Picture two metal cups, one nested inside the other with almost no gap between them. They hang in weightlessness inside a satellite orbiting the Earth. Waves of invisible matter, like gusts of wind, sweep through them constantly. These waves are so long that they engulf both cups at once, and then the cups start to tremble in unison.
When a wave passes through two objects, it behaves like light passing through two windows: bands of light and shadow appear on the floor. The same thing happens here: waves bouncing off the first cylinder mix with waves bouncing off the second, so in some places the trembling grows stronger and in others it almost vanishes. That is exactly the kind of trembling the scientists looked for in data from the MICROSCOPE satellite.
They found no clear signal, but that is not a failure: we now know that dark matter interacts with ordinary matter even more weakly than previously thought. And that knowledge will help build more sensitive instruments in the future.
The two MICROSCOPE cylinders are separated by a gap of just 1 centimeter, but for dark matter waves with a mass of 5×10⁻³ eV the coherence length is about 10 centimeters, which lets them interfere like light in Young's experiment.