Home   Business   Article

Stephen Hawking's final work suggests the universe is simpler than we thought


By Paul Brackley


Professor Stephen Hawking in March 2015. Picture: Andre Pattenden
Professor Stephen Hawking in March 2015. Picture: Andre Pattenden

Cambridge thereotical physicist and Prof Thomas Hertog reduce the multiverse and say there is boundary in our past

Stephen Hawking at his 75th Birthday public symposium. Pictures: Sir Cam
Stephen Hawking at his 75th Birthday public symposium. Pictures: Sir Cam

Professor Stephen Hawking’s final work has been published – and it suggests that the universe is finite and far simpler than many current models suggest.

The Cambridge theoretical physicist worked in collaboration with Prof Thomas Hertog from KU Leuven on the theory.

Submitted before Prof Hawking’s death on March 14 and now published in the Journal of High Energy Physics, it uses string theory to explain the nature of our universe.

Modern theories suggest our local universe came into existence with a brief burst of inflation – meaning that a tiny fraction of a second after the Big Bang, the universe expanded at an exponential rate. It is widely believed that there are regions where this inflation never stops due to quantum effects. This means that globally, inflation is eternal and the observable part of our universe is like a bubble or pocket – a region in which inflation has ended and stars and galaxies formed.

This long-exposure Hubble Space Telescope image of massive galaxy cluster Abell 2744 (foreground) is the deepest ever made of any cluster of galaxies. It shows some of the faintest and youngest galaxies ever detected in space. Image: NASA/ESA
This long-exposure Hubble Space Telescope image of massive galaxy cluster Abell 2744 (foreground) is the deepest ever made of any cluster of galaxies. It shows some of the faintest and youngest galaxies ever detected in space. Image: NASA/ESA

In an interview last autumn, Prof Hawking said: “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. 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.”

Prof Hertog announced the new theory at a conference in Cambridge last year to mark Prof Hawking’s 75th birthday.

It says the account of eternal inflation as a theory of the Big Bang is wrong.

“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 Prof 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.”

Professor Stephen Hawking in March 2015. Picture: Andre Pattenden
Professor Stephen Hawking in March 2015. Picture: Andre Pattenden

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

Their alternative is based on string theory – a branch of theoretical physics that attempts to reconcile gravity and general relativity with quantum physics, partly by describing the fundamental constituents of the universe as tiny vibrating strings.

They employ the string theory concept of holography, which suggests that the universe is a large, complex hologram – meaning physical reality in certain 3D spaces can be mathematically reduced to 2D projections on a surface.

Prof Hawking and Prof Hertog’s variation of this concept of holography projects out the time dimension in eternal inflation. This enables them to describe eternal inflation without relying on Einstein’s theory. They reduce eternal inflation to a timeless state defined on a spatial surface at the beginning of time.

Prof Stephen Hawking, with sister Dr Mary Hawking, at the Moller Centre commending theirfathers role in progress towards NTD elimination. Picture: Keith Heppell
Prof Stephen Hawking, with sister Dr Mary Hawking, at the Moller Centre commending theirfathers role in progress towards NTD elimination. Picture: Keith Heppell

Prof Hertog said: “When we trace the evolution of our universe backwards in time, at some point we arrive at the threshold of eternal inflation, where our familiar notion of time ceases to have any meaning.”

In 1983 Prof Hawking’s famous ‘no boundary theory’ with physicist James Hartle predicted that if you go back to the beginning of the universe, the universe shrinks and closes off like a sphere. The new theory changes this.

“Now we’re saying that there is a boundary in our past,” said Prof Hertog.

They used their new theory to develop more reliable predictions about the global structure of the universe. They predicted that the universe emerging from eternal inflation on the past boundary is finite and far simpler than the infinite fractal structure predicted by the old theory of eternal inflation. If confirmed, their theory would have far-reaching implications for the multiverse paradigm.

Professor Stephen Hawking in March 2015. Picture: Andre Pattenden
Professor Stephen Hawking in March 2015. Picture: Andre Pattenden

“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 Prof Hawking.

This means the concept is more testable and Prof Hertog now plans to study its implications on smaller scales within reach of space telescopes.

He believes that primordial gravitational waves – ripples in spacetime – generated at the exit from eternal inflation constitute the most promising lead to test the model.

Due to the expansion of our universe, these gravitational waves have very long wavelengths, outside the range of current LIGO detectors. But they might be detected by the planned European space-based gravitational wave observatory, LISA, or seen in future experiments measuring the cosmic microwave background.

Professor Stephen Hawking was diagnosed with motor neurone disease in his early twenties and was given a few years to live. He died on March 14, 2018, aged 76. Picture: Andre Pattenden
Professor Stephen Hawking was diagnosed with motor neurone disease in his early twenties and was given a few years to live. He died on March 14, 2018, aged 76. Picture: Andre Pattenden

Read more

Stephen Hawking’s scientific legacy: Black holes, event horizons and an exit from eternal inflation

Could public telescope or black hole sculpture be installed to remember Professor Stephen Hawking?

Professor Stephen Hawking in March 2015 . Picture: Andre Pattenden
Professor Stephen Hawking in March 2015 . Picture: Andre Pattenden

Prof Gerry Gilmore of Cambridge’s Institute of Astronomy on Gaia’s astonishing 3D map of the galaxy

How University of Cambridge astronomers looked back 12.9 billion years - and detected motion in newborn galaxies

Cambridge astronomers help develop James Webb Space Telescope - the ‘world’s most magnificent time machine’

The funeral of Professor Stephen Hawking in pictures

Professor Stephen Hawking at a dinner in his honour at Gonville and Caius College to celebrate his 75th Birthday. Picture: Keith Heppell
Professor Stephen Hawking at a dinner in his honour at Gonville and Caius College to celebrate his 75th Birthday. Picture: Keith Heppell

Prof Stephen Hawking, his world and work in his own words

Professor Stephen Hawking dies at 76 and leaves an indelible legacy

Tributes to Prof Donald Lynden-Bell, of Cambridge’s Institute of Astronomy, who changed our understanding of the universe



COMMENTS
()


Iliffe Media does not moderate comments. Please click here for our house rules.

People who post abusive comments about other users or those featured in articles will be banned.

Thank you. Your comment has been received and will appear on the site shortly.

 

Terms of Comments

We do not actively moderate, monitor or edit contributions to the reader comments but we may intervene and take such action as we think necessary, please click here for our house rules.

If you have any concerns over the contents on our site, please either register those concerns using the report abuse button, contact us here.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies - Learn More