Topics Time

Question How long is forever? I know this question is ambiguous, but I have often tried to understand the heavy anchor of time and infinity, but I think it's really just too big to understand with the tools I've been given. I would really like to know someone's thoughts on the subject, and if the question is too ambiguous, is it because we don't have the 'brain power' to understand?

Accepted:
July 30, 2007

Comments

Time is a sequence of distinct moments, one after another, such that the universe has (or at least could have) a different state at each one. We understand time from the perspective of the present moment, the one at which our thoughts are occuring. On the basis of our memory, we know that there were other moments before this one, because we remember that things used to be different from how they now are, and any such change must have involved a passage of time. Our expectations lead us to believe that there will be moments of time after the present. Such a belief is not utterly indefeasible -- everything could just suddenly stop -- but it seems a pretty safe bet.

Looking at things from the perspective of the present moment, it's not so very hard to conceive that either the past or the future could be infinite (though it's for the physicists, or perhaps the theologians, to decide whether either actually is). We can easily think about a time one year ago, and a time two years ago, and a time three years ago, and so on. The supposition that the past extends infinitely far back amounts to nothing more than the supposition that there is no number n such that we cannot think of a moment n+1 years ago. And likewise for the future: we just need to contemplate a sequence of moments extending forward from the present, and observe that there is no necessity that such a sequence should not just carry on going, with an additional moment beyond any particular moment we might happen to think of.

A related concept, but one that is worth keeping separate from this one, is that of eternity. When people talk about eternity, they do often just mean this infinite succession of moments: but there's another sense of 'eternity' which is rather more profound. Many theologians have theorised that God is eternal in the sense that He is somehow 'outside' time. There is no succession in God, they say, meaning that He does not pass through a sequence of different states. He sees the whole duration of the created universe, with its various different states, all together at once. If He sees fit to do one miracle in, say, the year 1 AD and another in 2007, He can perform both in one simple act, without having to wait for the intervening time to pass. This is certainly a harder notion to get one's head around than that of an everlasting sequence of distinct moments of time, but it's arguably a more intriguing one too.

And actually we don't have to get into contentious theological issues: something similar can be said of mathematical objects. Does the number seventeen exist now? Well, in a sense, we'd surely have to say it does. Did it exist thirty years ago? In the same sense, certainly. Numbers aren't the sorts of things that can come into being. But now compare this to the case of an ordinary physical object, or even a thinking being like a person. Do I exist now? I think so (therefore I am!). Did I exist thirty years ago? Yes: I was four years old. But I was very different then. I was quite a bit shorter, for a start. Has the number seventeen undergone any similar change? It doesn't seem that it has, or even that it could. My own existence has been a successive one, involving what philosophers would call different 'temporal parts', existing at different moments. Just as I can have different qualities in different spatial parts of myself, hair on the top part and toes on the bottom part, so too can I have different qualities in different temporal parts of myself, moderately tall in the 2007 version of me and really rather short in the 1977 version. But numbers don't seem to involve any such succession. Not only have they always existed, and will always exist, but they are completely immutable, permanently present in their simple entirety.

You might ask: "How long is this performance going to last?" And you might get the answer: "Two hours." You might also ask, more ambitiously, how long is this universe going to last?" And you might get the answer (from physicists presumably): "Forever." Now, those two answers seem similar; certainly they are grammatically similar responses to the two questions. And this might encourage you to think that "Forever" picks out a specific temporal duration, just as "two hours" does -- except that the first duration is a lot longer than the second. And then you might start to get a real headache trying to understand the nature of this duration "forever".

But, that's not what "forever" means here. To say that the universe will last forever doesn't mean that there's some really big temporal interval, forever, during which it will be around; it means rather that there is no last temporal moment of the universe. So there is no really big temporal quantity of foreverness that you have to wrap your mind around. What you have to understand rather is the thought that no matter where you are in the universe, temporally speaking, there are later moments of time in its life as well.