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We've known that the universe is expanding since 1929, and that its expansion is accelerating since 1998. The culprit behind the acceleration is unknown, so we live with a stand-in term "dark energy". Our modern cosmological model assumes that dark energy has a constant density--always the same amount of the outward-shoving stuff per volume. But there's recent evidence to the contrary--which may be why our primary efforts to measure the expansion rate of the universe disagree with each other.

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Hosted by Matt O'Dowd

Written by Matt O'Dowd

Post Production by Leonardo Scholzer

Directed by Andrew Kornhaber

Associate Producer: Bahar Gholipour

Executive Producer: Andrew Kornhaber

Executive in Charge for PBS: Maribel Lopez

Director of Programming for PBS: Gabrielle Ewing

Assistant Director of Programming for PBS: Mike Martin

Spacetime is a production of Kornhaber Brown for PBS Digital Studios.

This program is produced by Kornhaber Brown, which is solely responsible for its content.

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End Credits Music by J.R.S. Schattenberg: https://www.youtube.com/user/MultiDroideka

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