In the first part of the talk, I will discuss the modern understanding of the basic structure of matter, emphasizing the precision, beauty, and weirdness of the description we've developed. I will emphasize specifically, the theme that what we ordinarily perceive as empty space is in fact a rich dynamical medium. I'll show movies and pictures of how this medium would look to us, if we had eyes that could resolve distances below 10^{-13} centimeters and times below 10^{-24} seconds. The all-pervasive universal medium determines the structure of matter as we know it. Indeed, our deepest understanding of particles (including protons and neutrons) conceives them as being no more and no less than the various possible long-lived disturbances of the universal medium. Their masses, quite literally, correspond to the frequencies at which the universal medium naturally oscillates. In this profound sense, they express the Music of the Void.

In the second part of the talk, I'll discuss recent astronomical discoveries which indicate that the forms of matter we've been familiar with, and are the basis of terrestrial physics, chemistry, and biology, contribute only 5% to the total mass in the universe. I'll describe the (few) known properties of the additional stuff, discuss how we're going about trying to figure out what it is, and outline some promising ideas about what it might be.