Dark energy dominates the universe, and could lead it to a cold, bleak end. But that’s not to say we have much clue what it is or how it works
DARK energy is everywhere – and when we say everywhere, we mean everywhere. It suffuses every corner of the cosmos, absolutely dominating everything in it. It dictates how the universe behaves now and how it will end. What a pity, then, that we have no clue what it is.
It exploded onto the scene in 1998, when two competing groups made the same observation of distant supernovae. These massive stellar explosions were further away than their brightness suggested they should be, indicating not just that the universe is expanding, which was expected, but that its expansion is accelerating, which wasn’t.
About the best we can do is say that dark energy acts as a kind of antigravity, pushing things apart where gravity pulls them together. Dark energy’s inscrutability earned it its name, but Catherine Heymans at the University of Edinburgh, UK, isn’t a fan. “When most people think of something as being dark, they think of it as absorbing light,” she says. “Dark energy doesn’t absorb or emit light.”
“Dark energy is a weird perpetual motion machine”
Be that as it may, it makes up a whopping 68 per cent of all the universe’s matter and energy. Regular matter makes up less than 5 per cent. The remainder is almost equally inscrutable, but gravitating, dark matter.
Most cosmologists think dark energy is spread out across the universe with equal density, like butter perfectly smeared on a slice of toast. That would mean more of it is created to fill new space as the universe expands, says Heymans. “It’s a weird …