How did the universe start? Did we begin with a big bang, or was there a bounce? Might the cosmos evolve in a cycle of expansion and collapse, over and over for all eternity? Now, in two papers, researchers have poked holes in different models of a so-called bouncing universe, suggesting the universe we see around us is probably a one-and-done proposition.
Bouncing universe proponents argue that our cosmos didn’t emerge on its own out of nothing. Instead, advocates claim, a prior universe shrunk in on itself and then regrew into the one we live in. This may have happened once or, according to some theories, an infinite number of times.
So which scenario is correct? The most widely accepted explanation for the history of the universe has it beginning with a big bang, followed by a period of rapid expansion known as cosmic inflation. According to that model, the glow left over from when the universe was hot and young, called the cosmic microwave background (CMB), should look pretty much the same no matter which direction you face. But data from the Planck space observatory, which mapped the CMB from 2009 to 2013, showed unexpected variations in the microwave radiation. They could be meaningless statistical fluctuations in the temperature of the universe, or they might be signs of something interesting going on.
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