WHAT IS THE NATURE OF THE UNIVERSE AND WHAT IS IT MADE OF? WHAT ARE MATTER, ENERGY, SPACE AND TIME? HOW DID WE GET HERE AND WHERE ARE WE GOING?
	The quest to answer the most basic questions about the universe has reached a singular moment. As the 21st century begins, physicists have developed a commanding knowledge of the particles and forces that characterize the ordinary matter around us. At the same time, astrophysical and cosmological space observations have revealed that this picture of the universe is incomplete-that 95 percent of the cosmos is not made of ordinary matter, but of a mysterious something else: dark matter and dark energy. We have learned that in fact we do not know what most of the universe is made of. Understanding this unknown “new” universe requires the discovery of the particle physics that determines its fundamental nature. Powerful tools exist to bring the physics within reach. With astrophysical observations, we can explore the parameters of the universe; with accelerator experiments we can search for their quantum explanation. Energies at particle accelerators now approach the conditions in the first instants after the big bang, giving us the means to discover what dark matter and dark energy are-and creating a revolution in our understanding of particle physics and the universe. To answer the fundamental questions about the nature of the universe, astrophysical observations of the relics of the big bang must agree with data from physics experiments recreating the particles and forces of the early universe. The two ends of the exploration must meet. We will answer these challenging questions by combining what we learn from the most powerful and insightful observations and experiments in each of these approaches. The following chapters take up in successively greater depth nine key questions that defi ne the field. Chapter II elucidates the meaning of the questions and their implications for 21st century particle physics; Chapter III defines the scientific program to address and answer them. The tables in Chapter V summarize the U.S. facilities whose primary physics programs respond most directly to the questions. Proceed to "EINSTEIN"S DREAM OF UNIFIED FORCES"