It’s commonly accepted now that the universe as we know it had a beginning in time, with the physical universe having spontaneously expanded from an infinitely small point some time in the vicinity of 14 billion years ago, in what is colloquially referred to as the “Big Bang.”

Prior to the establishment of the Big Bang as the predominant understanding of the universe’s beginnings, the predominant view among cosmologists was Steady State theory, the idea that the universe is infinitely old and has existed in essentially its present state infinitely far back into the past. In fact, the Big Bang had quite a hard time becoming the predominant theory because of a pervasive bias in favor of an infinitely old universe among cosmologists, driven by their atheistic prejudices, and won the day only because the evidence for it was quite strong and hard to avoid.

Even long after the theory’s establishment, and still to some degree today, many cosmologists looked for workarounds, such as “big crunch” theories according to which the universe cyclically contracts to almost-a-singularity before expanding again, or various flavors of multiverse theory according to which each universe spawns others somehow. None of these have panned out, having been either empirically disconfirmed or empirically untestable in principle

The idea of an infinitely old universe is not a recent development. Aristotle (though a theist and anti-naturalist) believed in it, and Aquinas, while believing on the basis of divine revelation that the universe had been created with a beginning in time, nevertheless agreed with Aristotle that an infinitely old universe could not be disproven by reason.

This, I believe, was a rare fumble by Aristotle and Aquinas. I believe that the idea of an infinite universe can be shown to be false, or at least unintelligible, through philosophical reasoning accessible to all, and I will attempt to outline that reasoning here.

To understand why the past cannot extend infinitely backwards in time, let us first examine that direction of time that IS uncontroversially unbounded: the future. The future can, and most would agree will, continue on forever and ever, and yet this doesn’t present any logical conundrums in most people’s minds. Why is this?

The reason is that the future is only potential. Things that will happen in the future have not happened yet. They do not yet exist as actual events that have occurred. This is by contrast to events that happened in the past, which have actually happened already and cannot be changed.

As a consequence of this, the future is always approaching infinity but never actually getting there. No matter how much time passes, there will never be a time in the future in which anyone will be able to look back and correctly say that an infinite amount of time has passed since the moment in which you are reading this. Be it a million, a billion, a trillion, or a trillion trillion years from now, the amount of time between right now and any moment in the future will always be finite.

By contrast, the idea of an infinitely old universe entails that an infinite amount of time has already passed in this universe, which entails that there are moments that happened infinitely long ago in the past. Now, as we have just seen, there will never be a moment that is infinitely far in the future, and hence there will never by a time in the future where the present moment in which you are reading this will be infinitely distant in the past. The present moment (as well as all moments in the finite past) and all future moments will be separated by a finite amount of time.

Thus, to say that some moment in time is infinitely far in the past, and that the present is infinitely far into the future from that moment is to assert a fundamentally different sort of relationship between those moments than what we normally mean by “past” and “future,” specifically a sort of relationship that cannot occur through the passage of what we normally mean by time.

This by itself is sufficient to demonstrate that whatever it is that we mean if we assert that the universe is infinitely old, and hence that there are moments that occurred infinitely far back in the past, we are not making an intelligible statement about time as we know it. Such assertions are at best a change of subject rather than statements about what we normally mean by time. Time as we know it - that phenomenon that we refer to when we discuss time - cannot extend infinitely back into the past any more than a circle cannbe a square. Those of you who just wanted an argument for why the past cannot be infinite can stop reading here.

However, for those of you willing to tolerate more abstruse reasoning, I think there is more of interest that can be said here. We’ve seen that time as we know it cannot be infinite in the past, and that statements to the effect that the past is eternal are at best changes of subject. But can they be construed in such a way that they mean anything coherent at all? Is there anything related to time as we know it, and to the past as we know it, that could be infinite in a way that the past cannot? I think there is.

Time, Change, and Causality

If we think about it a bit, we can see that this finite relationship between any two moments in time is part of what it means to say that two events are related in time, that one is in the future of the other.

To see this more clearly, let us examine the nature of time itself. Time is the passage of change. And what is change? Change is the procession of cause and effect. Change occurs as causes cause effects to happen, followed by those effects being causes that cause more effects to happen, and so forth.

Hence, when we say that one event or moment occurs after another one in time, when we say that one moment is in the future and another in the past, what we are actually asserting is a relationship of causal dependence between the two moments. That is, we are stating that the future moment is causally dependent upon the prior one.

So, to give one example, my middle name is Bradford. On my driver’s license and passport, it says “Bradford.” On my birth certificate, it says “Bradford.” My credit cards have B as the middle initial. What accounts for all these phenomena? They are all effects that were caused by my parents deciding to give me Bradford as my middle name when I was born.

Take any of these events - the printing of “Bradford” on my birth certificate and ID cards, the printing of “B” on my credit cards, you reading that my middle name is Bradford right now, and so on - and each of these events traces backwards in time through a chain of finite causes to the moment and event in which my parents decided that Bradford would be my middle name. All of these events are causally dependent on that event that occurred in a past moment.

Indeed, this sort of causal relationship is simply what we mean when we say that any two moments or any two events are related in time. When we say that a particular moment is in the past, we mean that the way things are now is causally dependent via chains of cause and effect on the way things were at that prior moment. When we say that a particular event happened in the past, we mean that there is a chain of cause and effect from that event to some events in the present (for instance, our learning about the event). When we say that some moment or event will occur in the future, we are predicting that it will be caused to be that way by the way things are now through a chain of cause and effect.

To illustrate this point more clearly, let’s do a thought experiment. Imagine that there is an actually real alternate universe which is completely isolated causally from ours. That is to say, nothing in that alternate universe causes anything to happen in ours or vice-versa. There is no possibility of anyone in that universe (assuming there is anyone in that universe) gaining any knowledge of ours, nor of anyone in ours gaining any knowledge of that universe, because gaining such knowledge would require something about the one universe to have effects that could be observed in the other, which for our thought experiment can’t happen.

Given this scenario, how would you relate events in that universe to events in ours temporally? For instance, let’s say that in this alternate universe, a star that is similar to our own sun comes to exist. How would you determine whether that star formed after or before our own sun? Our own sun is estimated to have come into existence around 4.6 billion years ago, or in the neighborhood of 9 billion years after the Big Bang. How would you relate that temporally to events in the other universe?

You might be tempted to say that if the sun in this other universe came to exist only 5 billion years after that universe’s Big Bang (assuming the other universe started with a Big Bang) that their sun came to exist before our sun. But upon a bit of reflection, that is clearly a nonstarter, because a year refers to a measurement that only exists in our universe, namely the amount of time it takes for our earth to make a full revolution around our sun. All other temporal metrics we have likewise rely on changes that occur in our universe. Without any causal interaction between the two universes, there is no way to relate the revolution of our planet (or any other event in our universe) to anything in the other universe.

You might be tempted to say that a “year” in the other universe is determined by the amount of time that subjectively feels to people in that universe to be the same as how the passage of a year subjectively feels to people in our universe. But of course this is a subjective impression, not an objective metric, and it varies wildly not just from person to person but from year to year within the same person. Certainly years seem to pass more quickly than when I was a child, and if I were to fall into a coma for a year, it would seem to pass even more quickly. And of course such an idea relies on the assumption that there are people in the other universe.

And even if you could meaningfully apply the concept of a “year” to the other universe, the conclusion that 5 billion “years” after their Big Big is “before” 9 billion years after our Big Bang presumes that the two Big Bangs happened at exactly the same time, but without any causal interaction between the two universes, there is simply no basis on which to make that assessment.

The only way that anything in the other universe could be temporally related to anything in our universe is if, contrary to our thought experiment, there were causal interaction between the two. So, for example, if someone in that universe were to somehow make contact with someone in our universe, and then someone in our universe were to respond back, and then someone in that universe were to respond to that, and so on, then we could say that the initial contact happened before the response, and that the second response happened after the initial response, and so on. But in this case, we aren’t really talking about two different universes after all, but one universe with one timeline.

All of this brings us back to my initial point: When we talk about time, we are really talking about the passage of change and the chains of cause and effect that bring about change. All temporal concepts, such as “before,” “after,” “past,” “future,” and so forth are references to chains of causal dependency, and are meaningless apart from causal dependency. To state that something happened or will happen before or after something else is implicitly to make a claim about the order of causal dependency, and has no meaning apart from that.

Change And Finiteness

We can also see that the chains of cause and effect that link moments in time must be finite. What do I mean by that and why do I say it? To say that some moment in the future will be causally dependent on the present moment is to say that the different state of things in the future - everything in that future moment that will be different from the way things are in the current moment - will come into existence as an effect of causes acting in the current moment producing changes to the way things are now. In other words, everything different about the future will have a beginning in time and be causally dependent on something else - hence finite.

Likewise, the causes inside our universe that are acting in the present moment to effect future moments are also finite, because they are themselves effects of causes acting in previous moments, which were the effects of causes acting in moments prior to that, and so on.

I’ll give a concrete example to illustrate why this is so: This essay that you are reading right now exists because I wrote it in the past. Hence, both this essay’s existence and your own state of reading it are effects of me having written it, hence they have a beginning in time and are causally dependent on me writing it in the past, hence are finite.

But as I sit here writing this essay (switching now to my point of view as I am writing this in what is now your past), I am myself changing. I have changed from being a person who was not writing this essay earlier today into a person who is writing it now. Obviously this property of myself is itself an effect of change with a beginning in time that is causally dependent on past causes and therefore finite, otherwise this essay would’ve been completed infinity long ago. And the various causes in the past that have caused me to start writing this essay were themselves finite with a beginning in time, because they changed from not causing me to write it to causing me to write it. And so on and so forth.

Back To The Future

With all of this out of the way, we can see more clearly the underlying reason why, despite the future being infinite, there will never come a moment in time that is infinitely far in the future from the present moment. What makes any moment in our future a moment in our future is that it will be causally dependent on our present moment via a chain of finite causes and effects. And no matter how much you add together anything finite, including finite causes and effects, you will never reach an infinite amount of it.

To say that some moment is in our past is to say that the way things are now is causally dependent by finite chains of cause and effect on the way things were then. And likewise, no aggregate of such finite chains of cause and effect can possibly add up to an infinite number of them.

To claim that the past is infinite, and hence that there are moment(s) in time infinitely far in the past, and hence that our present moment has somehow gotten infinitely far away from such moments via chains of cause and effect, is to implicitly cease talking about time as we know it altogether, since it is impossible for any two moments in the same timeline to get infinitely far away from each other through the finite chains of cause and effect that comprise what we refer to as time.

What An “Infinite Past” Really Means

But to return to my earlier question, is there any kernel of something sensible or coherent that can be rescued from the idea of an infinite past? Is there anything related to the past that could be infinite? I think there is, and in fact it is something that is necessitated by the fact that time as we know it cannot be infinite in the past.

For if time as we know it must be finite in the past, hence there are no moments infinitely long ago, then there must be a first moment. So what can we deduce about the first moment in time as we know it?

Well, the first thing we can say is that the temporal universe at that first moment in time must have been caused to exist by something. Why? Here I refer back to my first essay in this series, and the first principle that nothing can’t cause anything.

However, what caused that first moment in time must have been fundamentally different from all the causes that act within time. Remember previously how I pointed out that when I began causing the essay you are reading to exist by writing it, I myself changed from not writing it in the moments before to writing it in that moment. Something new about me, the cause of the essay, was also caused to exist in time after not existing in previous moments. Recall that this is what I mean by saying that the chains of cause and effect in time are finite: They all begin in time and are causally dependent for their existence.

But that cannot be the case for the cause of the first moment in time as we know it. That is, the cause of the universe at the first moment in time cannot have changed from not causing it in the moment before to causing it, because that would contradict its being the first moment in time.

What that means is that the cause of the universe in the first moment must itself be unchanging and thus outside time. That first cause didn’t change from not creating the universe to creating it, but rather creates it eternally in a sort of eternal “now” as best we can conceive it. The causal act manifested in the first moment in time from our perspective, but is not itself in it. Since the first cause is not temporally finite in the manner we have described, it is infinite. That first causal act can be related by analogy to the past inasmuch as all events “after” it are causally dependent on it, though it had no temporalbeginning the way the past does. Thus, if the concept of an eternal past refers to anything intelligible, it refers to this: the temporal universe being created at the beginning of time by an infinite and eternal cause from outside of time.

Omnipotence

Is there more we can say about the cause of the universe at the beginning of time? I believe there is. Recall principles 2 and 3 (the principle of sufficient reason and the principle that anything that exists objectively cannot be reducible to anything else) from the initial essay, and the way that I pointed out that they work together in principle 4.

What do these tell us? Any objectively-existing causal power that exists in our universe must be possessed by the timeless and infinite cause of the first moment of our universe. So is intelligence a causal power that objectively exist in our universe? Well then, the first causes must possess intelligence.

Those Thomists and Aristotelians among you will note that the argument for a finite past ultimately ends up at the same place where the Thomistic-Aristotelean argument for the necessity of an Unmoved Mover or First Cause of every moment in time ends up.