The constituents of the universe include galaxies, planets, stars, cars, humans, leptons, bosons, and other particles. For the constituents of the universe to be uncaused that would mean it is metaphysically necessary. For something to be metaphysically necessary that means that it could not have failed to exist—it exists in every possible world.

For something to be self-caused it must be simultaneously antecedent to itself to produce itself as its own effect. But this contradictory. This would be akin to the ultimate bootstrapping trick.

Our last option is for the universe to be contingent. Something is contingent if and only if it is not necessarily false and not necessarily true. In other words, it might or might not have existed. We observe that some things in the universe are contingent—that is, it owes its existence to something else.