Two metal cylinders hang inside a satellite almost without touching, with a finger-thick gap between them. Past them, like wind through window frames, streams a flow of invisible waves. This is dark matter, and it does not simply fly by: it makes the cylinders tremble ever so slightly, as if someone were drawing a bow across the strings stretched between them.

Earlier experiments of this kind caught dark matter with a single massive object, the way you catch a ball with one palm. But if the wave is long enough, it covers both cylinders at once, and then they start to behave like two windows that the same light passes through. Waves scattered off the first cylinder add to waves scattered off the second, reinforcing each other in some places and cancelling out in others. Physicists call this interference, and for dark matter it had never been observed.

The MICROSCOPE satellite rotates, and because of that the angle at which the wave strikes the cylinders keeps changing. The force acting on each cylinder changes too, and the difference between them oscillates at the rotation frequency. The scientists analyzed data from all the mission's sessions and found no significant signal, but they did establish new limits: the scattering cross section of dark matter on nucleons does not exceed 10⁻⁵² cm². That is two orders of magnitude tighter than before.

So two cylinders separated by a centimeter of emptiness have turned into an instrument that hears the faintest whisper of the Universe. And although it has not yet caught a voice, the very ability to listen is a step forward.