Astronomers believe that matter in intergalactic space is distributed in a vast network of interconnected filamentary structures known as the cosmic web. Nearly all the atoms in the Universe reside in this web, vestigial material left over from the Big Bang. A team led by researchers from the Max Planck Institute for Astronomy in Heidelberg have made the first measurements of small-scale fluctuations in the cosmic web just 2 billion years after the Big Bang. These measurements were enabled by a novel technique using pairs of quasars to probe the cosmic web along adjacent, closely separated lines of sight. They promise to help astronomers reconstruct an early chapter of cosmic history known as the epoch of reionization.