To study the origins of our universe is to struggle with profound chicken-or-egg questions. We know the Big Bang happened. Cosmologists can see its afterglow in the sky. But no one knows whether the laws of physics or even time itself existed before that moment. Nor can we say exactly what happened next. The order in which certain celestial objects formed during the very early universe is hotly contested. For a long time after the Big Bang, not much of anything could form. All of space was permeated by a roiling plasma. It was too hot and chaotic for any structure to cohere. Hundreds of thousands of years passed before a tiny hydrogen atom could even hold itself together. Another 100 million years or so after that, great clouds of hydrogen condensed and stars flared into being. Most cosmologists believe that these stars were the first large, free-floating structures to illuminate our universe, and that black holes appeared later. But some have proposed that it went the other way...
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