For all we understand about the universe, 96% of what’s out there still has scientists in the dark. Astronomical observations have established that familiar matter—atoms—accounts for only 4% of the weight of the cosmos. The rest—dark matter and dark energy—is invisible to our telescopes. But what really is this dark stuff? How do we know it’s there? And what does it do? From the formation of galaxies to the farthest reaches of space, it appears that darkness rules. Without dark matter and dark energy, the universe today and in the far future would be a completely different place. We were joined by leading researchers who smash together particles, dive into underground mines, and explore the edges of the known universe in search of clues to nature’s dark side.