The argument from first cause (or the cosmological argument) states that the universe must have a cause, and that this cause is God.
 Argument structure
The argument from first cause proceeds as follows.
 Everything that comes into being must have a cause
This is determined from both observation and the logic behind causality. Everything that is observed in the universe has some form of cause behind it and this forms the basis of conservation of momentum and energy. Within causality there is a unifying logic between an effect (something caused) and an affect (cause). An affectless effect and an effectless affect are logically nonsensical propositions.
 An infinite regress of causes is impossible.
Disallowing an infinite regress of causes is, technically speaking, an assertion required for the argument to work. However, a form of pleading can be made that while an infinite regress of temporal causes may be allowable, an infinite regress of non-temporal causes may not. In other words, a sequence of events in time may be able to go infinitely forward through the future and back through the past but time itself must have some other form of cause.
 We must therefore arrive at a first cause.
Following from disallowing an infinite regress of causes, there must be a point where the first cause appears. This is the concept first developed by Aristotle and expanded upon by Aquinas as the "unmoved mover" or the "uncaused causer".
 This first cause is God.
Having established the existence of the first cause, it is asserted that this cause is none other than the God of choice of the person making the argument.
 Kalām version
- Everything that exists/begins to exist has a cause of its existence.[note 1]
- The universe exists/began to exist.
- Therefore, the universe has a cause of its existence.[note 2]
 Platonic / Aristotelian version
- Every finite and contingent being has a cause.
- A causal loop cannot exist.
- A causal chain cannot be of infinite length.
- Therefore, a First Cause (or something that is not an effect) must exist.
 Thomistic version
- A contingent being exists.
- This contingent being has a cause of its existence.
- The cause of its existence is something other than itself.
- What causes this contingent being to exist must be a set that contains either only contingent beings or a set that contains at least one noncontingent (necessary) being.
- A set that contains only contingent beings cannot cause this contingent being to exist.
- Therefore, what causes this contingent being must be a set that contains at least one necessary being.
- Therefore, a necessary being exists.
 The assumptions
 Self-causation is impossible
Related to the infinite regress of causes is the idea that something may cause itself to come into being. Aquinas argues that this is impossible on account of it never having been empirically observed, but also because of the impossibility and absurdity of an object causing itself. Specifically, for an object to cause itself to come into being, it must be prior to itself. This expressly forbids the universe from causing itself, which would otherwise scupper the conclusion.
The reasoning does not seem to apply to the laws of physics, since the notion of "being prior", e.g. preceding something in time, requires time to already exist to have any meaning.
 Prohibition of infinite regress
The argument assumes that an infinite causal chain cannot occur. While at the time the argument was first proposed this assumption was entirely unsupported, since an eternal universe might contain causal chains of infinite length, today we know that the universe did have a beginning. Therefore this assumption may be regarded as sound when referring to our universe. Nevertheless, in the standard cosmological model, inflation makes it debatable whether the multiverse had a beginning or not.
 Uniqueness and identity of the first cause
As Aquinas said at the end of his first cause argument:
“”Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.
There are two rather big assumptions in this sentence: first, that by following a causal chain back in time, one will eventually always arrive at the same starting point; and second, that this causal starting point is in fact a very specific God – precisely the one the arguer has in mind. The first assumption is wrong if, for example, each of the four fundamental forces of nature (strong nuclear force, weak nuclear force, electromagnetism and gravity) was created by a different god. The second has no basis at all, and constitutes a bit of sleight of hand.
A commonly-raised objection to this argument is that it suffers from special pleading. While everything in the universe is assumed to have a cause, God is free from this requirement. However, while some phrasings of the argument may state that "everything has a cause" as one of the premises (thus contradicting the conclusion of the existence of an uncaused cause), there are also many versions that explicitly or implicitly allow for non-beginning or necessary entities not to have a cause. In the end, the point of the premises is to suggest that reality is a causally-connected whole and that all causal chains originate from a single point, posited to be God. That many people using this argument would consider God exempt from various requirements is a foregone conclusion, but citing "special pleading" because finite causal chains are said to have an uncaused beginning is hardly a convincing objection.
A more pertinent objection is that, even assuming that there is a first cause, the argument utterly fails to address how we can know its identity. The assertion that it must be the particular God that the arguer has in mind is a complete non sequitur. Why not the deist God? Why not some kind of impersonal, eternal cosmic force? Why not shape-shifting aliens from another dimension? Or maybe the most simplest of all, why not the Big Bang as the first cause? There is nothing in the argument that would allow one to determine any attributes of the first cause.
Finally, there is nothing in the argument to rule out the existence of multiple first causes. This can be seen by realizing that for any directed acyclic graph[wp] which represents causation in a set of events or entities, the first cause is any vertex that has zero incoming edges. This means that the argument can just as well be used to argue for polytheism.
Through modern science, specifically physics, natural phenomena have been discovered that do not have discernible causes. The best known example is radioactive decay. Although decay follows statistical laws and it's possible to predict the amount of a radioactive substance that will decay over a period of time, it is absolutely impossible to predict when a specific atom will disintegrate. The spontaneous disintegration of radioactive nuclei is truly random and uncaused, providing a counterexample to the assumption that everything must have a cause.
Another example is the spontaneous generation of virtual particles, which randomly appear even in complete vacuum. These particles are responsible for the Casimir effect[wp] and Hawking radiation.[wp] The release of such radiation comes in the form of gamma rays, which we now know from experiment are simply a very energetic form of light at the extreme end of the electromagnetic spectrum. Consequently, as long as there has been vacuum, there has been light, even if it's not the light that our eyes are equipped to see. What this means is that long before God is ever purported to have said "Let there be light!", the universe was already filled with light, and God is rendered quite the Johnny-come-lately.
 See also
- Argument from beauty
- Argument from design
- Argument from fine tuning
- Argument from morality
- Ontological argument
- Cosmological argument, Wikipedia
- Cosmological argument, Iron Chariots
- Cosmological Argument, Stanford Encyclopedia of Philosophy
- Cosmological Arguments, Internet Infidels
- ↑ The change in phrasing from "everything that exists" to "everything that begins to exist" is an attempt to avoid infinite regress and the question of "So what was the cause for (your) god's existence?" in a slightly more clever way than claiming that the deity is self- or uncaused. By referring to "everything that begins to exist", the apologist is pre-emptively excluding any eternal (or "timeless" in William Lane Craig's even more clunky terminology) phenomena or beings (e.g the Abrahamic God).
- ↑ Then add some (more) dubious logic to get from "a cause" to "(my) god". This approach is probably best known from William Lane Craig who has used a version of the Kalām as the cornerstone of his apologetics since at least his 1979 Ph.D. thesis on Philosophy of Religion.