Neutrons, protons, and electrons—these are the basic building blocks of matter. But this kind of matter is only a tiny fraction of the entire universe. The rest, about 95 percent, in fact, is divided between dark matter and dark energy. Understanding what makes up dark matter and dark energy could help answer some of the biggest questions in physics. Physicists Jodi Cooley, Dan Hooper, and Nobel Prize winner Steven Weinberg join Ira Flatow to discuss what we do and don’t know about this “darker” side of physics, and what we hope to learn.