If you’ve ever read anything about cosmology, you’ll have come across an astonishing statistic: all the matter around us, everything we see and touch, every star and gas cloud and planet, makes up just five per cent of the energy in the Universe.

Of everything else, around 25 per cent is made up of dark matter, and the rest – a baffling 70 per cent of everything that exists – is dark energy.

Cosmologists say this must be the case because of the way the Universe is expanding. But it isn’t just that the Universe is expanding; it’s that the expansion is accelerating, and something must be driving that. We call that unknown force dark energy.

Read more: ‘If I’m wrong, I can retire’: Why some physicists are now betting big that dark energy doesn’t exist (another what kept them?)