From the Big Bang to black holes: Stephen Hawking's 'rare genius' helped shine a light on some of the universe's biggest mysteries

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Stephen Hawking probed the very limits of human understanding both in the vastness of space and in the bizarre sub-molecular world of quantum theory.

As well as numerous best-selling books, Hawking also published several important scientific papers during an illustrious research career.

Through his groundbreaking theories, the legendary physicist and 'rare genius' examined the origins of the universe and helped explain the behaviour of black holes.

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Stephen Hawking, who sought to explain some of the most complicated questions of life while working under the shadow of a likely premature death, has died at 76

1970: Space-time in black holes 

One of Hawking's first key ideas was how space and time react within the brutal confines of black holes.

Black holes are regions of space with a gravitational field so intense that no matter or radiation can escape.

The objects are so powerful they bend time and space in bizarre ways, and in 1970 Hawking showed how black holes alter 'space-time'.

'Space-time' is a theory used by physicists to describe the fusion of 3D space and time into a four-dimensional continuum.

Up until the '70s physicists had known Einstein's theory allowed for 'singularities' - points where space-time appeared to be infinitely curved.

But it was unclear whether or not these singularities actually existed.

Birkbeck College physicist Sir Roger Penrose showed that singularities do exist as they can form in black holes.

Alongside Sir Penrose, Hawking applied the same idea to the universe in its entirety in 1970.

They showed that Einstein's theory predicted a singularity in our distant past: The Big Bang.

1971-72: Black hole mechanics

Black holes are regions of space with a gravitational field so intense that no matter or radiation can escape.

Their field is so intense that they form their own set of physical laws unlike anything else in the universe.

Hawking devised the second law of black holes, which states that the total surface area of a black hole will never get smaller. 

In separate work, Hawking sparked the 'no hair' theorem of black holes.

This states that black holes can be characterised by three numbers – their mass, charge and angular momentum.

The 'hair' in Hawking's idea is other information that disappears when it falls into the black hole.

1974-75: Vanishing black holes

Hawking showed that black holes emit heat and eventually vanish in an extremely slow process.

While a black hole with the mass of the sun would take longer than the age of our universe to evaporate, smaller ones disappear faster.

Near the end of their lives they release heat at a dramatic rate, with an average-sized black hole releasing the energy of a million hydrogen bombs in just a tenth of a second.

Hawking's drew on 'quantum theory' for the finding - the branch of physics concerned with how the universe works at the subatomic level.

Through his groundbreaking theories, the legendary physicist helped explain the behaviour of black holes (artist's impression) and examined the origins of the universe

WHAT DOES PROFESSOR STEPHEN HAWKING THINK HAPPENED BEFORE THE BIG BANG?

Professor Stephen Hawking believes that before the Big Bang 3.7 billion years ago, time and space as we know it did not exist.

According to his theory, the universe was shrunk and condensed to an incredibly dense ball of heat and energy the size of a single atom.

Inside this speck, the laws of physics and time as we know them cease to function, and time as we understand it did not exist.

If we move back in time from the Big Bang, the 'arrow' of time shrinks infinitely as the universe becomes smaller, never reaching a clear starting point.

Professor Stephen Hawking believes that before the Big Bang 3.7 billion years ago, time and space as we know it did not exist

Hawking said in an interview in March 2018 that before the Big Bang, time was bent - 'It was always reaching closer to nothing but didn't become nothing.'

Essentially, 'there was never a Big Bang that produced something from nothing. It just seemed that way from mankind's point of perspective.'

In a lecture on the so-called no-boundary proposal, Hawking wrote: 'Events before the Big Bang are simply not defined, because there's no way one could measure what happened at them.

Since events before the Big Bang have no observational consequences, one may as well cut them out of the theory, and say that time began at the Big Bang.'

1982: How galaxies arise

Many physicists believe the universe inflated rapidly shortly after the Big Bang.

Hawking was one of the first to show how galaxies may have formed during this explosion of time and space.

He found that quantum fluctuations - tiny variations in the distribution of matter - grew into the galaxies that dot the cosmos today.

This is because strong gravitational forces made matter clump together.

Hawking's theory is supported by recent observations of the faint afterglow of the Big Bang, which spotted the sort of variations Hawking worked with.

Speaking on Hawking's passing, renowned British cosmologist Professor Lord Martin Rees said: 'Specially influential were his contributions to 'cosmic inflation' – a theory that many believe describes the ultra-early phases of our expanding universe.

'A key issue is to understand the primordial seeds which eventually develop into galaxies.

'He proposed that these were quantum fluctuations – somewhat analogous to those involved in 'Hawking radiation' from black holes.

'He hosted an important meeting in 1982 where such ideas were thoroughly discussed.

'Subsequently, particularly with James Hartle and Thomas Hertog, he made further steps towards linking the two great theories of 20th century physics: the quantum theory of the microworld and Einstein's theory of gravity and space-time.'

WHAT DID STEPHEN HAWKING BELIEVE ABOUT DEATH?

Professor Stephen Hawking had one of the most remarkable brains of the past century. 

The British physicist applied his mind to confront the questions that surrounded the Big Bang, black holes and string theory. 

As well as the most complex and challenging questions in quantum mechanics, Hawking also confronted the challenge of death. 

After being diagnosed with motor neuron disease at the age of 21, he lived with the debilitating illness for 55 years. 

With an initial diagnosis of two years left to live, Hawking defied all odds.

He lived with the prospect of an early death for decades - and it made him confront its dark realities head on.

In a 2011 interview with The Guardian, Professor Hawking said: 'I'm not afraid of death, but I'm in no hurry to die. I have so much I want to do first.'

With such a philosophical approach to life and possessing one of the most analytical minds the world has ever seen, Professor Hawking was inspirational in his strength.

One of the most brilliant minds of all-time, and the leading scholar on the topic of black holes, Professor Stephen Hawking (pictured) believed that life after death was a myth

For many, the comfort of an after life is something which offers reassurance approaching death.

Hawking, however, saw death very differently. 

Although the man inspired millions through his books, lectures, theories and the recent biopic about his life, Professor Hawking did not believe in life after death.  

In the same 2011 interview, he said: 'I regard the brain as a computer which will stop working when its components fail.

'There is no heaven or afterlife for broken down computers; that is a fairy story for people afraid of the dark.'

In the case of Professor Hawking, he believed that living your best life was more important than hoping for a heaven.  

 'We should seek the greatest value of our action,' he said, when asked how we should live.

Arguably the person who understood the foundation of the universe better than anyone, it offered a unique perspective to him.

'Science predicts that many different kinds of universe will be spontaneously created out of nothing. It is a matter of chance which we are in,' he said. 

Hawking was a long-time critic of the idea of a deity and religions. 

He believed that it was natural for people to believe in an all-powerful God before science offered an explanation. 

In his opinion, science now offered a clearer and more thorough explanation than faith. 

1983: How the universe began

Hawking is best known for his attempts to combine two key theories of physics: Quantum theory and Einstein's general relativity.

While quantum theory covers how tiny subatomic particles stitch together the fabric of our universe, general relativity deals with larger objects.

It describes how galaxies, stars, black holes, planets and more interact with one another via gravitational forces. 

Much of Hawking;s work focussed on combining quantum theory and general relativity with Einstein's theory of gravity. 

He suggested that this new theory, known as quantum gravity, could fill in many of the gaps of our current understanding of physics and the universe.

In 1983 the physicist partnered with Chicago University's Professor Jim Hartle to propose a 'wave function of the universe'.

Known as the Hartle-Hawking state, this notion is meant to figure out how the universe began through quantum mechanics.

In theory, this could be used to understand the properties of the universe around us.

1988: A brief history of time

Hawking's bestselling book A Brief History of Time has sold more than ten million copies since it was first published in 1988

Hawking's bestselling book A Brief History of Time has sold more than ten million copies since it was first published in 1988.

The book, which described the structure, origin, development and eventual fate of the universe, was a surprise success for the relatively unknown physicist, staying in the Sunday Times bestseller list for 237 weeks. 

Hawking wrote the book for readers with no knowledge of any scientific theories.

The physicist joked himself that many who owned the book struggled to understand its complexity and never finished it.

The book ultimately propelled Hawking to stardom, with the physicist publishing or co-publishing 15 books in total and writing or starring in multiple scientific documentaries, television shows, films and more.

What happened before the Big Bang?

At the time of the Big Bang 13.8 billion years ago, all matter in the universe erupted from a singularity to create the cosmos.

But scientists are unsure what happened before then.

In a TV interview that aired earlier this month, Hawking said 'nothing was around before the Big Bang'.

Instead, time and space existed in a 'bent state' that was distorted along another dimension.

The physicist believes the Big Bang was the formation of what we now regard as time because the event broke down the laws of physics.

This means that anything that preceded it cannot be applied to our understanding of time and existence. 

Of his discoveries, Canadian astronaut Chris Hadfield said: 'Genius is so fine and rare. Goodbye Professor Hawking. You inspired us all.'