One of the most interesting answers I often get in response to this argument goes like this: "Well, maybe it is true that you can't have an infinite past, but how do we know the past really exists at all?" I think the hope being expressed in this argument is that if we don't have a real past, there is no need to trace our current state of the universe back to prior causes, meaning that we don't need a First Cause--God. If this is the hope, it is a vain one, for even if the past did not exist there would be many other features of the world that still point necessarily to the existence of God. Every feature of the world points to the existence of God!
But right now I am more interested in the idea expressed by the argument--that maybe the past does not exist. I don't think that anyone who actually raises this idea ever really takes it seriously. It is just a desperate attempt to find something to grasp onto that might seem to negate the need for God. But what exactly is even meant by the idea that the past does not exist? Is this a meaningful or a reasonable possibility? Perhaps a fictional dialogue might bring out the issues here:
"Maybe the past isn't real at all. Maybe it doesn't exist, and there is no past, but only the present."
"But it is obvious the past exists. The past is simply the previous events in a timeline which form a narrative of history leading up to the present. Isn't it self-evident that we live in a universe where there is such a preceding sequence of events? Doesn't everything in the present testify to a past narrative leading up to this present moment? To deny the existence of the past involves denying things like the existence of the year 1929, and isn't this evidently absurd and false? Isn't it obvious and evident that there is such a thing as the year 1929, and that it is a part of a narrative sequence that leads up to this present moment?"
"Well, in that sense, yes, of course there is a past. But what I am saying is, What if this past is nothing more than an illusion? What if it looks like there has been a past, but there never really was one? What if our memories of a past, and all the appearances that there has been a past, are illusory?"
"I'm not sure exactly what that means. It seems to me that the past is nothing more than a narrative history. Since we both grant that it is evident that there is such a narrative history, isn't that the same as saying that there really is a past? What exactly would be the difference between an illusory past and a real past?"
"An illusory past would be when you have a narrative history (such as ours which includes the year 1929), but it never actually happened. That is, only the present is really real. All that really exists is this present moment frozen in this state, not having ever been anything else or ever going to be anything else. There is a narrative history, but the flow of time itself is just an illusion. There is no flowing. We are really just standing still in this present moment, with all our illusory memories, etc. That's what I mean by the idea of the past as illusory. Why couldn't this be the case? How would we know if it is or isn't the case?"
"OK, so in your terminology, a real past would be a past that is not just a narrative history but where there is a real flow of time from the past to the present and into the future, while an illusory past would be when we have a narrative history, but reality is actually frozen in the present, with no actual movement from the past to the future. Am I getting this right?"
"Yes, that's basically it."
"I think there is a problem in your idea of there being a contrast between reality being 'frozen' in the present as opposed to 'moving' through time. Perhaps an analogy might bring out this problem: Think of a recorded TV show. It can be playing, in which case the show is moving through its individual frames and changing, going from the beginning towards the end. Or, the TV show recording could be paused, in which case it is just sitting there, frozen, not moving towards the end. This seems analogous to the distinction you are making in connection with real history. But if you think about the TV recording, you realize there is something else required to be in that scenario to make sense of the distinction between being paused and un-paused. I wonder if you see what I am getting at?"
"I'm not sure I do."
"Well, in order to talk about the TV program being paused, we have to think of that pausing as taking place in the context of an experience of time that isn't paused. That is, it only makes sense to say that the TV recording is paused or frozen if the world around it isn't paused or frozen, if things are still going on around it while it sits there unmoving. In short, the very idea of something being 'paused' or 'frozen' involves a context of an un-paused, flowing time."
"OK, I see what you mean."
"But that is a problem for your idea of time itself, so to speak, being 'paused' or 'frozen' in the present, as opposed to 'flowing' through time. If time itself is 'paused,' what is it paused in relation to? You would have to imagine our universe as being like the TV recording, being frozen and unmoving in relation to a world that is not frozen going on all around it. In other words, for time to be frozen, it would have to be in the context of a time that isn't frozen, which means that, really, time isn't frozen at all. Really, a paused TV recording isn't frozen in time. It, too, is moving through time. It is changing in terms of its relationship to the things around it. To say it is frozen is not to say it is not going through time but only that it is doing so in a way that doesn't involve much, if any, individual movement."
"OK, I think I see what you are saying. You are saying that the very concept of time being 'frozen' as opposed to 'moving' contains an absurdity, because something can only be 'frozen' in the context of time going on all around it. Therefore, time itself cannot be frozen, because it could have no un-frozen context to be frozen in relation to."
"Yes, that's it exactly. And the conclusion is that there is no meaningful distinction between time considered as 'frozen' or 'unmoving' and time considered as 'moving' or 'flowing.' And since your very idea of the distinction between 'illusory' and 'real' time is based on this other nonsensical distinction, it too is meaningless and nonsensical. There can really be no distinction between 'illusory' and 'real' time in that sense. Time is nothing more than simply the idea of having a timeline that connects the state of things in the present with a history in the past and, perhaps, a series of events in a future. This narrative history simply is what it means to have a past, and there can be no meaningful distinction between thinking of it as 'flowing' or as 'static.' So if we have this narrative history at all, then it is real history. And therefore, it is self-evident that the past really exists, because it is self-evident that this present moment has a narrative history."
"I see your point. But could there be some other way in which we could meaningfully speak of an illusory past?"
"Sure. Let's say that the earth and all of us really came into being five minutes ago, created by a race of superior alien beings. But when they created us, they made the world look as if it had a history it never really had, and they implanted memories in us of things that never really took place. In this case, we would meaningfully say that the past that exists in our memories is not the real past; it is an illusory past, because it is not what really happened. That is, it is not the true narrative history of our world, but only appears to be such."
"Well then, couldn't it still be possible that there is no real past, that the past is truly illusory? For how do we know that something like your scenario with the aliens hasn't actually happened? Isn't it possible that aliens have created us right now in this present moment, and we didn't really exist before this moment at all but only think that we did because false memories have been implanted in us?"
"Let's think about that more closely. If the aliens created us just now when we didn't really exist before, then don't we still have a real past--namely, one in which we didn't exist before and then the aliens created us and implanted false memories in us? So this scenario doesn't make it illusory that there has been a past; it only makes the particular past we remember illusory. So there is still a real past."
"Yes, I see what you mean. In fact, the more I think about it, I begin to realize that your previous arguments against my earlier attempt to talk about an illusory past are going to apply really to any attempt to say that there is no past at all, that the whole idea of a past in general is illusory. Because as soon as I try to make a distinction between the idea that the past is real on the one hand, and on the other hand that the past is not real--implying that we came into being just now and didn't exist before--I run into the problem that the very idea of 'not existing before' creates a new real past to replace the illusory one. The only way I can call any particular past illusory is to contrast it with a past that is not illusory. I must say, 'This series of events is not what really happened, because this other series of events is what really happened.' Without some past that really happened to contrast it with, there would be no meaning in calling any particular past 'illusory.'"
"Exactly. So as long as it is self-evident that our present moment is part of a narrative history that contains earlier events in a timeline, we must say that the past is real, and it makes no sense to say that it is illusory. Therefore, we can say with full confidence that the past is certainly real."
"So it would seem!"