Jing-Fei Zhang

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.

At the center of a black hole lies a singularity — a point where spacetime is crushed infinitely. Black holes can change state, much like water freezing or boiling. Usually, these transitions are noticed by observing the hole's surroundings.

The Taiji detector, planned for launch into space, will pick up the trembling of space caused by collisions of enormous black holes. But its data is frequently marred by random bursts, like static crackling in a radio receiver.

Cosmology resembles a courtroom where two witnesses give irreconcilable testimonies. The first — the analysis of the cosmic microwave background by the Planck satellite — claims: the expansion of the universe proceeds at 67 (km/s)/Mpc.

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.

Ever since Einstein predicted gravitational lensing, and gravitational waves were first heard by LIGO detectors, physicists have dreamed of catching the lensed echo — a repeating signal from one merger, multiplied by the gravity of a massive body.