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Stephen Hawking's big ideas challenged our understanding of the world

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Renowned physicist Professor Stephen Hawking died at age 76 on Wednesday, but his ideas will likely live on for generations to come.

Professor Stephen Hawking's formidable mind probed the very limits of human understanding both in the vastness of space and in the bizarre sub-molecular world of quantum theory. Here's just a few of his big ideas.

Black holes

Professor Hawking extensively researched black holes - the regions of space-time where gravity is so strong that nothing, not even light, can escape.

His early research was pivotal in understanding how the big bang could have been the start of the universe.

A star being swallowed by a black hole.
A star being swallowed by a black hole.
NASA

Working with mathematician Roger Penrose, Hawking found that black holes acted like the big bang in reverse.

According to the BBC, this was a "key moment in showing the big bang really happened".

'Real time' and 'imaginary time'

Hawking worked on marrying the two cornerstones of modern physics - Einstein's General Theory of Relativity, which concerns gravity and large-scale phenomena, and quantum theory, which covers subatomic particles.

As a result of that research, Hawking proposed a model of the universe based on two concepts of time: "real time", or time as human beings experience it, and quantum theory's "imaginary time", on which the world may really run.

Real time could be perceived as a horizontal line, he said.

"On the left, one has the past, and on the right, the future. But there's another kind of time in the vertical direction. This is called imaginary time, because it is not the kind of time we normally experience - but in a sense, it is just as real as what we call real time," Hawking said. 

Time travel

Hawking's studies left him convinced that time travel could exist.

So much so that he threw a party for time travellers in 2009. The party was complete with champagne and appetisers, but he didn't release the invitations until after the party had taken place.

Professor Stephen Hawking was all alone at his party for time travellers.
Professor Stephen Hawking all alone at his party for time travellers.
Twitter

If people showed, he contended, it would be proof that time travel existed.

Unfortunately, no one came.

In an interview with Ars Technica, Hawking said: 'We are all travelling forward in time anyway. We can fast forward by going off in a rocket at high speed and return to find everyone on Earth much older or dead.

"Einstein's general theory of relativity seems to offer the possibility that we could warp space-time so much that we could travel back in time. 

"However, it is likely that warping would trigger a bolt of radiation that would destroy the spaceship and maybe the space-time itself."

Artificial life

 Professor Stephen Hawking, who has died aged 76, watching the first preview of his new show for the Discovery Channel, Stephen Hawking's Universe
Professor Stephen Hawking, who has died aged 76, watching the first preview of his new show for the Discovery Channel, Stephen Hawking's Universe.
AAP

Hawking caused some controversy among biologists when he said he saw computer viruses as a life form, and thus the human race's first act of creation.

"I think it says something about human nature that the only form of life we have created so far is purely destructive,” he told a computer forum in Boston. "We've created life in our own image."

He also predicted the development of a "race of self-designing human beings, who will use genetic engineering to improve their make-up".

God

In his book A Brief History of Time, Hawking wrote that the discovery of a unifying set of scientific principles known as the theory of everything would enable scientists to "know the mind of God." 

But in his later years, Hawking clarified that he was an atheist, telling Spanish newspaper El Mundo: "Before we understand science, it is natural to believe that God created the universe. But now science offers a more convincing explanation. What I meant by 'we would know the mind of God' is, we would know everything that God would know, if there were a God, which there isn't. I'm an atheist."

At another public lecture, he mused: "What was God doing before the divine creation? Was he preparing hell for people who asked such questions?"

Additional reporting: Nick Baker

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