The first and most basic fact about our world is that it exists. The famous contemporary philosopher Derek Parfit writes, “It might have been true that nothing ever existed: no minds, no atoms, no space. When we imagine this possibility, it can seem astonishing that anything exists. Why is there a universe?”
Imagine I showed you a fork, and you asked me where it came from. What if I responded, “Nowhere; it has just always existed.” I doubt you would say, “That’s really cool,” and then move on. Wouldn’t you want an explanation as to why it had existed for so long? Why does it exist at all? Why is it a fork and not a spoon?
Even if the universe were eternal, we would ask the same questions. Why hasn’t the universe ever stopped existing? Why has there been an eternal universe instead of just an eternal state of nothing? The eighteenth-century philosopher G.W. Leibniz proposed an argument for the existence of God that answers the fundamental question “Why is there something rather than nothing?”
Unlike other cosmological arguments (like the kalam), this argument does not rely on proving the universe began to exist and so God brought the universe into being. In fact, it is a benefit of this less famous argument for the existence of God that it doesn’t get sidetracked into issues about whether the past is infinite. Instead, the discussion can focus on the universe as we observe it now and notice that because this current universe could fail to exist (or is “contingent”), it must have an explanation that can never fail to exist (or is “necessary”).
Indeed, Leibniz’s cosmological argument is known as the “contingency argument for God’s existence.”
To be contingent means that something doesn’t have to exist; it could be different, or it could not be at all. Contingent things need other things in order to stay in existence. For example, humans need the oxygen that plants create, the oxygen we breathe needs an atmosphere, the atmosphere requires the planet’s gravity in order to stay together, and so on. We know that humans are contingent because we can imagine a world without them. We can do the same for other contingent objects, such as stars and planets.
In contrast, something is necessary when it is not contingent and so could not be different. The three sides of a triangle are necessary because it is impossible to draw a triangle with more or fewer sides. This fact can’t be different, so we say a triangle’s three sides are necessary to a triangle. The contingency argument claims that the universe’s existence is dependent on something that is not dependent upon anything else in order to exist. Its existence depends on a “necessary” being, such as God. One way to summarize this argument is to say:
The universe either has no explanation, explains itself, or is explained by God. If the universe has an explanation and cannot explain itself, it follows that God explains why the universe exists.
Could the universe simply have no explanation? This seems to violate what philosophers call the principle of sufficient reason. Consider the maxim espoused by the fictional detective Sherlock Holmes: “When you eliminate the impossible, whatever remains, however improbable, must be the truth.” This statement assumes that once the impossible is eliminated, we can’t just say that there is no explanation at all. Instead, the process of elimination forces us to accept even an unlikely explanation, because everything that exists must have an explanation.
Could the universe explain its own existence apart from a necessary being like God? But how could it be the case that the universe must exist? A triangle’s three sides are necessary, and so I can’t imagine a triangle without them; but it’s hard to think the universe’s existence is necessary, because I can imagine it not existing. Everything we know about the universe, including the birth and death of stars and planets, points toward our universe being a collection of things that don’t have to exist.
Now, a critic could retort that if he can imagine a universe without God, then doesn’t that mean God’s existence is not necessary either? The problem with this response is that not everything we can imagine is actually possible. I can imagine the unproven Goldbach’s conjecture (all even numbers greater than two are the sum of two prime numbers) could either be true or false. Because the conjecture is a mathematical truth it is either necessarily true or necessarily false — any imagining to the contrary won’t change this fact. I could imagine either scenario but only one is really possible.
The term “God” just refers to that which must exist in a perfect and unlimited way. Necessary existence is a part of God’s definition (though this fact, on its own, doesn’t prove God exists), so asking why God exists is like asking why fire is warm. Fire is warm because it’s a part of the fire’s nature, whereas asking why a stone is warm makes sense because stones don’t have to be warm. Likewise, it makes sense to ask why anything in the universe, or even the universe itself, exists but not why God exists if he does exist because God just is “being” or “existence” itself.
Now, a critic could argue that the fundamental matter that makes up the universe exists necessarily and so, regardless of whether or not it forms stars and planets, we would still have a universe of fundamental particles that have to exist and just get rearranged over time. The smallest particles we are aware of are called quarks (they’re even smaller than protons, electrons, and neutrons). In order for the universe to be necessary, it would have to be true that it is impossible for these quarks to not exist. It also has to be impossible for these particular quarks to not exist in order to say they are necessary. But couldn’t we have a universe with different fundamental matter? If we could, then the matter that exists can’t be necessary since it could be different. Its contingent nature would still require an explanation in something else.
Even some atheists are unwilling to accept the hypothesis that the universe is necessary and explains itself. Cosmologist Sean Carroll says that, for most scientists, “the search for ultimate explanations eventually terminates in some final theory of the world, along with the phrase ‘and that’s just how it is.’” Notice that Carroll says the likely explanation for the universe is not “and that’s the way it has to be” (a necessary explanation in itself). It’s just a brute fact with no further explanation.
But if we accept the principle of sufficient reason, and we deny the universe explains its own existence, then there must be an explanation of the universe that is not the universe itself. This explanation can’t just be another similar universe or multiverse because this would create an infinite regress of explanations, which can’t explain anything (sort of like an infinite train of boxcars that can’t move an inch without a locomotive). But does this explanation have to be God?
At this point the only candidates left that could explain the universe are necessary ones that must exist. Most philosophers agree that if abstract objects like numbers exist, then they would exist as a result of their own nature. But unlike God, who is a mind with intentions and an ability to exercise those intentions, abstract objects like numbers have no intentions and cannot cause anything to happen in the material world. Therefore, God is the only candidate for a causal explanation of the contingent world that is itself necessarily in existence.
Of course, there is more that could be (and has been said) on this and other arguments for the existence of God. For more on this topic check out my book Answering Atheism, published by Catholic Answers Press.