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Traditional Big Bang theory posits that our universe began with a singularity — a point of infinite density and temperature whose nature is difficult for our minds to grasp. However, this may not accurately reflect reality, researchers say, because the singularity idea is based on Einstein's theory of general relativity. "The problem is, there's no reason whatsoever to believe general relativity in that regime," said Sean Carroll, a theoretical physicist at Caltech. "It's going to be wrong because it doesn't take into account quantum mechanics. And quantum mechanics is certainly going to be important once you get to that place in the history of the universe." So the very beginning of the universe remains pretty murky. Scientists think they can pick the story up at about 10 to the minus 36 seconds — one trillionth of a trillionth of a second — after the Big Bang. At that point, they believe, the universe underwent an extremely brief and dramatic period of inflation, expanding faster than the speed of light. It doubled in size perhaps 100 times or more, all within the span of a few tiny fractions of a second. [The Big Bang to Now in 10 Easy Steps] (Inflation may seem to violate the theory of special relativity, but that's not the case, scientists say. Special relativity holds that no information or matter can be carried between two points in space faster than the speed of light. But inflation was an expansion of space itself.) "Inflation was the 'bang' of the Big Bang," Filippenko told SPACE.com "Before inflation, there was just a little bit of stuff, quite possibly, expanding just a little bit. We needed something like inflation to make the universe big." This rapidly expanding universe was pretty much empty of matter, but it harbored huge amounts of dark energy, the theory goes. Dark energy is the mysterious force that scientists think is driving the universe's current accelerating expansion. During inflation, dark energy made the universe smooth out and accelerate. But it didn't stick around for long. "It was just temporary dark energy," Carroll told SPACE.com. "It converted into ordinary matter and radiation through a process called reheating. The universe went from being cold during inflation to being hot again when all the dark energy went away." Scientists don't know what might have spurred inflation. That remains one of the key questions in Big Bang cosmology, Filippenko said.
