Guo-Hong Du

The Universe is expanding faster and faster. We used to chalk that up to dark energy — a mysterious force working alone. But the latest measurements seem to have eavesdropped on a private conversation: it appears dark energy is not silent but whispering back and forth with dark matter.

Light from distant galaxies passes through clumps of matter, and the gravity of those clumps slightly bends its path, like a lens. By measuring how much the images of distant galaxies are distorted, we can infer the distribution of matter and how gravity affects light.

Since the late 20th century, astronomers have known that the recession of galaxies is accelerating, as if pushed by an invisible tailwind.

For decades, two independent methods of measuring the rate at which galaxies are flying apart, the Hubble constant, have given conflicting numbers. The situation resembled a room with two thermometers showing different temperatures.