Somewhere around 13.8 billion years ago, the Universe began with a bang. In less than a second, the four fundamental forces -- electromagnetism, gravitation, weak nuclear interaction, and strong nuclear interaction -- which initially were joined as a single even more fundamental force, separated. Suddenly, the Universe started to expand at an exponential rate. Cosmic inflation had begun. .... The Big Bang is the best theory we have to explain the birth and existence of the Universe. As astrophysicist Ethan Siegel wrote in his recent book Beyond the Galaxy: "To this very day, there is no other model that is...