The big bang could be a normal event in the natural evolution of the universe that will happen repeatedly over incredibly vast time scales as the universe expands, empties out and cools off, according to two University physicists. “We like to say that the big bang is nothing special in the history of our universe,” said Sean Carroll, Assistant Professor in Physics. Carroll and Chen’s research addresses two ambitious questions: why does time flow in only one direction, and could the big bang have arisen from an energy fluctuation in empty space that conforms to the known laws of physics? The question about the arrow of time has vexed physicists for a century because “for the most part, the fundamental laws of physics don’t distinguish between past and future. They’re time-symmetric,” Carroll said. And closely bound to the issue of time is the concept of entropy, a measure of disorder in the universe. As physicist Ludwig Boltzmann showed a century ago, entropy naturally increases with time. “You can turn an egg into an omelet, but not an omelet into an egg,” Carroll said. But the mystery remains as to why entropy was low in the universe to begin with. The difficulty of that question has long bothered scientists, who most often simply leave it as a puzzle to answer in the future. Carroll and Chen have made an attempt to answer it now. Previous researchers have approached questions about the big bang with the assumption that entropy in the universe is finite. Carroll and Chen take the opposite approach.

“We’re postulating that the entropy of the universe is infinite. It could always increase,” Chen said. To successfully explain why the universe looks as it does today, both approaches must accommodate a process called inflation, which is an extension of the big bang theory. Astrophysicists invented inflation theory so they could explain the universe as it appears today. According to inflation, the universe underwent a period of massive expansion in a fraction of a second after the big bang.

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