— YOU would think that right after the big bang, the universe would have been pretty hot. In fact it looks like things were a lot cooler than you might imagine.
Cosmologists believe that the universe went through a rapid period of expansion known as inflation. But, says Pedro Ferreira at the University of Oxford, they usually ignore the effects of temperature on inflation - and that's a big mistake. "At the violent temperatures we assume are around at the time, everything would be moving rapidly," he says. "Space-time itself would be bubbling and boiling."
Ferreira and João Magueijo, currently at the Perimeter Institute in Waterloo, Canada, realised that any such thermal "noise" would have been amplified during inflation. If the noise had been too loud, it would have disrupted the formation of galaxies and left behind huge imprints on the cosmic microwave background today.
Because we don't see such imprints, while we do see large galaxies and clusters, we have a clue to the temperature of the early universe, says Ferreira. The pair calculated that at the end of inflation, 10-32 seconds after the big bang, the maximum temperature would have been about 11,000 °C (www.arxiv.org/abs/0708.0429). "That's extremely cool - not the zillions of degrees you'd expect," says Magueijo.