Cosmogony, or cosmogeny, is any theory concerning the coming into existence or origin of the universe, or about how reality came to be. The word comes from the Greek κοσμογονία (or κοσμογενία), from κόσμος "cosmos, the world", and the root of γί(γ)νομαι / γέγονα "to be born, come about". In the specialized context of space science and astronomy, the term refers to theories of creation of (and study of) the Solar System.
Cosmogony can be distinguished from cosmology, which studies the universe at large and throughout its existence, and which technically does not inquire directly into the source of its origins. There is some ambiguity between the two terms, for example, the cosmological argument from theology regarding the existence of God is technically an appeal to cosmogonical rather than cosmological ideas. In practice, there is a scientific distinction between cosmological and cosmogonical ideas. Physical cosmology is the science that attempts to explain all observations relevant to the development and characteristics of the universe as a whole. Questions regarding why the universe behaves in such a way have been described by physicists and cosmologists as being extra-scientific, though speculations are made from a variety of perspectives which include extrapolation of scientific theories to untested regimes and philosophical or religious ideas.
Attempts to create a naturalistic cosmogony are subject to two separate limitations. One is based in the philosophy of science and the epistemological constraints of science itself, especially with regards to whether scientific inquiry can ask questions of "why" the universe exists. Another more pragmatic problem is that there is no physical model which can explain the earliest moments of the universe's existence (Planck time) because of a lack of a consistent theory of quantum gravity.
Theistic explanations for origins indicate one or more supernatural beings as the explanation, though atheist commentators often point to this as an argument from ignorance or a God of the gaps fallacy, and that such an assumption provides no explanation for existence of the deity. Nondual explanations by contrast state that the very question is misleading, since it contains erroneous assumptions of beginnings, endings and the nature of existence itself, and consider the visible universe as phenomenology.
As a result of this, scientific cosmogonies are sometimes supplemented by reference to metaphysical and theistic belief systems. The problem can be summarized as three classical paradoxes. These paradoxes (discussed by both Kierkegaard and Leibniz) are:
However, some of the metaphysical principles used to formulate these classical paradoxes no longer enjoy an unchallenged status as laws of thought. For instance, quantum mechanics gives an independent motivation to challenge the principle of sufficient reason.
Planck time (10-43s) is the time it would take a photon travelling at the speed of light to cross a distance equal to the Planck length. It has been proposed that this may be the hypothetical "quantum of time", the smallest measurement of time that has any meaning, although in current physics theory time is not quantized.
Although the laws of physics lose experimental support at the Planck time, modern science has sought to clarify the nature of these paradoxes, so far with only limited success. For example, one can apply the current understanding of grand unified theories (GUTs) both quasi-classical (such as general relativity) and modern (such as quantum gravity, superstring, and M-theories) to these three primary cosmogonic paradoxes in thought experiments. While these result in some contradictions and lack completeness in a mathematical sense (being based on axioms that are 'merely' self-evident, but not robust under the stresses of radical scepticism) these paradoxes can nonetheless be analyzed rationally using the subatomic applications of quantum cosmology, particularly through the employment of the Schrödinger wave equations.
In each case, where general relativity fails as the curvature of space-time invokes singularities from its equations at t=0, the statistically "grey" nature of quantum cosmology tends to allow a scientific rationale to account for each paradox, and in so doing allows for a scientific perspective on previously theistic terrain. For example, application of quantum "fuzziness" (per the Wheeler-DeWitt application of subatomic position and momentum equations to universal radius and expansion) avoids boundary issues, as developed in the Hawking-Hartle Wave Function.
All such equations are based on differentials, which assume a continuum, where in our universe, affected by the Planck length and other minimum scales, this continuum has only limited meaning, about which philosophy remains in a state of semantic flux.