Plurality and the Big Bang
It is said that the big bang created space and time—they did not exist beforehand. Thus something existed (a “singularity”) before space and time existed; and it was some sort of empirical particular not an abstract entity. It is generally conceived as superhot plasma not yet differentiated into elementary particles. Now adjoin that idea to the Kantian principle that space and time are the basis of individuation for empirical particulars: there can only be a well-defined plurality of particulars if there is a spatiotemporal manifold in which these particulars are arrayed. Then we get the result that the universe at the time of the big bang was a singularity in this strong sense: it was, and could only be, a single unified entity. The conditions for plurality were not met in that early state of things: metaphysical monism prevailed of necessity. The big bang fragmented reality, taking it from unity to multiplicity, by dint of space and time. It created division. It gave the world parts. It allowed particulars to exist apart from each other.
So one thing we know about the universe before the big bang is that it was devoid of plurality. It was as the metaphysical monists conceive of reality today: a seamless whole. Some philosophers have thought that Kant’s noumenal world must be a unitary world, given that it is not subject to the categories of space and time (the conditions for plurality not being met in that world). Others have speculated that all minds must be fundamentally identical given that the mind is not a spatial entity (for what could their distinctness consist in but spatial separation?). Well, if the universe issued from a big bang that created space and time, then it too must have existed in a unitary form—as a single undifferentiated entity. We can therefore deduce that there had to be a singlesingularity: there could not have been a plurality of singularities each spawning a totality of discrete particulars. For these would have to exist separately in space and time, given that spatiotemporal separation is the ultimate basis for individual distinctness, and space and time did not exist until the big bang wrought them. The universe could not have resulted from a pair of singularities—no universe could, by Kant’s principle. They would have to be separated in space (if simultaneous) but there was no space at the onset of the big bang. Accordingly, there was just one big bang, and there had to be: the singularity was necessarily singular. 
This is a substantive piece of knowledge—a significant cosmological theorem. We know very little about the state of the universe before the big bang, but we do know that it was unitary in a very strong sense—there was no existing plurality of empirically particulars. Metaphysically, the universe was one. Plurality was a later offshoot of this underlying oneness—an emergent property rooted in a more basic reality. We might even say that reality is fundamentally singular, cosmologically speaking. Maybe the singularity comprised a unified field of force lacking particulate structure—not even consisting of matter in the sense we now conceive of it. Material plurality is a late development, a contingent offshoot: au fond the universe is undivided power (energy, oomph). This is a fact worth knowing, providing an insight into the nature of the universe before it was fragmented by that early explosion. There was an abrupt transition from the One to the Many—plurality emanating from unity. An undifferentiated whole shattered into pieces as space and time took shape. The old cosmic unity was gone: now the universe was a collection of separate particulars existing at a distance from each other. Before the big bang there was no room (literally) in the universe for distinct particulars–everything had to be jammed inextricably together as a single seamless entity. It is doubtful that we can even conceive of this reality, except in the most abstract and metaphorical terms, given that our minds have evolved to cope with a world of spatiotemporal plurality: but its general structure follows from basic cosmological principles. In creating space and time the universe brought forth plurality from unity. It broke the bonds of being. It changed the metaphysical structure of reality.