What is Dark Energy? Inside our accelerating, expanding Universe

11 min read What is Dark Energy? Inside our accelerating, expanding Universe Some 13.8 billion years ago, the universe began with a rapid expansion we call the big bang. After this initial expansion, which lasted a fraction of a second, gravity started to slow the universe down. But the cosmos wouldn’t stay this way. Nine billion years after the universe began, its expansion started to speed up, driven by an unknown force that scientists have named dark energy. But what exactly is dark energy? The short answer is: We don’t…

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