The universe is made up of much more than meets the eye. While telescopes reveal countless galaxies, each containing billions of stars, physicists and astronomers believe that visible matter is just the tip of the iceberg, so to speak, and that some kind of unseen dark matter must be out there as well, accounting for some 85 percent of the mass of the universe. No one knows what dark matter is made of, but scientists are confident it’s something that doesn’t interact with electromagnetic radiation, such as light—or else we’d be able to see it. But decades of searching have failed to yield any direct detections of this dark matter, leaving researchers wondering if they need to broaden their search strategies, or perhaps even rethink how gravity works.