Stephen Hawking was a theoretical physicist, cosmologist and author. He was the director of research at the Centre for Theoretical Cosmology at the University of Cambridge before he died two years ago.
His incredible scientific work included working with Roger Penrose on the gravitational singularity theorems as part of general relativity and the theoretical prediction that black holes emit radiation, often referred to as Hawking radiation.
He was the first to propose a theory of cosmology explained by the union of general theory of relativity and quantum mechanics. But Hawking was also intrigued by how the end of the world would happen and even wrote a “near-certain” doomsday date.
He outlined how this could unfold during his ‘Into the Universe’ series.
He said: “What caused the expansion, or inflation of the universe in the first place?
“When we can answer that, and fully understand the Big Bang, we will also learn the fate of the universe.
“The key to it all is something called dark energy – a mysterious form of energy that pushes space itself apart, even if gravity is pushing space together.
“It seems as if dark energy provided the kick which inflated the universe, although we are not quite sure how.
“What is certain is the fate of the universe depends on how this dark energy behaves.”
Dark energy is causing the rate of expansion of our universe rather than slowing down over time, challenging theories of a universe that began in a Big Bang.
Prof Hawking explained: “If it slowly weakens, then gravity could get the upper hand and, in 20 billion years or so, the universe would go into reverse and drive everything back to where it came.
“Space itself would contract. This is known as the Big Crunch.
“I think it’s more likely that dark energy will drive the expansion of the universe forever.
“Ultimately, everything will just keep spreading out, until the universe is cold and dark.
“Everything will become so far apart that even gravity will be defeated.”
He put forward an alternative theory.
He added: “I think a Big Chill is what we have in store. Not a Big Crunch.
“So will this be the end of us and life as we know it? Or will we figure out how to navigate to a new universe before then?
“I think we will only know once we truly understand why the universe exists at all.
“Perhaps then, when we finally unravel the whole cosmic puzzle, we will become masters – not just of our own universe, but the universe next door.”