“This awareness, so unnerving against the backdrop of our irrepressible yearning for constancy and permanence, was first unlatched when the ancients began suspecting that the Earth, rather than being the static center of the heavens it was long thought to be, is in motion, right beneath our feet. But it took millennia for the most disorienting evidence of inconstancy to dawn — the discovery that the universe itself is in flux, constantly expanding, growing thinner and thinner as stars grow farther and farther apart. In 1929, the astronomer Edwin Hubble built on the work of other scientists and formalized this in what is now known as Hubble’s Law — the first observational evidence for the ongoing expansion of the universe, which in turn furnished foundational evidence for the Big Bang model: If the universe is constantly expanding, to trace it backward along the arrow of time is to imagine it smaller and smaller, all the way down to the seeming nothingness that banged into the somethingness within which everything exists.”