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Sunday 19 August 2018

A brief history of Stephen Hawking's greatest discoveries: 'Fact is stranger than fiction'

Professor Stephen Hawking death
Professor Stephen Hawking death

Sarah Knapton

Stephen Hawking, who died on Wednesday aged 76, once remarked that ‘fact is stranger than fiction and nowhere is this more true than in the case of black holes.’

And it was for his work unpicking the ruinous anomalies of spacetime that Hawking will be most remembered.

The theory behind black holes had already been proposed by Cambridge don John Mitchell in 1783 in the Philosophical Transactions of the Royal Society.

He called them dark stars. Burnt out furnaces which had collapsed into objects so massive and compact they generated a gravitational field capable of dragging back light itself, and leading to what appeared to be an empty void in space.

FILE - In this Monday, Nov. 28, 2016 file photo Pope Francis greets physicist Stephen Hawking during an audience with participants at a plenary session of the Pontifical Academy of Sciences, at the Vatican. (L'Osservatore Romano/pool photo via AP, File)
FILE - In this Monday, Nov. 28, 2016 file photo Pope Francis greets physicist Stephen Hawking during an audience with participants at a plenary session of the Pontifical Academy of Sciences, at the Vatican. (L'Osservatore Romano/pool photo via AP, File)
File photo dated 9/12/2014 of Professor Stephen Hawking (front), who has died aged 76, with (from left) Felicity Jones, Jane Hawking and Eddie Redmayne, attending the UK Premiere of The Theory of Everything at the Odeon Leicester Square, London. Ian West/PA Wire
File photo dated 25/02/12 of Professor Stephen Hawking, who has died aged 76, posing beside a lamp titled 'black hole light' by inventor Mark Champkins, presented to him during his visit to the Science Museum in London. Anthony Devlin/PA Wire
File photo dated 09/09/1992 Professor Stephen Hawking, who had died aged 76, and Nobel Prize winner Dorothy Hodgkin, with their portraits unveiled at the National Portrait Gallery in London. /PA Wire
File photo dated 08/02/2015 of Eddie Redmayne and Professor Stephen Hawking, who has died aged 76, arriving at the After-party dinner for the EE British Academy Film Awards at Grosvenor House Hotel in London. Daniel Leal-Olivas/PA Wire
File photo dated 19/09/08 of Professor Stephen Hawking, who has died aged 76, during the unveiling of The Corpus Clock, a new installation at Corpus Christi College at Cambridge University. Chris Radburn/PA Wire
File photo dated 29/04/10 of Professor Stephen Hawking, who has died aged 76, watching the first preview of his new show for the Discovery Channel, Stephen Hawking's Universe. David Parry/PA Wire
U.S. President Barack Obama presents the Medal of Freedom to scientist Stephen Hawking during a ceremony in the East Room of the White House in Washington, August 12, 2009. REUTERS/Jason Reed/File photo
CEO of ZERO-G Peter Diamandis (L) and British physicist Stephen Hawking stand on lift truck after his flight at Kennedy Space Center in Cape Canaveral, Florida April 26, 2007. REUTERS/Charles W Luzier/File photo
Theoretical physicist Stephen Hawking and his daughter Lucy arrive at the British Academy of Film and Arts (BAFTA) awards ceremony at the Royal Opera House in London February 8, 2015. REUTERS/Suzanne Plunkett/File photo
Former South African President Nelson Mandela (R) meets theoretical physicist professor Stephen Hawking at Mandela's Foundation office in Johannesburg May 15, 2008. Pool/via REUTERS/File photo
Microsoft President Bill Gates (L), accompanied by University Vice-Chancellor Professor Alec Broers, meets Professor Stephen Hawking on a visit to Cambridge University October 7, 1997. REUTERS/Stringer/File photo
Jane Wilde Hawking kisses her ex-husband Stephen Hawking as she arrives at the UK premiere of the film "The Theory of Everything" which is based around Stephen Hawking's life, at a cinema in central London December 9, 2014. REUTERS/Andrew Winning/File
British physicist Stephen Hawking delivers a lecture on "The Origin of the Universe" at the Heysel conference hall in Brussels May 20, 2007. REUTERS/Francois Lenoir/File photo
Britain's Queen Elizabeth (L) meets Stephen Hawking during a reception for Leonard Cheshire Disability charity at St James's Palace in London May 29, 2014. Jonathan Brady/Pool via REUTERS/File photo

Yet the theory fell down after it was discovered that light always travels at a speed of one hundred and eighty six thousands miles per second, no matter where it has come from or where it is going.

He called them dark stars. Burnt out furnaces which had collapsed into objects so massive and compact they generated a gravitational field capable of dragging back light itself, and leading to what appeared to be an empty void in space.

Yet the theory fell down after it was discovered that light always travels at a speed of one hundred and eighty six thousands miles per second, no matter where it has come from or where it is going.

How then could the gravity of a collapsed star slow it down enough to pull it back?

The answer was not solved until in 1915 Albert Einstein put forward his revolutionary General Theory of Relativity which showed space and time are not constant, but can be bent by gravity.

Four years later a British expedition in West Africa which was monitoring a solar eclipse noticed that the stars had shifted slightly from their usual positions. It proved that their light had been bent by curved spacetime near the Sun and confirmed Einstein’s theory of General Relativity.

hawking 2.JPG

In his book A Brief History of Time, Hawking famously described spacetime as a rubber sheet which could be bent by a heavy ball - representing a huge body such as star or planet - in the centre. As the ball became heavier and heavier eventually a bottomless hole would form, from which nothing could escape. A black hole would form.

“In space, no one can hear you scream; and in a black hole, no one can see you disappear,” Hawking once quipped.

Hawking’s own contribution to the field began after reading a paper by Roger Penrose when he was studying at Cambridge in 1965.

The following year, in his PhD thesis Properties of the Expanding Universe, Hawking  showed that the universe could have come out of a singularity without evolving perfectly smoothly.

Working with Penrose, Hawking demonstrated that black holes could exist mathematically, culminating in the singularity theorem in 1970.

Writing in A Brief History of Time, Hawking wrote: “The work that Roger Penrose and I did between 1965 and 1970 showed that, according to general relativity, there must be a singularity of infinite density and spacetime curvature within a black hole.

"This is rather like the Big Bang at the beginning of time. At this singularity the laws of science and our ability to predict the future would break down.”

Hawking then turned his attention to the thermodynamics of black holes in an attempt to understand how they could be a steady temperature if they absorbed all heat falling into them, but could not emit anything in return.

Hawking radiation

After turning to quantum mechanics, he realised to his surprise that black holes were not black at all. Instead they ‘emitted particles at a steady rate’ from the event horizon, an ejection which came to be known as ‘Hawking radiation’.

The radiation occurs because quantum fluctuations near the event horizon create pairs of particles, the negative one of which gets sucked into the black hole, while the positive one escapes.General relativity suggested that black holes could only get bigger and bigger. But by bringing quantum theory into the mix, Hawking showed they could “evaporate” and explode as the flow of negative energy particles reduces the mass of the black hole.

It demonstrated that although black holes were set apart from the space-time continuum, they could have important effects on it.

hawking.JPG

“If information were lost in black holes, we wouldn't be able to predict the future, because a black hole could emit any collection of particles,” Hawking said.

“It could emit a working television set, or a leather bound volume of the complete works of Shakespeare, though the chance of such exotic emissions is very low.”

Although it became widely accepted, Hawking Radiation was never proved by astronomers or physicists - if it had, it would almost certainly have earned him the Nobel Prize.

Quantum gravity

Hawking’s paper also served another purpose. For the first time it combined theories of quantum physics with general relativity, theories believed to be incompatible, because scientists had largely found that the same rules of physics did not apply to things that were very big or very small.

It spurred Hawking towards finding a ‘grand unified theory’ which would describe the behaviour of all matter in the universe. In 1988, he explored this issue in A Brief History of Time, which sold more than 25 million copies.

"It would be the ultimate triumph of human reason - for the we would know the mind of God," he concluded in the book.

In work which would continue up to his death., Hawking attempted to solve the problem quantum gravity - imposing the properties of tiny particles on to the structure of spacetime.

He theorised the ‘no boundary’ idea of singularities, where the single point in space time is replaced by a kind of cap, similar to the North Pole, where the concept of longitude loses meaning, also the pole itself is still mappable.

Theoretical physicists continue to work towards at grand unified theory.

Telegraph.co.uk

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