To COOK up planets, stars and people, the universe had to be preheated. In the first slivers of a second after the big bang, the universe expanded exponentially in a process called inflation, leaving the cosmos empty and cold. "Inflation is a flash-freezer," says John Giblin of Kenyon College in Gambier, Ohio. A few minutes later, energetic photons were zipping through a dense cauldron of radiation at a searing 1010 kelvin, the first stage in a cascade of events that gave rise to the matter we have today. So where did all the heat come from?
The energy that drove inflation is one option, but it would have been trapped in a field when the process ended. In the 1980s, physicists suggested that this "inflaton field" decayed into radiation, infusing the universe with heat. But models show the process would have been too slow to make all the matter we see.
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