Each of these two forms of the cosmological argument, then, evades the objection introduced above in a distinct way. The first does so by distinguishing between things that have a beginning in time and things that do not. The second does so by distinguishing between things that are contingent and things that are necessary. In each case it is argued that the universe is of the former kind, that God is of the latter kind, and that the principle that everything has a cause applies only to things of the former kind, and therefore not to God.
Philosopher Quentin Smith has cited the example of virtual particles , which appear and disappear from observation, apparently at random, to assert the tenability of uncaused natural phenomena.  In his book A Universe from Nothing: Why There is Something Rather Than Nothing , cosmologist Lawrence Krauss has proposed how quantum mechanics can explain how space-time and matter can emerge from "nothing" (referring to the quantum vacuum). Philosopher Michael Martin has also referred to quantum vacuum fluctuation models to support the idea of a universe with uncaused beginnings. He writes:
Central to Thomism – the life work of St. Thomas Aquinas (1225 – March 7, 1274) is the idea that Philosophy can help us come to a better understanding of Theology – the study of God. Aquinas thus asked the question: is it obvious that there is a God? His answer was no – since such a concept is beyond all direct human experience. He then asked the question: can it be made obvious? Aquinas believed that, since the universe is God's creation, evidence of God's existence can be found in his creation using intellect and reason. Aquinas therefore devised his 'Five Ways,' five a posteriori proofs for the existence of God based on our empirical experience of the universe.