My question here is, what, exactly, is “time”? What is the nature, or the essence, of time?
In trying to answer that question, I will begin with what is most obvious about time, and work my way towards what is more obscure, or more hidden. But, since time is something that each of us knows perfectly (since each of us is aware of every part of the idea expressed by the word, “time”), even what is most hidden about time will be something that is somehow apparent, and somehow known. It is only a matter of bringing that awareness out into the open, and making that idea as clear and as distinct as possible.
To begin with, then:
Time is composed of three parts: the past, the present, and the future.
The past is the part of time that came before the present.
The present is the part of time that exists now.
The future is the part of time that will come to be after the present.
Strictly speaking, the present is the only part of time that exists. For the past is what existed, while the future is what will exist. But neither of these are, in this moment.
“This moment” – “now” – “the present” – each of these is just a different way of saying the same thing.
If “it” is the present moment, then “it” is always now. But in reality, “this” moment is always different from the “this moment” that came before. The word “now” is just a pointer which means, “this moment, that I currently happen to be in.” But the moment that I do happen to be in – the actual moment in which I reside – is always different, in each present moment.
What is most obvious about time is that it is always flowing, and that we are never in the same moment twice.
Even though time is always flowing, the present moment is not actually “changing.” For in order for there to be a change, there has to be some substance S which endures throughout the change – which changes from one state to the next. For instance, in order for a body S to change its place from A to B, then that body S must endure throughout the change – it must continue to exist, in order for it to be at a place B, after it was at a place A.
But in time, there is nothing stable, or enduring. “It is always now” is only a truth of language – for there is no “now” that is a stable, enduring being. Instead, “now” never refers to the same thing twice, and what it does refer to is always passing out of being, and being replaced by something wholly new; “this moment” does not change, but merely ceases-to-be, as “this moment” now comes to replace it. In this endless flow of “nows,” there is no moment that endures, and nothing that changes from this into that. Hence, even though time is something that is always flowing, and always different from how it was before, the present moment is not actually a thing that changes. For there is no “now” which endures throughout the flow, and which could change from “this,” into “that.”
Likewise, and more generally, time is not the same thing as change. For even though there cannot be any change without time, there can be time without change.
There are two parts to this claim:
First, there cannot be any change without time.
Second, there can be time without change.
I will consider each of these claims in turn.
There cannot be any change without time.
For, if a thing changes, it must change from this, to that. But then, the changing thing must have been this in this moment (M1), and that in that moment (M2). For example: if a thing changes place, it must change from being in a place A, to being in a place B. But that means that it must have been in a place A at a moment M1, and then in a place B at a moment M2.
Thus, in order for a thing to change, it must exist in more than one moment, and these moments must come one after another.
But whenever there are a multiplicity of moments in some sequence or order, then there is also time.
Hence, in order for there to be change, there must be time – there cannot be any change without time.
But, there can be time without change.
For, it is entirely conceivable that a year could pass, or a hundred years, or a thousand years, without a single thing changing in the world. Not a likely event, of course – but a conceivable one.
Of course, if nothing changed, then this flow of time could never be perceived. But, even if it could not be perceived, it could still occur. For it is always logically possible for a moment M2 to follow after a moment M1, even if there is not a single difference between the world-state in M2 and the world-state in M1.
Hence, time is not the same thing as change. For even though there cannot be change without time, there can be time without change.
Likewise, and for the same reasons, time is not the same as motion.
For, since motion is just the change of the position of a body in space, time is not the same as motion, since time is not the same as change.
Likewise, since motion is just a kind of change, then there cannot be any motion without time, but there can be time without motion.
Thus, time is not the same as change, or as motion.
Just as there could be time without change, there could also be a flow of time even if no other beings were in existence. For it is logically possible for time to exist, and for one moment to come after another, without any of these moments having any content of any kind – without there being a single thing that “happens” inside of this flow of time.
In this respect, time is just the same as space. For just as space could exist even if there were no bodies in the world, so could time exist, even if it was the only thing in existence. Likewise, just as the whole material world exists in space, while being other than space, so does the whole world exist in time, while being other than time. Finally, just as space is what remains when you take away a body from the place that it resides in, so is time what remains when you take away the whole changing universe from the time in which it has been changing.
Hence, time is not the same as the beings that are inside of time. For by its very nature, time is something vast, empty, and flowing.
For the reasons above, time is not the same as our measurements of time, or as our thoughts about time. For even if we were not there to measure it, or to think about it, there would still be change in the world, and the flow of moments, with one coming after the next. Hence, there would still be Time.
We say: “Time,” and “Space.” In saying these words, we speak as if there is only one time, and only one space. But it is possible that there are actually many separate times, and many separate spaces.
For instance, imagine that there are two totally different universes, with two totally different times, each with its own totally different beginning point. If this were the case, then we might wish to ask which of these universes came into being first – which of their beginning points came before the other.
But the times of these two universes are truly two totally separate times, then it would actually be meaningless to ask this question. For there would be no one “Time” in which the events of both of these universes would be arranged, such that we could say which beginning came before the other. Rather, this universe would have its time, in which its own events would be ordered, just as that universe would have its own time, in which its own events would be arranged. But this would be all that we could say. Since there would be no one “Time,” an event in the first universe would have no temporal relation to an event in the second, any more than a body in the space of the first universe would have a spatial relation to a body in the second (since there would be no one “Space” that encompassed them both, and opened up the ground for a spatial relationship between the two.)
Hence, there may be more than one time, just as there may be more than one space, without these times all being part of a single Time, and without these spaces all being parts of a single Space. If this were to be the case, then the word “Time” would have to be understood to refer to our time, just as “Space” would have to refer to our space, and “World” would have to refer to our world.
I can now rephrase the question that I began with:
Whether there is one time, or many times, it is clear that the word “time” means something, and that there is something that a thing must be, in order to be a “time.” My question, then, is – what is that thing? Whether there is one time, or many times, what does it actually mean to be a “time”? Or, put differently – what is the nature, or the essence, of a “time”?
Time is made up of two kinds of parts: lengths of time, and moments.
A length of time is a part of time that can be divided into smaller parts. For instance, a day is a length of time, since it can be divided into hours. Likewise, an hour is a length of time, since it can be divided into minutes. Likewise, a minute, and a second … etc.
By contrast, a moment is a part of time which cannot be divided into parts. By this I mean, there is not one part of the moment that comes first, and another that comes after, but the whole moment takes place all at once, at the moment that it takes place.
A length of time can also be called a “duration,” and a moment can also be called an “instant.”
In our common speech, a “moment” and an “instant” can just mean a very short length of time. Here though, I do not mean that, but rather something that is truly without any parts of any kind – an “instant,” in the sense of “instantaneous.”
Some very great thinkers have claimed that the moment is not a part of time. Their argument goes something like the following:
(1) It is evident that Time as a whole has a certain length, or duration.
(2) Now, that which has length must be divisible.
(3) However, the moment is not divisible. For it has no parts.
(4) Hence, the moment has no length.
(5) But, that which does not have any length cannot be a part of that which does have a length.
(6) Hence, the moment cannot be a part of time.
That is their argument, as I understand it, and why a thinker like Aristotle or Aquinas seems to have believed that the moment was not a part of time. However, in my judgment, this argument is false, and the moment is a part of time.
For, the present is a part of time.
But, the present is a moment.
For, if the present was not a moment, then the present would have to have parts.
But then, if the present had parts, this would either mean that the later part of the present is in the future, or that the earlier part of the present is in the past – both of which are absurd. For it is evident that the future is something separate from the present, and that the present is something separate from the past.
Likewise, if the present had parts, then one part would have to come before the other. But then, this would mean that, when the first part of the present came to be present, the rest of the present would not actually be in the present – which is absurd!
Hence, for both of these reasons, the present does not have parts.
Thus, the present is a moment.
But, the present is a part of time.
Thus, moments are a part of time.
Further, since there have been many present moments, it is also clear that there have been many moments which have been a part of time.
Likewise, the past is wholly composed of moments.
For, the past is every part of time that was once the present.
Thus, every part of the past must have once been the present, either all at once, or part-by-part.
By this I mean: if x was a part of the past, then either x as a whole was once the present (all at once), or else each part of x was once the present – this part as a whole, and then that part as a whole, and then that part – until each of the parts of x had been the present. For otherwise, x could not be a part of the past – for the past is just the totality of times that had once been present. Hence, every part of the past must once have been the present, either all at once, or part-by-part.
But, the present is a moment.
Hence, in order to be the present, a part of time must be a moment.
But, every part of the past must once have been the present, either all at once, or part-by-part (i.e., either the whole part was the present, or else it is divided into smaller parts, each of which was the present.)
Hence, every part of the past must either have been a moment, or else be composed of smaller parts, each of which is a moment.
Thus, the past is wholly composed of moments.
For the exact same reasons, every part of the future will be a moment, or a group of moments.
Thus, the future is wholly composed of moments.
Now, there are three parts to time: past, present and future.
But, the present is a moment.
And, every part of the past was a moment, or a group of moments.
And, every part of the future will be a moment, or a group of moments.
Hence, every part of time is, or was, or will be, a moment, or a group of moments.
Thus, time is wholly composed of moments.
In a geometrical line, the line can be always be divided into smaller lines, but it can never be divided into points. For that reason, among others, the point is not a part of the line, but is only a way of marking off one line from the next, or from the surrounding parts of space.
By contrast, in time, the parts of time are the moments, and the “lengths” are just groups of moments. But there are no “lengths” in time, as things which exist separately from the moments that comprise them, any more than there are “groups” of human beings, which exist separately from the individual human beings themselves.
Thus, the moment is the fundamental part or element of time.
For time is nothing more than a group of moments, arranged in a certain order or sequence.
And the moment is something void and empty, and the world-state is the content of the moment.
That much, then, about what time is, or the nature of time.