To Infinity and Beyond: The Accelerating Universe

Dark energy is cosmology’s biggest mystery—an anti-gravitational force that confounds the conventional laws of physics. It makes up more than two-thirds of the cosmos, but science is still grappling to explain what dark energy actually is. In this program, top physicists search for clues to this mystery in both the earliest moments of the universe and far into the future of the cosmos.

Photograph: Jon Smith

The Big Ideas series is supported in part by the John Templeton Foundation.

Our media partner for this program is Mental Floss.

Why are Tattoos Permanent?

If you don’t have a tattoo, you probably at least know someone who does — but what’s the chemistry behind tattoos? In this Reactions video we explore what tattoo ink is made of, why this body art is permanent (whether you like it or not) and other cool facts.

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For more information on tattoos, check out Claudia Aguirre’s article:­ealth