  Our understanding of ordinary matter is remarkably accurate and complete, but
it is based on principles that are very strange and unfamiliar. As I'll
explain, we've come to understand matter to be a Music of the Void, in a
remarkably literal sense. Just as we physicists finalized that wonderful
understanding, towards the end of the twentieth century, astronomers gave us
back our humility, by informing us that ordinary matter -- what we, and
chemists and biologists, and astronomers themselves, have been studying all
these centuries constitutes only about 5% of the mass of the universe as a
whole. I'll describe some of our promising attempts to rise to this challenge
by improving, rather than merely complicating, our description of the world.
