Dawkins has complained that if theists are allowed to posit the necessary existence of God, then he ought to be allowed to posit necessary existence of the cosmos. There are two problems with this. First, theists do not begin with some arbitrary concept, x and then add on necessary existence. Their reasoning, rather, is that necessary existence is part of the existence of God. If someone were to report, “Oh, God existed at noon today and then perished at 2:00 PM,” we would normally think the person is joking. The concept of God simply is the concept of a being that cannot be vulnerable to nonexistence. Second, there does not appear to be anything in the cosmos or about the cosmos that involves necessary existence. The fact that science must observe the world in order to explain it is evidence that world could have been different. The concept of the cosmos is contingent; various scientific theories explaining the way that the world works may have conditional necessity (a quark must have a certain electric charge, given the prevailing laws of physics), but nothing in or about the cosmos is essentially necessarily existent, nor are the laws of physics themselves necessary. There are current laws of the conservation of energy, but none of them provides any reason to think that energy itself necessarily exists. The mere endurance of some force or event over time, even if it is without beginning, does not itself constitute necessary existence.
Charles Taliaferro and Elsa J. Marty “The Coherence of Theism” in Contending with Christianity’s Critics (B&H Academic 2009), page 188.