The advent of sensitive high-resolution observations of the cosmic microwave background radiation & their successful interpretation in terms of the standard cosmological model has led to great confidence in this model's reality The prevailing attitude is that we now understand the Universe & need only work out the details In this book Sanders traces the development & successes of Lambda-CDM & argues that this triumphalism may be premature The model's two major components dark energy & dark matter have the character of the pre-twentieth-century luminiferous aether While there is astronomical evidence for these hypothetical fluids their enigmatic properties call into question our assumptions of the universality of locally determined physical law Sanders explains how modified Newtonian dynamics (MOND) is a significant challenge for cold dark matter Overall the message is hopeful the field of cosmology has not become frozen & there is much fundamental work ahead for tomorrow's cosmologists