Universe started with hiss, not bang

The Universe began not with a bang but with a low moan, building into a roar that gave way to a deafening hiss. And those sounds gave birth to the first stars.

Cosmologists do not usually think in terms of sound, but this aural picture is a good way to think about the Universe's beginnings, says astronomer Mark Whittle of the University of Virginia in Charlottesville. Whittle has reconstructed the cosmic cacophony from data teased out over the past couple of years from the high-resolution mapping by NASA's WMAP spacecraft of the cosmic microwave background radiation, the afterglow of the hot early Universe.

For those worried that you cannot have sounds in space, that is true today, but it was not so in the Universe's infancy. For perhaps its first million years, the Universe was small and dense enough that sound waves could indeed travel through it - so efficiently, in fact, that they moved at about half the speed of light.