My cat Petra is good at many things. She’s quite the expert at teleporting from one room to another (she’s that fast). She knows how to manipulate—she gets fed whenever she wants, really. She usually wins the play fights against her sister Ollie, the slower (dumber?) one. Most of all, she’s good at winning my attention.
But Petra’s also good at proving God.1 Here’s how.
First off, let’s acknowledge that in all of reality, there are only two possibilities: Either everything is dependent on something else for its existence, OR one or more things is not dependent on anything else for its existence. Put another way, all of reality either is made up of only conditioned realities, or all of reality includes one or more unconditioned realities. Both of these possibilities cannot be true, for they exclude each other.
Insert Petra. Obviously, Petra is a conditioned reality. That is, she depends on other things—other realities—for her existence. As a cat, she depends on organs, cells, molecules, protons and neutrons, and so on—all of which, too, are dependent on other realities. Quite simply, as much as I love her, Petra does not exist necessarily: She very well could not have existed. Even now, she depends on various realities to sustain her in existence.
But here arises the crucial question: Does Petra rely on only conditioned realities for existence?
Suppose she does. If so, then Petra depends on either a finite or infinite amount of conditions. A finite amount of conditions would mean there is a last condition, or a condition that is most fundamental. However, we are still talking about conditioned realities—things that depend on other things. So this last or most fundamental condition would essentially be a conditioned reality whose conditions are never met, and therefore nonexistent. But that’s nonsensical. If the last condition didn’t exist, then neither would Petra. But Petra quite obviously (and quite obnoxiously) does exist!
Okay, so what about an infinite number of conditions? Would that solve the problem? If Petra depended on an infinite number of conditions for her existence, then there would be no last or fundamental condition. Instead, there would always be one more condition left to be achieved. But if that were the case, the conditions would be unachievable, and Petra still wouldn’t exist.
So where does that leave us? If neither a finite nor infinite number of conditions is sufficient for Petra’s existence, then there cannot be only conditioned realities in all of reality. The alternative—that there is one or more unconditioned reality—must be the case.
Remember at the beginning, we said there were only two options. Either all of reality is explained by only conditioned realities—things that only exist because other things exist—or all of reality also has one or more unconditioned reality, something whose very nature is to exist. We ruled out the former, so there must be at least one unconditioned reality in all of reality.
At least one. But can there be more than one unconditioned reality? Pretend there are two. If so, then there must be some distinguishing feature between the two (or else they would be the same thing). Whether the difference is in “form,” like the difference between a rabbit and a human or in “matter,” like two different humans, or a difference in location, or in power, or whatever other difference there may be, there would have to be some distinctive feature between them.
Now, if there were some distinguishing feature, then that would imply a limit to one—or both—of these realities. But if limited, then such a reality would be conditioned by something outside of it in order to explain its distinctive element. After all, since these two unconditioned realities supposedly share a common nature, there must be some external cause that “combines” the common nature with the distinguishing feature. But then the alleged unconditioned reality would NOT be an unconditioned reality, for its existence would depend on something external to it!
Therefore, there can only be one unconditioned reality. And since there must exist unconditioned reality for anything else to exist at all (like dear Petra), then there does, in fact, exist one and only one unconditioned reality.
As hinted at in the above argument, this unconditioned reality cannot have any limits. Another way of saying this is that unconditioned reality must be purely simple: It cannot have any boundaries or restrictions. The nature of unconditioned reality is to exist. Any other distinguishing element would be arbitrary and conditioned on another reality. The unconditioned reality “just is”: It is the fullness of being itself.
A limit implies potential, but there can be no potential with unconditioned reality. I can say that my canvas has the potential to be a masterpiece—once I labor over it with the best oil paints. But here the canvas receives something from outside itself. Unconditioned reality cannot be like that. To say unconditioned reality has potential in some manner would mean that it is able to also actualize itself in that manner. In other words, it would have to receive the actuality while already having it. Doesn’t make sense!
If unconditioned reality is wholly actual, with no potential, then it is consequently unchangeable. Right away, then, we can say a few things about what unconditioned reality is not. It is not any physical reality, for physical reality is subject to change. Matter involves non-being. It exists in a state of becoming. But unconditioned reality cannot be like that; it simply is—and fully so. Similarly, unconditioned reality is not dimensional in any way. Neither can it be in time—at least not as we usually understand it, for changeable things are subject to time.
So unconditioned reality is not any one part of the physical Universe. It also can’t be any combination of physical realities—even the entire Universe itself.
The one unconditioned reality is non-physical, infinite (or limitless), fully actual, eternal (outside of time), being itself. In addition, because all else that exists ultimately depends on the one unconditioned reality for existence, then this reality is none other than the “creator” of the Universe.
 This is not offered as a proof in the strict scientific sense, but it represents a strong—and traditional—philosophical argument nonetheless. I owe much to the book New Proofs for the Existence of God by Robert Spitzer and Who Designed the Designer? by Michael Augros.