The expansion rate of the universe, or the Hubble constant, is determined by two routes, like dough: you measure its height now (supernovae and galaxies) or you calculate from the ancient glow, the relic radiation from the Big Bang era. But the numbers don't match: that's the Hubble tension. Curiously, Edwin Hubble, who discovered the expansion, didn't trust his own result, and his first measurement turned out seven times higher than the true value.

The DESI instrument, breaking down the light of millions of distant galaxies by color (spectroscopy), stumbled upon a surprise: a key ingredient, dark energy, seems to have changed strength. If it's not a glitch, then old calculations based on the relic radiation need a correction. With that, the estimates of Adam Riess, long considered too high, become accurate.

So the yeast in the cosmic dough turns out to be sometimes more active, sometimes less. The ancient light, first captured by Arno Penzias, tells not just of expansion, but of the changing nature of the void. Add to that dark matter (an invisible skeleton, five times more abundant than ordinary matter) and the recipe for the universe looks far more complex than it seemed.