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Stephen Hawking's final paper revealed, showing professor's last statement on the universe before his death

Universe is finite and more simple than we'd thought, paper suggests

Andrew Griffin
Wednesday 02 May 2018 15:27 BST
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Stephen Hawking in quotes

Stephen Hawking's final statement on the universe has been revealed: it is more finite and more simple than we might have thought.

The famous physicists final work, submitted before his death, has been published in the Journal of High Energy Physics. Written with Belgian physicists Thomas Hertog, it delves into how the universe began.

The two worked on the groundbreaking paper towards the very end of Mr Hawking's life, even as that work and communicating about it became very difficult. It uses new thinking – based on the idea that our universe is a very large and complex hologram – to suggest that a popular account of the beginning of our universe is wrong.

The usual theory of the Big Bang says that our universe was created just a moment after it happened, as the universe started expanding more and more quickly. Many belief that in some parts of reality the expansion never stops, meaning that the universe that surrounds us is just a strange place where that expansion has stopped and space has become inhabitable.

That theory suggests there are other places in that vast multiverse that might have wildly different laws of physics to our own, and where that inflation is still happening. Our universe is just one of a range of small pockets sprinkled throughout space – which, by chance, has the conditions required for our complex life and everything needed for it to form.

“The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean,” said Professor Hawking in an interview last autumn.

“The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse. But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite the theory can’t be tested."

But Professor Hawking's last work suggests that idea of eternal inflation is wrong. It will eventually come to an end, he writes with his collaborator.

“The problem with the usual account of eternal inflation is that it assumes an existing background universe that evolves according to Einstein’s theory of general relativity and treats the quantum effects as small fluctuations around this,” said Professor Hertog. “However, the dynamics of eternal inflation wipes out the separation between classical and quantum physics. As a consequence, Einstein’s theory breaks down in eternal inflation.”

In fact, the universe is a rather more simple and smooth than previously thought, the study suggests.

“We predict that our universe, on the largest scales, is reasonably smooth and globally finite. So it is not a fractal structure,” said Professor Hawking.

Now Professor Hawking's successors will be able to put the predictions to the test in the real world. If they are confirmed, they could dramatically change our understanding of how the universe is constructed.

“We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes,” said Professor Hawking.

Some of the more concrete predictions of the theory can be studied by looking through data from our advanced space telescopes. Professor Hertog has suggested that by listening for primordial gravitational waves we might be able to hear proof of his and Mr Hawking's last finding: if the universe has really been expanding, those ripples in spacetime should be too big for us to hear, but if the final paper is correct then we should hear the proof as those disturbances go past.

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