Hannah Devlin in The Guardian:
Cosmologists don’t enter their profession to tackle the easy questions, but there is one paradox that has reached staggering proportions.
Since the big bang, the universe has been expanding, but the known laws of physics suggest that the inward tug of gravity should be slowing down this expansion. In reality, though, the universe is ballooning at an accelerating rate.
Scientists have come up with a name – dark energy – for the mysterious agent that is allowing the cosmos to expand so rapidly and which is estimated to account for 70% of the contents of the universe. But ultimately nobody knows what the stuff actually is.
“It’s the big elephant in the room,” says Prof Claudia de Rham, a theoretical physicist at Imperial College. “It’s very frustrating.”
Change could be afoot.