Birth Of The Universe

The universe went through a traumatic growth spurt before it was a billionth of a billionth of a second old, according to the latest data from the Wilkinson Microwave Anisotropy Probe (WMAP). The WMAP team revealed the best map ever drawn of microwaves from the early universe, showing variations in the brightness of radiation from primordial matter. The pattern of these variations fits the predictions of a physical theory called Inflation. The variations in the density of matter that the microwave map shows up were created by quantum fluctuations during the expansion and those fluctuations provided the seeds for the gravitational growth of galaxies and stars .

Quantum giants

Astronomers thought that ionised gas created by the first generation of stars might be mimicking the imprint of inflation by scattering the microwaves on their way to us from distant parts of the universe.

Now the team say not. With three years of data instead of one, they have been able to map not just the brightness but also the polarisation of cosmic microwaves. The polarisation reveals just how much the waves have been modified by bouncing off ionised gas. After subtracting that effect from the temperature map, the team still find that inflation fits the pattern. It predicts that larger clumps in the background are brighter than smaller clumps, just as the data show. This is the strongest evidence so far in support of inflation. "Galaxies are nothing but quantum mechanics writ large across the sky," says ESA member Greene at Columbia University, New York, US.

Profound implications

So what force could actually have caused inflation? There have been hundreds of speculative physical models, postulating as yet unknown energy fields. But the new data are precise enough to rule out many of these ideas – especially some of the more complicated ones. "The simplest of the models fits the data well," says WMAP member David Spergel at Princeton University, New Jersey, US.

If either WMAP or ESA's upcoming Planck satellite can detect a gravitational-wave signal, physicists will begin to learn why inflation happened, and that could have profound implications for fundamental physics.

The WMAP data suggested that the first stars started ionising gas after only 200 million years, seemingly leaving too little time for gas to gather into clumps and make stars. The new data show it did not happen for 400 million years – a long age of darkness, and plenty of time for the first stars to form.