No, the “Kalam cosmological argument” doesn’t prove God’s existence

We know that everything in the Universe, as it exists today, arose from some pre-existing state that was different from how it is at present. Billions of years ago, there were no humans and no planet Earth, as our Solar System, along with the ingredients necessary for life, first needed to form. The atoms and molecules essential to Earth also needed a cosmic origin: from the lives and deaths of stars, stellar corpses, and their constituent particles. The very stars themselves needed to form from the primeval atoms left over from the Big Bang. At every step, as we trace our cosmic history back farther and farther, we find that everything that exists or existed had a cause, and a precursor state, that brought about its existence. Even our Big Bang itself was caused by cosmic inflation, which we presume (but have not proven) must have had an initial cause, itself.

Can we apply this logical structure to the Universe itself? Since the late 1970s, philosophers and religious scholars — along with a few scientists who also dabble in those arenas — have asserted that we can. Known as the Kalam cosmological argument, it can be broken down into three simple steps:

• whatever begins to exist has a cause that brings it into existence,
• and the Universe, which exists, must have began to exist at some point,
• and therefore the Universe itself must have a cause to its existence.

So what, then, is the cause of the Universe’s existence? The answer, according to adherent and defenders of the Kalam argument, must be God. That’s the crux of the argument being made when people assert that “modern cosmology proves the existence of God.” But how well do the premises hold up to scientific scrutiny? Has science proved them, or are other options possible, or even more likely? The answer lies neither in logic nor in theological philosophy, but in our actual scientific knowledge of the Universe itself.

By creating two entangled photons from a pre-existing system and separating them by great distances, we can “teleport” information about the state of one by measuring the state of the other, even from extraordinarily different locations. Interpretations of quantum physics that demand both locality and realism cannot account for a myriad of observations, but multiple interpretations all appear to be equally good.

Let’s start with the very first premise of the Kalam cosmological argument: the assertion that everything that comes into existence, or that begins to exist, must have a cause. Is this true? Or rather, must this be true?

If you think about it rationally, it makes intuitive sense that something cannot come from nothing. After all, the idea that anything can come from nothing sounds absurd; if it could, it would completely undercut the notion of cause and effect that we so thoroughly experience in our day-to-day lives. The idea of creation ex nihilo, or from nothing, violates our very ideas of common sense.

But our day-to-day experiences are not the sum total of all that there is to the Universe, and our ideas about common sense don’t necessary transfer into realms in which the lessons learned from our everyday experiences don’t apply. There are plenty of physical, measurable phenomena that do appear to violate these notions of cause and effect, with the most famous examples occurring in the quantum Universe. As a simple example, we can look at a single radioactive atom. If you had a large number of these atoms, you could predict how much time would need to pass for half of them to decay: that’s the definition of a half-life. For any single atom, however, if you ask, “When will this atom decay?” or, “What will cause this atom to finally decay?” or even, “What will cause the emergence of the decayed state?“ there is no cause-and-effect answer.

In a traditional Schrodinger’s cat experiment, you do not know whether the outcome of a quantum decay has occurred, leading to the cat’s demise or not. Inside the box, the cat will be either alive or dead, depending on whether a radioactive particle decayed or not. If the cat were a true quantum system, the cat would be neither alive nor dead but in a superposition of both states until observed. However, you can never observe the cat to be simultaneously both dead and alive.

From a particle physics point of view, you may be able to point to something like “the emission or exchange of a certain virtual particle” as the underlying cause, but that doesn’t do anything to tell you when the exchange will occur, or what triggered that exchange at one particular moment rather than at any other one. There are indeed physical actions you can take that would force an atomic nucleus to split apart; you can get the same effect with a deliberate, concrete cause behind it. If you were to fire a particle at the atomic nucleus in question, for example, you could trigger its splitting apart and releasing energy. However, the phenomenon of radioactive decay forces us to reckon with this uncomfortable fact:

The same effect that we can achieve with an instigating cause can also be achieved, naturally, without any such instigating cause at all.

In other words, there is no cause for the phenomenon of when this atom will decay. It is as though the Universe has some sort of random, acausal nature to it that renders certain phenomena fundamentally indeterminate and unknowable. In fact, there are many other quantum phenomena that display this same type of randomness, including entangled spins, the rest masses of unstable particles, the position of a particle that’s passed through a double slit, and so on. In fact, there are many interpretations of quantum mechanics — paramount among them the Copenhagen Interpretation — where the lack of causality is a central and unavoidable feature of nature, not a “bug” in its workings.

Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum. (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero. If there are additional particles or fields beyond what the Standard Model predicts, they will affect the quantum vacuum and will change the properties of many quantities away from their Standard Model predictions. However, the QCD contribution cannot be calculated perturbatively, the way electromagnetism can.

You might argue, and some do, that the Copenhagen Interpretation isn’t the only way to make sense of the Universe and that there are other valid interpretations of quantum mechanics that are completely deterministic. While this is true, it’s also not a compelling argument; the viable interpretations of quantum mechanics are all observationally indistinguishable from one another, meaning they all have an equal claim to validity. You cannot simply choose the interpretation you like, or the one that supports you preferred conclusions, and declare “this is correct while all others are irrelevant.” That’s not how you “prove” anything at all: not logically and certainly not scientifically.

There are also many phenomena in the Universe that cannot be explained without ideas like:

• virtual particles,
• fluctuations of (unmeasurable) quantum fields,
• and a measurement device that forces an “interaction” to occur.

We see evidence of this in deep inelastic scattering experiments that probe the internal structure of protons; we predict that it needs to occur in order to explain black hole decay and Hawking radiation. To assert that “whatever begins to exist must have a cause” ignores the many, many examples from our quantum reality where — to put it generously — such a statement has not been robustly established. It may be possible that this is the case, but it is anything but certain.

However, that’s only the first “step” in the argument; there are others to consider as well.

Our Universe, from the hot Big Bang until the present day, underwent a huge amount of growth and evolution, and continues to do so. Our entire observable Universe was approximately the size of a modest boulder some 13.8 billion years ago, but has expanded to be ~46 billion light-years in radius today. The complex structure that has arisen must have grown from seed imperfections of at least ~0.003% of the average density early on, and has gone through phases where atomic nuclei, neutral atoms, and stars first formed.

Did the Universe, which exists, have a moment or event where it began to exist?

This one is, believe it or not, even more dubious than the prior assertion. Whereas we can imagine that there is some fundamentally deterministic, non-random, cause-and-effect reality underlying what we observe as the bizarre and counterintuitive quantum world, it is very difficult to conclude that the Universe itself must have begun to exist at some point.

I can already hear you objecting, “But what about the Big Bang?”

That’s what they all say, right? Isn’t it true that our Universe began with a hot Big Bang some 13.8 billion years ago?

Kind of. Yes, it is definitely true that we can trace the history of our Universe back to an early, hot, dense, uniform, rapidly expanding state. It is true that we call that state the hot Big Bang. But what’s not true, and has been known to be not true for some 40+ years, is the notion that the Big Bang is the beginning of space, time, energy, the laws of physics, and everything that we know and experience. The Big Bang wasn’t the beginning but was rather preceded by a completely different state known as cosmic inflation.

In the top panel, our modern Universe has the same properties (including temperature) everywhere because they originated from a region possessing the same properties. In the middle panel, the space that could have had any arbitrary curvature is inflated to the point where we cannot observe any curvature today, solving the flatness problem. And in the bottom panel, pre-existing high-energy relics are inflated away, providing a solution to the high-energy relic problem. This is how inflation solves the three great puzzles that the Big Bang cannot account for on its own.

Although many still treat inflation as a speculative theory, that’s certainly not fair, on scientific grounds, here in the 21st century. There is an overwhelming set of evidence for this, which includes:

• the (almost, but not perfectly, scale-invariant) spectrum of density imperfections that the Universe exhibited at the onset of the hot Big Bang,
• the existence of those overdense and underdense regions on super-horizon cosmic scales,
• the fact that the Universe exhibited completely adiabatic, and no isocurvature, fluctuations at the earliest times,
• and the fact that there is an upper limit to the temperatures achieved in the early Universe that is well below the Planck energy, which is the scale at which the laws of physics break down.

Cosmic inflation corresponds to a phase of the Universe where it was not filled with matter and radiation, but rather it had a large, positive energy inherent to the fabric of space itself. Instead of getting less dense as the Universe expands, an inflating Universe maintains a constant energy density for as long as inflation persists. That means instead of expanding and cooling and slowing in its expansion, which the Universe has been doing since the start of the hot Big Bang, the Universe was, prior to that, expanding exponentially: rapidly, relentlessly, and at an unchanging rate.

How matter (top), radiation (middle), and dark energy/inflationary energy (bottom) all evolve with time in an expanding Universe. As the Universe expands, the matter density dilutes, but the radiation also becomes cooler as its wavelengths get stretched to longer, less energetic states. Dark energy’s (or inflationary energy’s) density, on the other hand, will truly remain constant if it behaves as is currently thought: as a form of energy intrinsic to space itself. These three components, together, dictate how the Universe expands at all times from the Big Bang until the present day and beyond.

This represents a tremendous change to our picture of what the beginning of things looked like. Whereas a Universe filled with matter or radiation will lead back to a singularity, an inflating spacetime cannot. Not just “may not” but cannot lead to a singularity on its own. Remember, fundamentally, what it means to be an exponential function in mathematics: after a certain amount of time, whatever you have will double. Then, when that same amount of time passes again, it doubles again, and with each elapsing moment it continues to double. It does this again and again, so on and so on, without bound, for as long as the exponential behavior remains.

That same logic can be applied to the past: that same amount of time ago, for as long as the exponential behavior was in place, whatever we had back then was only half the amount of what we have now. Take another, equivalent timestep backward, and it is halved once again. But no matter how many times you halve and halve and halve whatever you had initially, it will never reach zero. That’s what inflation teaches us: our Universe, for as long as inflation went on, can only get smaller but can never reach a size of zero or a time that can be identified as the beginning. There is no point that an exponentially increasing quantity (or, if we extrapolate backwards to the past, an exponentially decreasing quantity) ever emerged from “zero” in the past.

In other words, inflating spacetimes cannot emerge from a singularity, or an “event” that corresponds to a unique origin.

Blue and red lines represent a “traditional” Big Bang scenario, where everything starts at time t=0, including spacetime itself. But in an inflationary scenario (yellow), we never reach a singularity, where space goes to a singular state; instead, it can only get arbitrarily small in the past, while time continues to go backward forever. Only the last minuscule fraction of a second, from the end of inflation, imprints itself on our observable Universe today. The size of the now-observable Universe could’ve been no smaller than about 1 cubic meter in volume at the start of the hot Big Bang.

Unfortunately for us, in scientific terms, we can only measure and observe what the Universe gives us as measurable and observable quantities. For all the successes of cosmic inflation, it does something that we can only consider unfortunate: by its nature, it wipes out any information from the Universe that existed prior to inflation. Not only that, but it eliminates any such information that arose prior to the final tiny fraction-of-a-second just before the end of inflation (somewhere around the final ~10^-32 seconds of inflation), which preceded and set up the hot Big Bang. To assert that “the Universe began to exist” is a possibility, one that could be true if a hitherto undiscovered pre-inflationary state emerged from a singularity. But to assert that “the Universe must have begun to exist” is completely unsupported, both observationally and theoretically.

It’s true that, about 20 years ago, there was a theorem published — the Borde-Guth-Vilenkin theorem — that demonstrated that a Universe that always expands cannot have done so infinitely to the past. (It’s another way of expressing past-timelike incompleteness.) However, there is nothing that demands that the inflating Universe be preceded by a phase that was also expanding. There are numerous loopholes in this theorem as well: if you reverse the arrow of time, the theorem fails; if you replace the law of gravity with a specific set of quantum gravitational phenomena, the theorem fails; if you construct an eternally inflating steady-state Universe, the theorem fails.

Again, as was the case with the first point of the Kalam cosmological argument, a “Universe that came into existence from non-existence” is a possibility, but it is neither proven nor does it negate the other viable possibilities.

The modern cosmic picture of our universe’s history begins not with a singularity that we identify with the Big Bang, but rather with a period of cosmic inflation that stretches the Universe to enormous scales, with uniform properties and spatial flatness. The end of inflation signifies the onset of the hot Big Bang, with the conventional “13.8 billion year history of the known Universe” taking place in the aftermath of that event.

And now, after reckoning with the first two steps of the Kalam cosmological argument, we come to the third and final one: the Universe itself has a cause to its existence, and that cause must be God.

We’ve already established that the first two premises of the Kalam cosmological argument are, at best, unproven. If we assume that they are, nevertheless, true, does that establish that God must be the cause of our Universe’s existence? That is only defensible if you define God as “that which caused the Universe to come into existence from a state of non-existence.” Here are some examples that show why such a definition is absurd.

• When we simulate a two-dimensional Universe on a computer, did we bring that Universe into existence, and are we, therefore, the God(s) of that Universe?
• If the Universe’s inflationary state arose from a pre-existing state, then is the state that gave rise to inflation the God of our Universe?
• And if there is a random quantum fluctuation that caused inflation to end and the hot Big Bang, or the Universe as we know it, to begin, is that random process equivalent to God?

Although there would likely be some who argue in the affirmative, that hardly sounds like the all-powerful, omniscient, omnipotent being that we normally envision when we (or, more importantly, proponents of the Kalam cosmological argument) talk about God. If the first two premises are true — and remember, they have not been established or proven to be true — then all we can say is that the Universe has a cause; not that that cause is God.

From inflation to the hot Big Bang, to the birth and death of stars, galaxies, and black holes, all the way to our ultimate dark energy fate, we know that entropy never decreases with time. But we still don’t understand why time itself flows forward. However, we’re pretty certain that entropy, and the thermodynamic arrow of time, cannot be the answer.

There’s an important lesson to learn from this, and not the one that those who put forth or support the Kalam cosmological argument intended: it is fundamentally unscientific to try and use pieces of scientific data to support whatever position or conclusion you would prefer. Science is about collecting data, and then using the full suite of that data responsibly to stress test the various hypotheses that remain viable. You absolutely must not begin from the conclusion you hope to reach and work backward from there. That is antithetical to any knowledge-seeking enterprise to assume the answer ahead of time.

Instead, the responsible path would be to formulate your assertions in such a way that they can be scrutinized, tested, and either validated or falsified. In particular, you cannot posit an unprovable assertion and then claim you have “proved” the existence of something by deductive reasoning. If you cannot prove the premise (or the underlying assumptions behind the premise), all logical reasoning predicated upon that premise is unsubstantiated.

It remains possible that the Universe does, at all levels, obey the intuitive rule of cause-and-effect, although the possibility of a fundamentally acausal, indeterminate, random Universe remains in play (and, arguably, preferred) as well. It is possible that the Universe did have a beginning to its existence, although that has by no means been established beyond any sort of reasonable scientific doubt. And if both of those things are true, then the Universe’s existence would have a cause, and that cause may be (but isn’t necessarily) something we can identify with God. However, possible does not equate to proof. Unless we can firmly establish many things that have yet to be demonstrated, the Kalam cosmological argument will only convince those who already came predisposed to agree with its conclusions, irrespective of whether they’ve been proven or not.

A version of this article was initially published in November of 2021. It was updated in 2025.