Initial energy of a spatially flat universe: A hint of its possible origin

The evidence for a Big Bang origin of the universe is truly compelling, though its cause remains a complete mystery. As the cosmic spacetime is revealed to us with ever-improving detail, however, we are beginning to refine the range of its possible initial conditions—at least within the framework of current physical theories. The universe, it seems, is spatially flat, and here we discuss in clear, straightforward terms why this trait implies a cosmos with zero kinetic plus gravitational energy, though apparently not zero total energy. Such an outcome has far reaching consequences because of the possibility that the universe may have begun its existence as a quantum fluctuation. Was this from "nothing," or perhaps a preexisting vacuum? A nonzero total energy would seemingly preclude the former scenario, but not necessarily the latter, though this would then raise the question of how a fluctuation with nonzero energy could have lived long enough, or classicalized, for us to see it 13.5 billion years later. The high-precision measurement of the universe's spatial curvature may thus constitute the first tangible piece of evidence impacting a possible quantum beginning.