The Cambridge companion to atheism

[W]hy is there a whole of parts rather than nothing at all? […] The reason why this whole of parts exists, rather than some other possible whole, is that this whole’s existence is logically required by the existence of its parts, and its parts exist. The parts of the merely possible whole do not exist, and therefore the actual existence of this merely possible whole is not logically required.

But why these parts? These parts exist because all of them have been caused to exist by earlier parts. Other possible parts do not exist because nothing causes them to exist.

But why is there something rather than nothing? The whole of parts is something. The reason it exists is that every one of its parts has been caused to exist by earlier parts and the whole’s existence is logically required by the existence of the parts. The reason there is not nothing is that a universe caused itself to begin to exist and the basic laws governing this universe instantiated themselves.

By thy is there such a thing as a universe that causes itself to begin to exist? The reason is that this universe’s existence is logically required by the existence of its parts and its parts exist because each of them is caused to exist by an earlier part.