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.
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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 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 perpetual motion machine.” That suggests a bleak future for the universe if dark energy’s dominance continues: pushed ever further apart, galaxies will eventually lose sight of one another, lost in uniform dull blackness.
One popular way to explain where dark energy comes from is to invoke quantum theory. Random, small-scale quantum effects create energy even in the vacuum of empty space – so the more space, the more energy. But when you calculate the amount of this quantum dark energy there should be, “you get it wrong”, says at Utrecht University in the Netherlands. And not just by a little – by a factor of 10120.
Maybe. Recent observations of the universe’s expansion have shown that, when you use standard cosmic models to extrapolate the early universe’s expansion rate to the present day, the predicted value falls far short of what we actually measure. One explanation could be that dark energy is more complicated than we thought. “You get into all kinds of exciting, glorious models,” says Heymans – ones where dark energy evolves with time, for example, or interacts with dark matter in mysterious ways.
Or maybe not – with dark energy, we just can’t tell, says Heymans. “It could be that we’ve got everything wrong.”
Cutting-edge science throws up all sorts of controversial, nebulous and mind-bending concepts. Here’s your guide to how to think about some of the fiddliest of them:
- In the quantum world, uncertainty reigns – or is it all in the mind?
- Think you understand how evolution works? You’re probably wrong
- Why information could be our route to the universe’s deepest secrets
- Who do you think you are? Why your sense of self is an illusion
- Homo sapiens? Genetic insights suggest we may not really be a species
- Big bang retold: The weird twists in the story of the universe’s birth
- Firms and governments use the internet to spy on us. Should we care?
- D’oh! Why human beings aren’t as intelligent as we think
- Extinction is a fact of life. Could we stop it – or even reverse it?
- No more goody two shoes: Why true altruism can’t exist
- Alien life could be weirder than our Earthling brains can ever imagine
- Why it’s time to call time on the ‘nature vs nurture’ debate
