was found
Hawking first floated it at a 1981 Vatican conference on cosmology, where, he recalled, Pope John Paul II urged scientists not to probe the beginning itself. Hartle and Hawking published 'Wave function of the Universe' in 1983.
Is it proven?
Untested. From the 2000s Hawking developed it with Thomas Hertog into a 'top-down' view, in which the present universe selects its likely histories. James Hartle (1939–2023) continued the work too.
Open questions and mysteries
Did Hawking's final, observer-centered version improve the proposal or abandon its original simplicity? Colleagues still disagree.
▸Stephen Hawking pioneered the idea behind Primordial black holes as dark matterSpeculative
The relationship
Hawking argued in 1971 that lumps in the early universe could collapse into black holes as light as a hundred-thousandth of a gram. Asking what such tiny black holes do led him in 1974 to find that black holes radiate, and smaller ones are hotter. So primordial black holes lighter than about a kilometer-wide asteroid would have exploded by now, setting a lower limit for dark matter.
How the link was found
Yakov Zel'dovich and Igor Novikov first considered early-universe black holes in 1966. Hawking's 1971 paper developed the idea; Bernard Carr and Hawking (1974) showed they would not swallow everything. In 1976 Don Page and Hawking used gamma rays to cap their numbers.
Is it proven?
Hawking radiation is accepted theory but unobserved. Gamma-ray telescopes (Fermi, HAWC) have seen no exploding black holes, which limits how many small primordial ones exist.
Open questions and mysteries
Could a primordial black hole explode nearby, giving the first direct test of Hawking radiation? A few theorists have even suggested one could be the hypothetical 'Planet Nine' beyond Neptune.