Ripples in the microwave radiation afterglow left by the big bang reveal that the universe is at least 78bn light years across.
Researchers led by Neil Cornish, a physicist at Montana State University, think they have at least partially answered one of the most fundamental questions in cosmology: how big is the universe?
Until now, estimates ranged between 'as big as we can see' through to 'infinite', depending on which model of the universe you happened to be looking at at the time. This research clearly marks the lower limit, even if it doesn't rule out infinity.
According to Nature, a recent suggestion was that the universe was shaped like a soccer ball, 60bn light years across. Other suggestions include the idea that the univese is indeed quote small, but is wrapped round itself, so we can't easily spot the edges.
"In principle, it would not be ridiculous to see light from the Earth that has wrapped around the Universe, so we could see the Earth as it was when, say, life formed 4 billion years ago," Cornish told Nature.
He then set about looking for a young Earth out there, somewhere. But where to look? As far back as possible, is the answer, which meant looking at data from the Wilkinson Microwave Anisotropy Probe (WMAP). This can detect microwave radiation from the earliest days of the universe: just 379,000 years after the big bang.
In a small universe, light from the same source would arrive in the same place from different directions. This, the team calculated, would produce irregularities - hot and cold spots - in the radiation. The team found no spots, therefore, Cornish conlcudes, the universe is bigger than we can see with our equipment, and must be at least 78bn light years across.
He suspects it may be even bigger, and hopes closer inspection of the WMPA results will allow him to refine his calculations. This could push the universe's minimum size up to 90bn light years. ®