For nearly three decades now, it’s been clear that the expansion of the Universe is speeding up. Some unknown quantity, dramatically dubbed ‘dark energy’, is pushing the Universe apart. But the rate at which the Universe’s expansion is increasing – called the Hubble Constant – hasn’t yet been nailed down to a single number. In fact, there are multiple ways of measuring it. The problem is that these methods don’t agree with each other.
They each give different numbers, which is a confounding – and exciting – puzzle. It means there may be new physics to uncover, if we look carefully. This mystery is known as the Hubble tension, and it’s only becoming more intractable as measurement techniques become more precise