Cosmology--the scientific study of the origin and evolution of the Universe--was revolutionized in the 20th century. This began with the observations by Hubble that the galaxies around us are in motion, and Einstein's relativity theory which taught us to understand this motion as the expansion of the Universe. Applying laboratory physics of atoms and nuclei, we will see how we can understand observations that trace the history of the early universe: how the whole cosmos was a primordial fireball, and at early stages was a vast nuclear reactor. Moving into the 21st century, we will see how astronomical observations also point to the existence of dark matter--the physics of which we don't yet understand, but could well be an indication of the existence of exotic elementary particles left over from the earliest times of the big bang. In these ways, we see that the Universe is the "poor man's accelerator," probing particle interactions at the highest laboratory energies and beyond.