Close your eyes and let your mind drift into the quiet mystery of space and whether it ever ends. The universe has no physical edge—no wall, no border, no fence around the cosmos. Instead, it may be infinite, stretching on forever, or finite but curved back on itself like the surface of a sphere, with no boundary to reach. The part we can see is the observable universe, a sphere 93 billion light-years across, bounded only by the horizon of light that has had time to reach us since the Big Bang. Beyond that horizon, more galaxies await, forever out of sight. Let the gentle acceptance of this cosmic mystery carry you into a deep and restful sleep.