It all started with Einstein. A century ago, astronomers had a giant sandbox given to them in the form of Einstein’s theories, and they tried once and for all to explain the universe with them. Instead, they found even stranger phenomena waiting for them, all of which seemed to be driven by a mysterious form of matter. Just one problem: no one could actually find it. Welcome to the mystifying world of dark matter.

There is something enormous scattered throughout the universe—so, what could it be? Scientists are dissecting the underlying clues of dark matter and discovering that their investigation is becoming increasingly complex. Explore how the study of the smallest particles intersects with our understanding of the largest bodies in the universe. Strap on your helmet, as we need to go underground for this journey.

Where there are suspects, there’s a lineup. Physicists have started to define what exactly dark matter could be through a combination of computational modeling, hints from experiments, and some good old thinking outside the box. But that has produced a wide range of potential candidates for dark matter. So let’s ask: who are you, dark matter? What do you really look like, and what are you really up to?