IN CONTEXT
Cosmology
1783 John Michell theorizes objects whose gravity is so great that they trap light.
1930 Subrahmanyan Chandrasekhar proposes that a collapsing stellar core above a certain mass would give rise to a black hole.
1971 The first likely black hole is identified – Cygnus X-1.
2002 Observations of stars orbiting close to the centre of our galaxy suggest the presence of a giant black hole.
2012 American string theorist Joseph Polchinski suggests that quantum entanglement produces a super-hot “firewall” at a black hole’s event horizon.
2014 Hawking announces that he no longer thinks black holes can exist.
In the 1960s, British physicist Stephen Hawking was one among several brilliant researchers who became interested in the behaviour of black holes. He wrote his doctoral thesis on the cosmological aspects of a singularity (the point in space-time at which all of a black hole’s mass is concentrated), and drew parallels between the singularities of stellar-mass black holes and the initial state of the Universe during the Big Bang.
Around 1973, Hawking became interested in quantum mechanics and the behaviour of gravity on a subatomic scale. He made an important discovery – that despite their name, black holes do not just swallow up matter and energy but emit radiation. So-called “Hawking radiation” is emitted at the black hole’s event horizon – the outer boundary at which the black hole’s gravity becomes so strong that not even light can escape. Hawking showed that in the case of a rotating black hole, the intense gravity would give rise to the production of virtual, subatomic particle-antiparticle pairs. On the event horizon, it would be possible for one element of each pair to be pulled into the black hole, effectively boosting the survivor into a sustained existence as a real particle. The result of this to a distant observer is that the event horizon emits low-temperature thermal radiation. Over time, the energy carried away by this radiation causes the black hole to lose mass and evaporate away.
"My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all."
Stephen Hawking
See also: John Michell • Albert Einstein • Subrahmanyan Chandrasekhar