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PBS Space Time

Dark Energy Is Driving the Universe Apart. We May Finally Know Why.

Season 11 Episode 22

We’ve known since 1929 that the universe is expanding, and since 1998 that it’s speeding up. The unknown force behind this acceleration is called “dark energy,” assumed to stay constant in density. But new evidence hints it may change over time, possibly explaining why major measurements of the universe’s expansion rate don’t agree.

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