Leandros Perivolaropoulos

According to Einstein's theory, massive objects cause spacetime curvature, like a heavy ball warping a rubber sheet. As they accelerate, they create ripples — gravitational waves, akin to the circles from a stone dropped in a pond.

The universe is expanding faster and faster thanks to dark energy. But measurements of the rate give contradictory results. A new explanation: in the past, dark energy acted as a brake, slowing the galaxies' recession, and then switched to acceleration. Like a car that first rolls backward and then lunges forward.