The orchestra plays, but the conductor hears only a general hum. Each instrument plays its own part, but you can't tell where the flute is and where the double bass is. You need a spectrum analyzer — a device that breaks down sound by frequency. In astronomy, the same problem exists: cold interstellar dust and gas emit at millimeter and submillimeter wavelengths, and to understand their composition and motion, you need to split that light into a spectrum.

The new instrument, SWISS, is such an analyzer, but for light. It looks like a tiny maze carved into a stack of silicon wafers. Light enters an antenna that splits it into two polarizations (two directions of wave oscillation), then passes through a series of tiny resonant cavities. Each cavity is tuned to its own frequency, like a guitar string to its note. When light matches the cavity's frequency, it lingers and is transferred to a sensitive detector, so spectroscopy becomes precise and compact.

The key trick is in the stacking. Usually, such filters are arranged in a single plane, making the device as wide as a pancake. Here, the filters are turned perpendicular, and the output signal is bent in a smooth curve, so engineers packed the maximum number of channels into a minimal volume. The whole structure is assembled from silicon wafers, etched with deep reactive ion etching (like burning a pattern with a laser, but at the atomic level) and coated with metal. A prototype is already being tested, including an antenna transition without mechanical contact — light jumps from the antenna into the waveguide through a metamaterial, as if over an invisible bridge.

Such a spectrometer can be mounted on a space telescope or in a network of ground-based antennas. It will help see how stars are born in dense clouds of cosmic dust, and how galaxies move on the outskirts of the expanding universe. The cosmic orchestra will finally play by the notes.