Cosmic surveys suggest the force pulling the universe apart might not be constant after all

Imagine sitting in the center of a firework that has just exploded. After the first flash of light and heat, sparks fly off in all directions, with some streaming together into fiery filaments and others fading quickly into cold, ashy oblivion. After a moment more, the smoke is all that remains—the echo, if you will, of the firework’s big bang.

Now imagine the firework is the universe, which scientists think began with a similar explosion. Where the firework’s expansion is propelled by a chemical reaction, the expansion of the cosmos comes from the energy of empty space itself. From where we sit, it seems that the universe is expanding in all directions, faster and faster at every moment.

This spring scientists announced that something is wrong with the fireworks. For the first time since the discovery of dark energy—the mysterious force that is accelerating our cosmic fireworks show—cosmologists think we may be on the cusp of something new. Two prominent dark energy surveys seeking to measure the nature of this force found evidence that dark energy seems to have weakened over time.