Many estimates have been made of the number of extra-terrestrial civilizations using approaches such as the Drake equation. These estimates vary considerably according to the many assumptions made, and range from millions to zero (for example, Drake and Sobel 1992; Wilson 2001; Forgan 2009; Frank and Sullivan 2016; Sandberg et al. 2018). Considerations include whether the estimates apply to the Milky Way or the observable universe, include past and future civilizations, and whether communication constraints such as the speed of light are considered. The likelihood of the evolution of advanced Kardashev civilizations or entities should be higher if the entire universe rather than just the observable universe is included. Estimates of the size of the entire universe relative to the observable universe are also uncertain ranging from around 251 times greater (Vardanyan et al. 2011) to very many orders of magnitude greater (Guth 1998). Other things being equal, the likelihood of emergence of an advanced entity should be greater in a large than a small universe.
This reasoning can be extended to the emergence of advanced entities in a multiverse consisting of many individual universes. Multiverse theories include the idea that our universe is infinite with every possibility realised in some part of it, eternal inflation with an infinite number of pocket universes, and the many worlds interpretation of quantum mechanics (see Tegmark 2003; Page 2008).
The multiverse is a substantial area for investigation and analysis in theology and philosophy as well as physics. The possibility that God may or may not have created the multiverse has been discussed (Page 2008; Chan 2015), as has the relevance of the multiverse to the problem of evil (Megill 2011; Kraay 2013; Ignatova 2019; Rogers 2020). Multiverse ideas have also been used in discussion of the nature or existence of God involving model realism and possible worlds (Kraay 2010), and in proofs of the existence of God (Spitzer 2019).
The likelihood of an advanced entity capable of creating and controlling new universes arising in an infinitely large multiverse (including an infinitely large universe) should be greater than in a single universe of finite size. In this context, appeal can also be made to the plenitude principle that no genuine potentiality of being can remain unfulfilled (Lovejoy 1976; Kane 1976; Kragh 2019). It could thus be inevitable that such an entity will evolve somewhere at some time in an eternal existence of a potentially infinite number of universes, even if the probability of any given universe generating advanced entities is small.