Stephen Hawking was a theoretical physicist and cosmologist best known for advancing theoretical models on black holes and cosmic inflation, which he discusses in his popular writing on time and space.

Hawking's university education began in 1959, when, at age 17, he attended University College, Oxford, to study physics. Seeking a PhD at University of Cambridge, Hawking was disappointed to learn that the esteemed astronomer Fred Hoyle – who is now famous for coining the term 'Big Bang' theory by mocking it on radio – wouldn't be taking any more students.

His supervisor was a relatively unknown researcher by the name of Dennis Sciama. What Sciama lacked in fame he more than made up for in mentorship, encouraging a young Hawking to follow his interests. Where Hoyle was dismissive of the Big Bang, Hawking became its champion.

## What was Stephen Hawking's discovery on the Big Bang?

Following Roger Penrose's work on the infinitely dense point of spacetime at the centres of black holes, Hawking used the mathematics of general relativity to argue the origins of the Universe itself could be found in similar physics.

In 1970, Hawking and Penrose published their now famous theory on cosmological singularities, which describes the starting energy of the Universe all contained in an infinitely small volume.

## What were Stephen Hawking's discoveries on black holes?

A key concern with the concept of black holes at that time was that according to the second law of thermodynamics, the overall amount of disorder (or entropy) in a closed system like the Universe increases with time.

Since black holes can't reflect or emit light or matter, this disorder could in effect disappear. Either the long-established law on entropy was wrong, or somehow, a measure of this disorder sticks around.

A theoretical physicist named Jacob Bekenstein had an answer. A graduate student at the time, Bekenstein reasoned that if the area of a black hole's 'event horizon' surface expands as light and matter falls in, it could provide a measure of its entropy.

If true, this increased disorder would result in an amount of heat in relation to the black hole's surface. Hawking, aiming to disprove Bekenstein's hypothesis, instead uncovered a mathematical relationship between thermal radiation and the expanding event horizon.

Referred to as 'Hawking radiation', the discovery was initially controversial, as it implied even large black holes could evaporate away over a long period of time, creating yet another paradox over the conservation of information in the Universe.

While it has yet to be observed, Hawking radiation is now a largely accepted feature of these exotic cosmic objects.

## Why is Stephen Hawking so popular today?

In 1979, Hawking was elected Lucasian Professor of Mathematics at the University of Cambridge, a position once held by the mathematician Isaac Newton. Over the ensuing years Hawking earned fame for his ideas, not just in the scientific community but in households around the world.

Published in 1988, his popular science book on the strange nature of time and space, A Brief History of Time, broke records by remaining on the *Times of London* bestseller list for 237 weeks. That's more than four and a half years.

## Bio

**Born**: 8 January 1942 to tropical medicine researcher Frank Hawking and economics and philosophy student, Isobel Eileen Hawking.

**Died**: 14 March 2018, age 76.

**As a person**: Hawking was diagnosed with 'amyotrophic lateral sclerosis' (ALS), a type of motor neurone disease, at the age of 21. Though initially given just two years to live, the degenerative condition progressed slower than expected, and he continued working for decades with the support of his family and friends.

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