PHYSICS APPLECART UPSET as dark energy disappears, Universe slams on brakes

In-the-dark astrophysicists now think there's probably less dark energy knocking about than was previously thought – which may suggest that the universe is expanding at a slower rate.

That's at least the latest thinking on the subject to come out of the University of Arizona, whose team of astronomers claimed that their studies, published in the Astrophysical Journal, had "big cosmological questions" about how quickly the universe had accelerated since the Big Bang happened roughly 14 billion years ago.

The boffins discovered that the type of supernovae, which has been commonly used to supposedly measure reliable distances in the universe, fell into different populations that had not been spotted before now.

Astronomer Peter A Milne, who led the team at UA, found that the amount of light observed in type Ia supernovae varied more than had been previously theorised. The researchers collected the data using NASA's Swift, which examines gamma-ray bursts in the sky.

"The findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness," said the university's staff.

Milne explained:

We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances – and thus when the universe was younger.

There are different [red and blue] populations out there, and they have not been recognised. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn't appear to be the case.

It could mean that the scientific community's fuzzy thinking on dark energy may unravel even more, because the latest findings claim that the universe is not expanding faster and faster as textbooks on the topic currently suggest.

Back to Milne, who – alongside his team – observed a big sample of type Ia supernovae in ultraviolet and visible light and combined datasets from the Swift satellite and Hubble's space telescope:

The idea behind this reasoning is that type Ia supernovae happen to be the same brightness – they all end up pretty similar when they explode. Once people knew why, they started using them as mileposts for the far side of the universe.

The faraway supernovae should be like the ones nearby because they look like them, but because they're fainter than expected, it led people to conclude they're farther away than expected, and this in turn has led to the conclusion that the universe is expanding faster than it did in the past.

The boffins claimed that their findings could show that theories about the acceleration of the universe had been overblown.

"We're proposing that our data suggest there might be less dark energy than textbook knowledge, but we can't put a number on it," said Milne. "Until our paper, the two populations of supernovae were treated as the same population. To get that final answer, you need to do all that work again, separately for the red and for the blue population."

However, the research failed to pinpoint what such results could mean for the current measures of dark energy – which theorises that the universe is made up of 73 per cent of the stuff. Any attempt at re-working those numbers will involve yet more observations, apparently. ®