By studying exploding stars, an Australian astrophysicist and his colleagues worked out that the Universe is not just expanding, but expanding faster and faster, thanks to dark energy. They pretty much single-handedly made us realise that instead of a Big Crunch, the Universe is just going to… gradually dissipate. Woah. We asked science writer Niall Byrne to talk us through the mind boggliness of it all.
Yesterday morning the Nobel Prize for Physics committee sat down in Stockholm to consider the 2011 prize. By noon they had decided to give the prizes to the leaders of two teams of reseachers who together had come up with a crazy result that broke our understanding of the nature of the Cosmos – that our Universe is expanding at an accelerating rate.
An accelerating universe was a crazy result that was hard to accept. Yet, two teams, racing neck and neck, simultaneously came to the same conclusion. Their discovery led to the idea of an expansion force, dubbed dark energy. And it suggests that the fate of the universe is to just keep expanding, faster and faster.
Thanks to Brian Schmidt, Saul Perlmutter, Adam Riess and their colleagues we now know that the stars, dust and galaxies that we can see in the sky comprise just 5 per cent of the Universe; 25 per cent is dark matter, and the rest is something else that’s pushing the Universe apart. Cosmologists call it dark energy, though no one has actually seen it yet.
And the hunt for this dark energy has engaged hundreds of astronomers worldwide.
Brian Schmidt, from the Australian National University led one of the teams competing to determine the fate of the Universe. They expected to discover that it would either expand then contract, or it would expand for ever but slow over the millennia. But there were a growing number of hints that all was not right with the theories of the time.
To find out, they not only needed to be able to measure the speed with which distant objects are traveling away from us, but also how far away they are. And to do this they needed standardised light sources — very bright ones that would be visible to Earth-based telescopes despite being billions of light years away and billions of years old.
The standard light sources they used were exploding stars — in particular Type 1a supernovae. But finding them wasn’t easy. Then the analyses over the results turned up very surprising results.
“The data wasn’t behaving as we thought it would,” says Schmidt. “There was a lot of nervous laughter,” says Perlmutter.
For both teams it was not what they were expecting. For months they both tried to figure out where they had gone wrong, searching for any tiny source of error. But the data was right. The accepted model of the universe was wrong.
The initial response of the astronomy community was one of shock, but it quickly changed to acceptance. The research was impressively rigorous, and the unanimity between the teams’ results was very convincing. It just made the universe work, cosmologically speaking. A few attempts were made to try to propose alternative explanations for the results, but they were quickly abandoned.
Both Perlmutter and Schmidt are quick to point out that, while team leaders often get all the credit, in both cases it really was a full team effort. Many individuals from different institutions all around the world worked on the problem.
Where to from here?
The upshot of the teams’ work is this: The total matter/energy balance of the universe is believed to be composed of only 5 per cent normal matter, and around 25 per cent dark matter, with the other 70 per cent attributed to the expansion force, which has been dubbed ‘dark energy’.
Having worked out that the expansion is accelerating, and that dark energy exists, the challenge now is to determine what exactly dark energy is.
One solution is to bring back Einstein’s cosmological constant, as a force that pervades space and acts in the opposite way to gravity - a repulsion effect that makes the universe want to spread out. This is a leading candidate.
A variation on this theme is something called ‘quintessence’, a similar force but one that might change with time (as opposed to the cosmological constant, which would remain unchanged no matter how big or old the universe became).
And a new generation of telescopes are being built to attempt to answer the question.
Schmidt has developed the SkyMapper project, a telescope to map the southern sky, finding more supernovae faster. Perlmutter is working on a satellite mission that would study supernovae and the nature of dark energy.
And Australia is bidding to become the home of the Square Kilometre Array, a $2 billion radio telescope that will be built either in South Africa or in a remote and radio quiet corner of Western Australia. One of its missions will be the search for dark energy.
But there is another possibility, one that many scientists find disturbing. Maybe there is no such thing as dark energy. Perhaps it is our understanding of gravity that is faulty.
If gravity doesn’t behave the way we think it does over very large distances, or if it has changed its nature at different stages of the Universe’s history, then maybe Einstein’s General Theory of Relativity needs replacing or modifying. But General Relativity has stood up against every test thrown at it so far, so to most scientists the idea that it might need changing is something that makes them very uncomfortable. Yet the possibility cannot be ignored.
So could it be that, having already overturned one long-cherished astronomical concept with their research, the two teams’ 1998 findings will lead to the overturning of another?
Only time will tell.
Niall Byrne is a science writer with Science in Public, a Melbourne-based team of science communicators.
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