It may be a cliche, but it’s true: If at first you don’t succeed, try, try again. That’s certainly the case for the scientists hunting for dark matter. They’ve conducted many big experiments over the past few decades. So far, though, they haven’t found a thing. So the hunt is going smaller — looking for extremely light particles known as axions.

Astronomers see the effects of dark matter all across the universe. The dark matter itself emits no energy, but its gravity pulls on the visible matter around it. Measuring the mass of that gravitational effect shows that there’s about five times more dark matter than normal matter.

For a long time, the leading theory of dark matter said it was made of WIMPs — weakly interacting massive particles. Such particles would be much heavier than the protons and neutrons that make up normal matter. Physicists have built detectors to look for WIMPs. The detectors are far underground, so other types of particles are filtered out. But the experiments have come up empty.

So in the past few years, the search has begun turning toward axions. If they exist, they’d be billions of times less massive than electrons, which are by far the puniest parts of atoms. As with WIMPs, axion detectors are far underground. The University of Washington has been operating one for years. And a group in Europe is just getting cranked up. So the search for most of the mass in the universe is going small.

Script by Damond Benningfield