The cosmological argument attempts to infer the existence of God from general facts about the world . The most typical is the "first cause" argument, that does so based on the fact that everything has a cause. There must, the first cause argument says, be something that is the first cause, since an infinite chain of causes leaves everything without a cause. This first cause is assumed to be God.
There is also a specific form known as the kalam argument, which argues from the fact that the universe had a beginning. A more technical review of some cosmological arguments can also be found in the Cosmological Arguments entry.
The argument runs like this:
- Everything that exists must have a cause.
- If you follow the chain of events backwards through time, it cannot go back infinitely, so eventually you arrive at the first cause.
- This cause must, itself, be uncaused.
- But nothing can exist without a cause, except for God.
- Therefore, God exists.
The most concise answer to this argument is: "Who created God?", which in turn raises the question "Who created God's creator?", and so on ad infinitum. This is also related to the phrase "It's turtles all the way down".
The typical response to this is that God always existed. This attempt to terminate the infinite regress is flawed as an uncaused god is posited as the beginning, but the notion of the universe being uncaused is automatically denied. If we are to posit that the universe had to have the uncaused god as a beginning for the universe, why not save a step and say "the universe always existed"?.
There is a contradiction between the first statement and the second statement. If "everything that exists has a cause" then there cannot exist anything that does not have a cause, which means that there is no first cause. Either some things can exist without causes, or nothing can. It can't be both ways.
Changing "Everything that exists has a cause" to "Everything that begins to exist has a cause" produces a variant known as the Kalam cosmological argument.
It is also not necessarily the case that there are not an infinite chain of causes and effects. It is widely agreed among scientists that our universe had a beginning (the Big Bang) but we don't know what occurred in the first split second after the big bang, nor can we comment on anything that came before it, as no experiments have yet been devised to test any theories about these early moments. (For further discussion on this topic, see the Big Bang article.)
First law of thermodynamics
This argument can be associated with the First Law of Thermodynamics, which says that the amount of mass and energy in the universe will remain constant. They cannot prove the proposition "everything has a cause" without proving the First Law of Thermodynamics. Since this law only talks about mass and energy, space-time itself can, as far as we know, pop into existence whenever it wants. Some scientists, especially those who favor M-theory, say that, in a multi-universe model, when two universes collide it could create a matter and energy in a big bang, which would be the cause of mass and energy. Therefore, it is entirely possible for the universe to arise from material sources.
Why assume the first cause is god-like?
- See also: Which god?
Even if we grant that a first cause exists, it makes no sense to assume that it is any kind of god, let alone Yahweh. The idea of an intelligent, universe-creating god "just existing" is far more difficult to explain than the universe itself "just existing". Intelligence is one of the most complex things we are aware of in the universe. To assume a being who is so intelligent that it can design an entire universe, as well as micromanage the personal lives of billions of people on earth through prayer, would require an enormous amount of explanation.
Christians try to avoid this issue by saying "God does not need a cause because He is outside of time." This is a glib non-answer. If all that is required to get around the first cause argument is an entity that exists outside of time, then all we need to do is postulate a single particle that exists outside of time and triggered the big bang. It need not have any special powers at all. Besides, this particle might even exist, depending on how you define "outside of time". Photons, light particles, do not experience time, since they move at the speed of light. Therefore, according to this argument, light can pop into existence without cause.
Theists will object that this particle should have a cause. But they have already refuted this argument by granting that there exists an uncaused cause in the first place. If God can exist without a cause, why not a particle? Why not the universe?
An Inductive Cosmological Argument
Richard Swinburne develops an inductive cosmological argument that appeals to the inference to the best explanation. Swinburne distinguishes between two varieties of inductive arguments: those that show that the conclusion is more probable than not (what he terms a correct P-inductive argument) and those that further increase the probability of the conclusion (what he terms a correct C-inductive argument).
Swinburne notes that if only scientific explanations are allowed, the universe would be a brute fact. If the universe is finite, the first moment would be a brute fact because no scientific causal account could be given for it. If the universe is infinite, each state would be a brute fact, for though each state would be explained by the causal conditions found in prior states plus the relevant physical laws, there is no reason why any particular state holds true rather than another, since the laws of physics are compatible with diverse states. That is, although the features F of the universe at time t are explained by F at time t1 plus the relevant physical laws L, and F at t1 is explained by F and L at t2, given an infinite regress there is no reason why F or L at tn might not have been different than they were. Since F and L at tn are brute facts, the same holds for any F explained by F and L at tn. Hence, regardless of whether the universe is infinite or finite, if only scientific evidence is allowed, the existence of the universe and its individual states is merely a brute fact, devoid of explanation.
The universe, however, is complex, whereas God is simple. But if something is to occur that is not explained, it is more likely that what occurs will be simple rather than complex. Hence, though the prior likelihood of neither God nor the universe is particularly high, the prior probability of a simple God exceeds that of a complex universe. Hence, if anything is to occur unexplained, it would be God, not the universe. On the other hand, it is reasonable to appeal to God as an explanation for the existence of a complex universe, since there are good reasons why God would make such a complex universe “as a theater for finite agents to develop and make of it what they will” Consequently, if we are to explain the universe, we must appeal to a personal explanation “in terms of a person who is not part of the universe acting from without. This can be done if we suppose that such a person (God) brings it about at each instant of time, that L operates” . Although for Swinburne this argument does not make the existence of God more probable than not (it is not a P-inductive argument), it does increase the probability of God's existence (is a C-inductive argument) because it provides a more reasonable explanation for the universe than merely attributing it to brute fact.
Swinburne's point is that to find the best explanation, one selects among the possible theories the theory that provides the best explanation. In light of the complexity of the universe, which of the overarching theories of materialism, humanism, or theism provides the best explanation? Swinburne notes four criteria to be used to determine the best explanation: an explanation is justified insofar as it provides predictability, is simple, fits with our background knowledge, and explains the phenomena better than any other theory He suggests that fit with background knowledge does not apply in the case of the cause of the universe, for there are no “neighboring fields of inquiry” where we investigate the cause of the universe. Indeed, he suggests, this criterion reduces to simplicity, which for him is the key to the inductive cosmological argument Appeals to God's intentions and actions, although not leading to specific predictions about what the world will look like, better explain specific phenomena than materialism, which leaves the universe as a brute fact. Swinburne concludes that “Theism does not make [certain phenomena] very probable; but nothing else makes their occurrence in the least probable, and they cry out for explanation. A priori, theism is perhaps very unlikely, but it is far more likely than any rival supposition. Hence our phenomena are substantial evidence for the truth of theism”.
A second reason for Swinburne is that explanation can be reasonably thought to have achieved finality when one gives a personal explanation that appeals to the intentions of a conscious agent. One may attempt to provide a scientific account of why someone has particular intentions, but there is no requirement that such an account be supplied, let alone be possible. We may not achieve any better explanation by trying to explain physically why persons intended to act as they did. However, when we claim that something happened because persons intended it and acted on their intentions, we can achieve a complete explanation of why that thing happened.
Third, appeal to God as an intentional agent leads us to have certain expectations about the universe: that it manifests order, is comprehensible, and favors the existence of beings that can comprehend it. For Swinburne, who in his works often discusses this antecedent probability, this accords with his predictability criterion. Finally, Swinburne introduces a fourth feature, namely, the simplicity of God that, by its very nature, makes further explanation either impossible or makes theism the best explanation. This consideration leads to discussion of God's properties and the nature of simplicity.
Still, Mackie notes, raising the probability of God's existence is not of great assistance, for “the hypothesis of divine creation is very unlikely.” Indeed, it is very unlikely that a God possessing the traditional theistic properties exists. Hence, increasing the probability of something very unlikely initially leaves us with the unlikely. Swinburne's response is that although theism is perhaps very unlikely, it is far more likely than any supposition that things just happen to be. So we return to what constitutes the best explanation of the existence of the universe.
See also An atheistic argument from contingency http://forum.richarddawkins.net/viewtopic.php?f=18&t=105133
 This is a typical understanding of this argument type, see e.g. the Cosmological Argument entry at the Stanford Encyclopedia of Philosophy.