Why does anything exist at all? Or to put it another way "Why is there something rather than nothing?" Or to put it another way still "Why this form of existence as opposed to another?" The three different ways of presenting this question demonstrates the complexity regarding the very notion of existence and the philosophical considerations that accompany it.How can we unpack this question? As part of my Biggest Questions Podcast Series I have been conducting a series of discussions and interviews with the some of the world's leading thinkers on such matters and the complex nuances that encompasses them. What is more notable then perhaps anything else is that this appears to be a directly valid metaphysical question. Many anti metaphysics Philosophers and Scientists deny this assertion but it is hard to arrive at another conclusion and despite the continuous disputes regarding the validity of metaphysical study, the sheer profoundness of the question makes it worthy of addressing in some fashion nonetheless.
Throughout history many a mind have attempted to provide answers to the overall perplexing question of "Why does anything exist at all?" These attempts can be principally captured by the dichotomy of Theism/Atheism. However this only tells half the story because more importantly both of these opposing categories have to deal with two indispensable concepts which are necessity and probability. Moreover it is the problematic relationship of necessity and probability faced by both sides that paves the way for probing the question of "Why does anything exist at all?"
First let's take necessity and what the opposing Theistic and Atheistic positions have said about its relationship to existence. Historically, Theists have argued that this form of existence that we find ourselves in necessarily requires God as the ultimate causal explanation, a position bore out today by the likes of William Lane Craig and Joseph Spitzer. The Theistic argument here attempts to distinguish itself by employing God as the ultimate causal explanation as a means to solving the problem of infinite regression and the problem of "nothing". The problem of infinite causal regression arises out of the principle of sufficient reason because anything that exists must have a cause but then what caused that cause and so on. Certain Theists take the opportunity presented by the problem of actual existing infinites, itself a highly contentious issue, to present an argument that infinite regression is not possible and because the buck must stop somewhere this means that time, space and the Universe where brought into being by something that is itself causeless and timeless but yet still causes all things. This is another version of the prime mover argument and, as some Theists still argue, is the only way to dissolve the potential problem of infinite regression.
God as the ultimate causal explanation also deals with the controversial issue regarding the conceptual definition of "nothing" which itself has a long history of putting the wind up both Philosophers and Scientists. The Atheistic argument deals with necessity whilst addressing the problems of "nothing" and infinite regression like their counter posing Theistic rivals. Why must the universe necessarily exist? The laws of nature are responsible for it. Our Universe is a necessary outcome of some process whether it is quantum fluctuations, multiverses or a yet to be discovered Meta law of Physics. The Atheistic argument mirrors the problems of the Theistic argument, repackaging the problem and hurling them back in the opposite direction. For example how can something come from nothing? Well if God can be causeless and outside time and space then so too can quantum wave fluctuations be outside time and space, be causeless and infinite; and if God causally solves the issue of infinite causal regression God itself cannot escape the conceptualisation of infinity itself.
Whilst the issue of probability adds another dimension to answering the question it also presents new problems in relation to necessity for both sides. God is necessarily existent in itself but our Universe is not, yet because our Universe exists God is necessarily the causal explanation for it. Therefore the Universe is the probable outcome of the agency of God because it satisfied God's ideal criteria of intrinsic good and thus it follows that the existence of our Universe was highly probable because it achieves this intrinsic good. This is an adaptation of the traditional creative story endorsed by Philosophers such as Peter Forrest but take this to its logical conclusion, which is that it is probable that we exist because it fulfills "good" that we exist, then once again our existence becomes necessary. Similar issues in Theoretical Physics strain the boundaries between necessity and probability once more. An example of this is quantum wave fluctuation in which particles come in and out of existence. This means it is highly probable that a universe would come into existence but given the constant presence of wave fluctuations does probability over multiple repetitions mean that a Big Bang is at some point a necessity?
Why the world exists is a viable metaphysical question but answering it means that we must wrestle with our conceptions of necessity and probability when specifically applied to this question. In terms of logical proposition necessity and probability require greater consideration in this area for it is clear that we cannot define one without the other. Furthermore we may need to subsume probability under necessity meaning that whatever position you take in answering the question, whether Atheistic or Theistic, the Universe may have to be a necessity. Attempting to answer this question also makes us question our logic behind temporal linearity, the symmetric nature of causation and the definition of "nothing". Can something really can from nothing? Can an uncaused event cause another event? And can an effect preclude a cause? As for those that believe "Why does anything exist at all?" is a logically unanswerable question in a positive sense they cannot avoid the ironic fact that they are answering it in a negative sense.