The cosmological argument is an argument for the existence of God. It is also known as the first cause argument for the existence of God, or the prime mover argument. There are three versions of this argument: the argument from causation in esse, the argument from causation in fieri, and the argument from contingency.
1 Origins of the argument
Thomas Aquinas, the most famous philosopher of the Middle Ages, adapted an argument he found in his reading of Aristotle to form one of the earliest and the most influential versions of the cosmological argument. His conception of first cause is the idea that the universe must have been caused by something which was itself uncaused, which he asserted was God.
The phrase "first cause" is sometimes used as an alternative noun for God among individuals uncomfortable with the historical and religious meanings associated with the term. Using "first cause" in replacement of "God" may also indicate that the writer has a different conception of God than what the popular definition entails.
The cosmological argument does not attempt to prove anything about God besides existence. Scholastic philosophers believed, however, that further arguments can be used to prove to anyone via logic some attributes of God, such as his omniscience, simplicity (i.e., total lack of composition), and more. However, they believed other things can not be known about God by deduction and can only be known by divine revelation.
Framed as a formal proof, the first cause argument can be stated as follows:
The cosmological argument infers the existence of God from claims about the entire universe. Fundamentally, the argument is based on the claim that God must exist due to the fact that the universe needs a cause. In other words, the existence of the universe requires an explanation, and an active creation of the universe by a being outside of the universe—generally assumed to be God—is that explanation.
The cosmological argument rests on the assumption that there need be a first cause. This assumption is made because of the conceptual difficulty of imagining an infinite regress. Aquinas' version does not assume that the first cause is an omnipotent, omniscient, and all-benevolent God, but later attempts to prove also that this is true.
In light of the Big Bang theory, a stylized version of the basic cosmological argument (sometimes called the Kalam cosmological argument, most recently defended by William Lane Craig) for the existence of God has emerged:
A more detailed explanation might go something like this:
Consider some event in the universe. Whatever event you choose, it will be the result of some cause, or more likely a very complex set of causes. Of course each of those causes would be events, which were the result of some other set of causes. Thus, there is an enormous chain of events in the universe, with the earlier events causing the later events. Now, either this chain of events has a beginning, or it does not.
Currently, the theory of the cosmological history of the universe most widely accepted by astronomers arguably includes an apparent first event—the Big Bang—the immense explosion of all known matter and energy from a superdense point at some finite time in the past. If this really is the first event in the universe, this explosion could not be the result of any prior event. According to the cosmological argument, the cause of the first event would necessarily be a being which is capable of causing other events, but which is not itself caused. Aristotle called this the Uncaused Cause, and left it at that, but Aquinas went on to argue that this Uncaused Cause is just another name for God.
Though contemporary versions of the cosmological argument assume that there was a beginning to this chain of causes, Aquinas' formulation did not make such an assumption, due to his view that it was impossible to prove that the universe did have a beginning.
According to Aquinas, it is logically possible that the universe has already existed for an infinite amount of time, and will continue to exist for an infinite amount of time. Even if the universe has always existed, (a notion which Aquinas rejected on other grounds) there is still a question as to why this infinite chain of causes exists.
Aquinas follows Aristotle in claiming that there must be something which explains why the universe exists. Since the universe could exist or not exist, that is to say it is contingent, its existence must have a cause. And that cause cannot simply be another contingent thing, it must be something which exists by necessity, that is, it must be something which must exist. In other words, even if the universe has always existed, it still owes that existence to Aristotle's Uncaused Cause.
So Aquinas comes to the same conclusion, that God exists, whether there was a first event in the universe or not. Since either the universe has always existed, or it had a first event, Aquinas says that this argument definitively proves the existence of God.
The German philosopher Gottfried Leibniz made the same point with his Principle of Sufficient Reason in 1714. He wrote: "There can be found no fact that is true or existent, or any true proposition, without there being a sufficient reason for its being so and not otherwise, although we cannot know these reasons in most cases." He formulated the cosmological argument succinctly: "Why is there something rather than nothing? The sufficient reason...is found in a substance which...is a necessary Being bearing the reason for its existence within itself."
The cosmological argument depends on several assumptions. Most objections center on two of them:
The cosmological argument attempts to prove that a First Cause exists, but does not even attempt to ascribe this First Cause with attributes necessary to call it "God," not even with extremely basic prerequisites such as self-awareness and will. It simply names the First Cause as "God" without proving that it has the characteristics that that name implies. Furthermore, the argument only requires God as a first cause, but fails to prove that God continued to exist after serving that purpose. Some deists agree that the argument proves that God created the universe, but nevertheless God then in most traditionally conceptualized sense ceased to interact with the material universe.
Opponents point out that the cosmological argument applies temporal concepts to situations where time does not exist. For example, "cause" is a temporal concept - by definition, it requires time; things which exist outside of time do not have to be caused. (Indeed, this is the excuse given for God's unrequirement to be caused.) However, time is merely a property of the universe, and so the laws of time (ie. cause) cannot be logically applied to the universe itself as a whole. Similarly, time can begin, but not require a cause, since all human concepts of a caused beginning have something before that beginning (including the cause); this is not true of time itself.
An assumption in some cosmological arguments (e.g., the Kalam argument, but not Aquinas' arguments) is that there has to be a "First Cause", ie. that our universe has not "always" existed. This is still an open question, although the standard Big Bang cosmology is consistent with it. Defenders of cosmological arguments that do not assume the finite age of the universe insist that eternal existence, the "always there" assumption, does not eliminate the problem of origin. On a similar note, one could also claim that the universe has always existed and its "creation" is thus not causal in nature, so no "first cause" is necessary. If one believes that time is infinite, then indeed there is no need for a "first cause" and therefore no need for God. However, this view is not compatible with the current scientific understanding of the origins of the universe.
Gottfried Leibniz stated the problem in his conclusion, although his terminology included some assumptions. If his Principle of Sufficient Reason is indeed universally applicable, then the First Thing must either (1) be its own cause or (2) have a non-causal explanation. The non-causal explanation would either (a) make the First Thing's existence be in some way self-explanatory or (b) make it follow in an explanatory way from self-explanatory truths, such as the truths of logic.
All three options have had defenders. Thus, option (1), the causa sui option, is defended by Descartes, despite the obvious criticism that something that is its own cause must have its existence be prior (in the order of explanation, not necessarily that of time). Option (2a) is held by some of those like Aquinas who think that God's essence is identical with God's existence, or by those who hold, more weakly, that God's existence follows from his essence. Option (2b) essentially holds that there is a sound ontological argument for the existence of God, albeit we may not have discovered it yet. It follows from the Principle of Sufficient Reason that one of the three options holds, but a defender of the Principle does not need to give an independent proof of any one of these options. It is, after all, the conclusion of the argument that one of these holds. In fact, this conclusion might be the starting point for responding to the problem of identifying the First Thing with God--that is how it is in Aquinas, for instance. Thus, if one could show the premises of the cosmological argument to be true and show that options (1) and (2a) were not tenable, then the cosmological argument would turn into an argument for the existence of an ontological argument. We would then know that there is a sound ontological argument, even if we did not know what it is.
Alternately, the defender of the cosmological argument can restrict the Principle of Sufficient Reason in such a way that it does not require us to give an explanation of the existence of the First Thing. One such restriction would be to restrict the Principle only to require the explanation of contingent facts. Another is to restrict the Principle only to require the explanation of explainable facts. These restrictions would require arguments, respectively, that the universe is contingent or that the universe's existence is explicable.
If the Principle of Sufficient Reason does not hold, then the "selection" among potential alternatives must be random or a "brute fact". Defenders of the Principle will insist that neither option really makes sense.
An early argument for the finite age of universe (and hence the first cause) was based on the second law of thermodynamics and growth of entropy. Entropy tends to grow in an isolated system, and the Universe can be considered as an isolated system with finite amount of matter and particles. If the Universe was infinitely old, the entropy had already gained its maximum extent, there would be no differences in temperature and the universe would itself have suffered the heat death already. Time itself can in this model be understood as the gradient of entropy. Since the heat death has not yet occurred, the age of the universe is finite and it has not existed eternally. This argument is not fool-proof, however, as there are stochastic processes associated with many physical theories that can reset the entropy clock through, for example, cosmic inflation.
Modern quantum physics is sometimes interpreted to deny the validity of the first premise of this argument (that everything has a cause), showing that subatomic particles such as electrons, positrons, and photons, can come into existence, and perish, by virtue of spontaneous energy fluctuations in a vacuum. Such occurrences do not violate the Law of Conservation of Mass and Energy, and they are not essentially different from other natural stochastic processes which are not presently fully understood (with some saying that it is impossible to predict them, and others saying otherwise, eg Albert Einstein: "He does not throw dice". However, the quantum vacuum from which the subatomic particles arise from is not literal nothingness but a sea of fluctuating vacuum energy. Thus, it is not presently known whether such processes have any bearing on the assertion that all effects have causes.
Modern cosmology is sometimes taken to be neutral on the second premise, asserting that while spacetime as observed tends toward a singularity giving the universe an observed finite age, this does not discount the possibility that the stochastic processes that govern the early evolution of the universe actually cause the universe to be eternal. In particular, the lack of a consistent theory of quantum gravity has meant that there is no physical theory and no meaningful prediction can be made about what character the universe had before the Planck time. Indeed the supposed singularity from which the universe is said to have originated in the classic Big Bang picture is actually a physical paradox - an indication that current theory is not an adequate description. This era of the universe and its associated energy regime remains one of the unsolved problems in physics and as such does not lend itself either to the existence of a "first cause" or lack thereof.
Recently, newer, speculative theories have been offered by a number of theorists, but there is no scientific consensus as of yet on whether the universe necessarily began to exist or whether it is eternal.