In recent years, a way of arguing for God’s existence has been receiving new attention. It is known as the Kalam cosmological argument, and it can be put simply:
- Everything that has a beginning has a cause.
- The universe has a beginning.
- Therefore, the universe has a cause (i.e., God).
The Kalam argument has its roots in Christian and Jewish thought, but it received its name because of its popularity in the Muslim world. The Arabic word Kalam originally meant “word” or “speech,” but it became the name of a theological tradition that was the Muslim equivalent of scholastic theology. The Kalam argument thus got its name because it was popular with medieval Muslim scholastic theologians.
Contact with Muslim thought in the thirteenth century led Christian thinkers to debate the merits of this argument. Some such as St. Bonaventure (1221-1274) favored it, while others such as St. Thomas Aquinas (1225-1274) did not.
Most Catholic thinkers found Aquinas’s position more convincing, and the Kalam argument did not receive much discussion until the past few years, when Protestant apologist William Lane Craig began to popularize it.
After he began writing and speaking about it, other apologists picked it up, and it’s easy to see why: it is much simpler to present and make intelligible to ordinary people than other arguments for God’s existence. Also, with the discovery of the Big Bang, modern science seemed to support its premise that the universe had a beginning, making it persuasive for people impressed with modern science.
Today, many Catholics are enthusiastic supporters of the Kalam argument, but the fact that it went into eclipse for so long in Christian thought should give us pause. No matter how easy it is to present, we should ask ourselves whether our intellectual forebears who set it aside may have had good reason to do so.
If someone as brilliant as Aquinas found it unconvincing, we should take that seriously and examine the argument to see how much enthusiasm for it is actually warranted.
Some cautions
When I first discovered the Kalam argument several decades ago, I was an enthusiastic supporter, though I recognized that not all of the arguments people were using to support it actually worked.
With the passage of time, I’ve become more convinced of the argument’s limitations, and while I wouldn’t tell someone not to use the argument, I would warn him to be cautious in how he presents it.
In principle, the argument works. It’s true that everything with a beginning has a cause and that the universe had a beginning. From those facts, you can infer the existence of God as the cause of the universe. But just because an argument is logical doesn’t mean it will be convincing to a nonbeliever.
Of course, when presenting it to someone, you often have to deal with certain misunderstandings. The most common is an objection that portrays the argument as proving too much: “If everything has to have a cause, then God would need one too!”
This misreads the argument. The claim isn’t that everything requires a cause; it’s that everything with a beginning has a cause. Since God doesn’t have a beginning, he doesn’t need a cause.
Even once misunderstandings such as this are cleared away, the skeptic can object to either of the argument’s premises. Some may object to the first premise—that everything with a beginning has a cause—but this is well supported by both intuition and experience. Alternately, the skeptic may object to the second premise—that the universe had a beginning—and this is where the real difficulties come in.
A finite history
Scripture and Tradition reveal that the universe hasn’t always existed, but the skeptic isn’t going to accept Scripture and Tradition. You’ll need to prove to him that the universe has a beginning from reason alone, and this is harder to do than you might think.
To support the idea that the universe has a finite history, Kalam advocates commonly appeal to two forms of evidence: scientific and philosophical.
The scientific appeal is straightforward. The claim is that modern Big Bang cosmology supports the idea that the universe began approximately 13.7 billion years ago, when all the matter in the universe was compressed into a tiny point with infinite density. This then blew apart and eventually gave rise to all the galaxies, stars, and planets.
Before the Big Bang, there was no space and no time, meaning that the universe came into existence out of nothing, implying both a creator as the cause of the universe and specifically a creator who is outside of space and time.
The philosophical arguments are similarly straightforward: For one reason or another, logic precludes the idea of the universe having an infinite history, and so it must have had a beginning.
But there are difficulties with both of the scientific and philosophical arguments.
Science is provisional
Scientists point out that all of their findings are provisional. They are inferences based on data gathered from observing the world, and since we can’t observe everything in the cosmos across all its vastness in space and time, the data is always partial.
That means we have to extrapolate. We have to base our scientific ideas about the world on the assumption that the data we have is representative of the data we would have if we could observe everything in the history of the cosmos.
But that might not be true. Our present observations might not be representative of the universe as a whole. Things might be different in other times and places. Or we may have been missing things even in the part of the universe we can see.
Consequently, we might get new data in the future that contradicts our present theories, in which case they’d need to be revised. Thus, all the findings of science are provisional and subject to change.
This means we need to be cautious when basing arguments on science. It’s not that this shouldn’t be done, but it has to be done with great caution, because scientific theories change with time. Science is even subject to fashions, and theories that are in fashion in one decade may be out of fashion in just a few years, so you can’t appeal to popular ideas as if they were certainties.
The shift in cosmology
The last few years have seen a notable shift in how scientists understand Big Bang cosmology.
At one time, it was commonly proposed that space and time came into existence with the Big Bang, when all matter and energy was compressed into an arbitrarily or infinitely dense point. You’ll still find that language in some popular science writings, but new findings in the past thirty years have led many scientists to reject this picture.
They still believe in the Big Bang, of which we have good evidence. However, that’s all that can be confidently said from a scientific perspective. It is not considered settled science that there was an infinitely dense singularity or that space and time came into existence at this point.
Many scientists argue this was not the case, because if it had been, it would let us make predictions about the universe that are contradicted by observation. For example, if there had been an infinitely hot, dense point, it would lead to large temperature fluctuations in the cosmic microwave background radiation, the Big Bang’s afterglow. But the fluctuations we find are 30,000 times smaller than the ones needed for that scenario.
Other scientific arguments have been proposed supporting a finite past. For example, a trio of scientists have proposed a theorem (the eponymous Borden-Guth-Vilenken theorem) that implies any universe that expands must have a beginning.
However, this theorem is based on assumptions that are not universally granted among physicists. If you change the assumptions, the theorem’s conclusion doesn’t hold.
The fact is that there are numerous competing models for what happened before the rapid expansion that occurred 13.7 billion years ago, and scientists don’t agree about which—if any—the evidence best supports.
This means an apologist must be cautious in how he makes his case. Unless he is an expert in astrophysics, he can’t build a case from the ground up and must rely on expert opinion. But with the experts divided, he can’t present a given scenario as one on which the scientific community agrees.
Philosophical arguments
There are also problems with the philosophical arguments used to support the idea that the universe must have a finite past.
Make no mistake: critics of the Kalam argument such as Aquinas hold that the universe did have a beginning. But they hold that this is something we know by divine revelation, not something that reason alone can prove.
To prove it by reason, you would need to show that an omnipotent God could not create a universe with an infinite history. However, by virtue of his omnipotence, God is able to create anything that is logically possible.
In other words, he can create anything that does not involve a contradiction in the terms used to express it. God can’t make married bachelors or four-sided triangles because these concepts contain logical contradictions, but he can make anything he chooses that doesn’t involve a contradiction.
The burden of proof thus falls to the philosophical defender of the Kalam argument to show that the concept “universe with an infinite history” involves a logical contradiction. Otherwise, God will have the power to create one.
Traversing an actual infinite
One of the most common arguments is that the universe can’t have an infinite history because you cannot traverse an actually infinite series of moments.
This would be like starting with the number 0 and counting 1, 2, 3, etc. No matter how high you count, the result will always be a finite number. Eventually, you’ll hit numbers such as a billion, a trillion, and a centillion, but you’ll never be able to count up to infinity by adding a new number.
In the same way, you could not start at negative infinity and count your way toward 0, ending with -3, -2, -1, 0. No matter how far backward from zero you start, it will always be a finite number of moves backward.
All of this is true, but—Aquinas would say—it misses the point (cf. Summa Contra Gentiles, 2:38 ad 3). To see why, we need to keep in mind what the concept of infinity means. Based on the Latin roots in (“not”) and finis (“end”), it means something that is unending or unlimited.
So, what does it mean for a sequence—whether of numbers or of historical moments—to be unlimited? It could mean one of three things:
- The series has a limit at the beginning of the sequence but has no end (such as the sequence of numbers 0, 1, 2, 3 . . . )
- It has no beginning but does have a limit at the end (like the sequence of numbers . . . -3, -2, -1, 0)
- It has neither a beginning nor an end and is thus unlimited in both directions (like the sequence of numbers . . . -3, -2, -1, 0, 1, 2, 3 . . . )
Option 2 is relevant to the idea of a universe with an infinite past, and notice what it would imply: for a sequence of historical moments to be infinite and yet end in the present, that sequence would have to have no beginning.
This is the problem with the argument that you can’t “traverse” an actually infinite series of moments. The idea of traversing something presupposes that you begin somewhere, cross a space, and finish at another place. In other words, you’re moving between two limits—a beginning and an end. And if you’re moving between two limits, then what you’re doing is, by definition, a limited or finite process. This argument also commits the logical fallacy of begging the question (see sidebar).
No actual infinities?
Another common philosophical argument used to defend the Kalam argument goes further. Instead of arguing that you couldn’t traverse an actually infinite series, it holds that actual infinities can’t even exist.
When this claim is made, the question immediately arises, “What about God? Isn’t he infinite?” To which the answer will be given, “Yes, but in a different sense,” and the one making the claim will try to formulate a distinction that allows God not to have limits but imposes limits on all created things.
Thus, it is claimed, God could not create an infinite collection of apples, and so he could not create an unlimited series of moments in the history of the universe.
Personally, I have always been skeptical of the idea that actual infinities cannot exist. In fact, it seems that some do.
For example, God knows an actually infinite number of mathematical facts. He knows that 1+1=2, that 1+2=3, that 1+3=4, and so on. This means that an actually infinite number of mathematical facts exists. However, because mathematics and logic are rooted in God’s nature, one could argue that these facts fall under the exception that allows God to be infinite but created infinities still can’t exist.
But it seems that some do. This follows from two facts: (1) we have unending life and will never cease to exist, and (2) God is outside of time.
From our perspective, the fact we have unending life appears as what’s called a potential infinity. It’s now 2020. Next year will be 2021. And no matter how many years we count into the future—even a billion years from now—it will still be a finite number. We don’t arrive at an actual year called “A.D. Infinity,” making this series only a potential infinity.
But now consider this from the perspective of God. He is outside of time and thus does not change, so he sees all of history all at once. This means he sees all of the unlimited years of our future lives, and that makes it an actual infinity from his perspective.
Sometimes this is challenged, and the claim is made that only the present exists, so the future is not real. What is real—currently—is the year 2020. The year 2021 doesn’t yet exist.
But this view of time would introduce change into God. Specifically, it would introduce change into his knowledge.
Consider how this would work: right now, in eternity, God would know “In time, the year is now 2020.” But then at a later point, God would know “In time, the year is now 2021.”
The only way for that to happen is for God’s knowledge to change. At one moment he knows one thing to be true, and at another moment he knows a different thing is true. The idea that only the present is real thus forces God’s knowledge to change, introducing change into God and pulling him out of eternity and into time.
The only way to honor Christian teaching that God is outside of time and yet changelessly knows the truth about the future is if the future is actually real. That means that, from God’s perspective, all of our endless future years are real, and so an actual infinity of historical moments exists.
But if an infinite sequence of years can exist in the future, so can an infinite sequence of years in the past. If God can create one, he can create the other. And so, if he chose, God could have given the universe an infinite past, just as he gives it an infinite future.
Other arguments—both scientific and philosophical—have been proposed for the idea that the universe has a beginning, but these are some of the most common and the easiest to understand.
From what we’ve seen, there are good reasons we should be cautious about the Kalam argument.
That’s not to say it can’t be used. While the Church teaches that God’s existence can be proved by natural reason, it doesn’t have an official teaching on which particular arguments are to be used.
Both St. Bonaventure and St. Thomas Aquinas are doctors of the Church, so smart and orthodox thinkers have been on both sides when it comes to the Kalam argument, and there is room for diversity of opinion here.
It’s understandable that many today would be enthusiastic about the argument, given its simplicity and the discovery of Big Bang cosmology.
But there are reasons why the Kalam argument has not been popular in the history of Catholic thought, and there are reasons to be cautious today.
It is possible to say that modern Big Bang cosmology is consistent with and suggestive of a universe that has a beginning, but we can’t claim that this has been definitively proved, even in the provisional way that science can prove anything.
Further, the philosophical arguments used to support it are problematic, and they appear to be inconsistent with things the Church teaches about God and man, including God’s changeless omniscience and the reality of our eternal life.
However, the Kalam argument still works in principle. It’s true that everything with a beginning needs a cause. It’s true that the universe had a beginning. And it’s true that God is the cause of that beginning. The problem is making the argument work using reason alone.
Sidebar: Begging the Question
The traversing-an-actual-infinite argument commits the logical fallacy of begging the question because it presupposes that the sequence has both a beginning limit (where you start traversing history) and an ending limit (where you stop traversing in the present), and any sequence like that is guaranteed to be finite.
By contrast, a universe with an infinite history would have no beginning at all—not even one “infinitely far back.” It simply would have always existed. Time would have been progressing toward the present, but if its history is really infinite, there simply was no beginning from which to start counting forward.
The traversing-an-actual-infinity argument thus ends up attacking a straw man: it misunderstands what a universe with an infinite history would involve, and—by presupposing both a beginning and an end—it envisions a finite history instead.