The Universe is structured like a sponge: there are dense regions packed with galaxies and gas, and giant pores — cosmic voids. These voids occupy most of space, but their contents have remained a mystery because matter there barely reveals itself.

Now astronomers have 'felt' the voids using fast radio bursts — super-powerful pulses from distant galaxies. As these pulses travel through the pores, they slow down slightly when they encounter stray electrons — tiny charged particles lingering in the gas. It's like water losing speed as it flows around sponge fibers. By measuring the delay in thousands of such bursts, scientists have weighed the invisible gas for the first time, mostly hydrogen.

Paradox: this gas is heated to a million degrees, but due to its incredibly low density, it barely transfers heat. If you were inside a void, you'd freeze, not burn. Studying these voids is crucial: they let us investigate dark energy and the properties of nearly elusive neutrinos, refining models of the expansion of the Universe.