Did the Universe Boot Up with a “Big Bounce?”

Did the universe start with a bang or a bounce—or something else entirely? The question of our origins is one of the thorniest in physics, with few answers and lots of speculation and strong feelings. The most popular theory by far is inflation, the notion that the cosmos blew up in size in the first few fractions of a second after it was born in a bang. But an underdog idea posits that the birth of this universe was not actually the beginning—that an earlier version of spacetime had existed and contracted toward a “big crunch,” then flipped and started expanding into what we see today. Now a new study suggesting a twist on this “bounce” scenario has supporters excited and inflation proponents newly inflamed over a “rival” they say they have repeatedly disproved, only to have it keep bouncing back.