…People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion. – Einstein
I’ve been troubled for a few years now about the nature of time. It is a question that has prodded me. We necessarily have phenomenological experience of time, when we sit and think, when we go about our day, in times of boredom or joy, but it remains ever furtive and quiet, never placing itself strictly in the mind’s eye. My first worry came when learning about special relativity, though its implications never quite struck me with the vivacity that they ought have. I was only awakened from my dogmatic slumber after reading Augustine’s Confessions, and there I learned that, if nothing else, there is something deeply disquieting about the nature of time that our common sense understanding does not quite grasp.
It seems that what time is is obvious, if not self-evident. It is a kind of river, that flows and I with it. As I pass down the river of time, events that are future become present, and events that are present escape to the past (or is it that the present ever moves forward?). The entire universe is subject to its continually changing force. At one moment I am now. I am typing these words, and this moment is present. Now as I move on to type these proceeding words, that moment is past. At just a moment before it was future. That moment, whatever it contained, of the clicks of the keyboard and the firing of neurons and transistors, is somehow different now than as it was present. All seems well—and yet there is something that troubles me even in this common description. The moment I subject time to analysis, as Augustine points out, I am no longer able to explain what it is, or even what I mean by it.
How can I measure a change in time? With a clock, you might answer, and growing tired of what is obvious. Yes, perhaps. When I measure the change in something, say distance, or viscosity, or temperature, I am referring to a change with respect to time. I can say that a spaceship moved a distance of 500 meters in 1 second. But when we think of time we think of it as changing in itself. That is, the future becomes the present which becomes the past (or some variation thereof). So the question I mean to ask then, is how can I measure the passage of time itself? or, how fast does time flow? If change is necessarily measured temporally, then to describe a change in time itself I must invoke time to describe the change that it experiences. I can say that time moves 1 second in 1 second, but that is tautological, and while true, it is also true that I eat 1 apple for every 1 apple that I eat. There can be no change at all without a change in time itself, for if the moment is eternally present, then nothing is coming into being or coming out of existence—everything simply is. Measuring change, it seems, is necessarily temporal, and so measuring a change in time itself seems to leave us with no way to measure it that isn’t meaningless.
And if I cannot measure the passage of time, then it seems I cannot measure what a moment is. I can say today is the present day. And I can further say that it is the present hour, 11 PM, and more it is the present minute and the present second. But when, exactly, does the present become the past, and the future the present? Is it somewhere in the thinnest slice of its second? If I were to devise a sieve, capable of parcing every part from a second, would I discover what we call the present moment? No matter how thin I slice, there will always be a moment of time yet thinner (or perhaps not, if there is some quantized limit), and so it seems every duration of time will include a moment present, but also a moment past and future as well. Then it seems when I talk about something being present, the rain falling on my roof for example, I cannot even define what I mean by present.
You may say that I am being too picky. We can say, for example, that an elephant is larger than a mouse, even though we have not measured them both down to their every atom. But the states of presentness, pastness, and futurity are different things entirely. I can measure length and be satisfied that the elephant is larger than the mouse by comparison. It is a relational truth dependent upon two observable determinations. And furthermore I can be satisfied on the metric that I used to make the comparison. What is a meter? It is about the length of the standard kept in the vault in Paris, or to get even more precise, it is the distance that light travels in a vacuum in a certain amount of time. But nowhere can I relate the moment of the present to another. A moment is found in no vault; nowhere can I point to an identifiable moment, and say with surety that one moment is not another. If I say that this very moment is present, how can I know that if I cannot even define what the present moment actually is? It would be very much like saying that this apple is A. Well what then is A? If I cannot tell you then how can I hold the truth that the apple is A if it is not a well defined property, distinguishable from properties that are not itself?
There is something odd about time that keeps slipping away from us as we try to ever approach it. No truth must be sacred, and any truth that falters in the face of introspection must be vigilantly attacked, until it bolsters itself through trial or falls as a conspirator. I no longer believe in the passage of time. I mean to say that the properties of past, present, and future, are not things that exist in the world. I believe they are psychological projections of my human mind, a way in which my mind organizes all of sensible experience.
The Eiffel Tower was not real in the year 399 BCE. That is to say, if you were to ask a woman in that time if such a structure existed, she would be speaking falsely if she replied yes. For something to be real, it seems, it must exist now.* If this were not the case, then in the year 2017 I could say that the conscious being of Socrates is real, and in the year 399 BCE, the Eiffel Tower is real as well. In such a world as this the past, present, and future become indistinguishable from one another, because what else is there to separate that which does exist from that did exist or that which will exist? So by definition, the past and future must be unreal, since they do not exist now (if they did exist now then they would be the present). Of course this means that the future and past are nonexistent. Augustine puts it succinctly, “Of these three divisions of time then, how can two, the past and the future, be, when the past no longer is and the future is not yet?” Speaking about the properties of something that does not exist is simply incoherent. A dog that does not exist necessarily has no properties. So if I tried to relate to you the color of this nonexistent dog, and its name, and the tricks that it can do, you would be right to call me mad. Then how can we speak of the properties of becoming and was being, if the future and past do not exist? And further, can something be born from nonexistence? I do not know. But if only nothing can come from nothing, then time could not pass from being future, to present, to past, since the future (which does not exist) would have to become the present (which does exist) and then just as quickly vanish into the past (which does not exist)—thus the passage of time is impossible.
* You may reply that something that is real is something that exists, did exist, or will exist. And so the fact that the past did exist, and the future will exist, makes them real. But I think this is a poor definition of what we mean when we say something is real. If in the past I was married to someone then at that moment the marriage is real. If in the present moment we are divorced, then the marriage is no longer real—it was, but no longer is. And besides the definition of real is not what is important—the existence of these states is what is. And it is simply incoherent to claim that the past and future exist. When we think of the past, we think of a moment of time that did exist, and the future as a moment of time that will exist. Saying that the past and future exist means that there would be no difference between them and the present, making the distinction meaningless. The only other option is to say that the future and past do not exist. But if past and future don’t exist, then only the present does, and there can be no change at all without a change in time itself, for if the moment is eternally present, then nothing is coming into or out of being—everything simply is.
An argument of this form was first presented by Parmenides, the pre-Socratic philosopher. The implication of the argument is that the passage of time is an incoherent idea. The past and future are nothing (they do not exist)—so how could we ever make sense of speaking about them? There are no properties of nothing, no generation of something from it or destruction of something out of it—it simply is not. Then it seems when we speak of the future and past we might as well be speaking of a squared circle or a triangle with four sides. I will admit, the idea that there is no change, that time does not flow, and thus everything exists as a perfect boundless existence, as Parmenides might say, is counter-intuitive, and I could not blame you for thinking it downright irresponsible.
It seems self-evident: the future becomes the present which becomes the past. But as we have just demonstrated, if the temporal properties (that is pastness, presentness, and futurity) are real, then ascribing them to events leads to contradictions, such as Socrates being both alive and not alive. The common response is that Socrates does not contain both of those properties at the same time, that is, that the temporal properties change with time. First he is not alive, then he is alive, then he is not again, all depending on the position of the ever-moving present. Even disregarding the fact that this has not addressed the main concern of the reality of the future and the past in themselves, let us accept it as it is. Imagine an event P, the death of Socrates for example, which occurred in 399 BCE. And let me utter the proposition, “P has occurred.” Obviously this statement is true at the time of this writing, but it is not true at other times. If someone had said “P has occurred” in 430 BCE, they would be speaking falsely. How then can we evaluate the truth of the statement P has occurred? Well, this statement is obviously contingent upon another truth, that is what the present time is. So P has occurred is true when P is a past event in the present time (a present time such as the year 2017). But the present time is ever changing, meaning that “P is a past event in the present time” is true now, but wasn’t always, and so we haven’t given a meaningful answer as to when P has occurred is true. So yet again we have another contingent truth, since the truth of “P is a past event in the present time” is dependent upon what the present is. Then we must now know when P is a past event in the present time is true, and we may say that it is true in the present. Saying P has occurred when it is past in the present in the present is tautological. We can keep qualifying by saying that it will be true in the present again, but nothing will come from it. We are left with an infinite regress. This means I can never truly evaluate the truth of a statement such as “the death of Socrates has occurred” or “the world will end” or “it is raining” with reference only to the propertied of past, present, and future. The only way to generate a meaningful truth from a statement such as P has occurred, is by locating the statement relationally, such as P has occurred is true after 399 BCE. By doing so, however, we are seemingly conceding that the temporal properties are not useful to describe when events actually occur. Using the properties of past, present, and future, never tells us anything meaningful about the world. It seems that anytime we try to describe time as dynamically changing, we end up with nonsense. An argument of this form was first proposed by J. Ellis McTaggart.
But thus far, you may rightfully argue, I’ve done nothing but play with philosopher’s toys, and given you no reason why these pedantic tricks should be believed over your own two eyes. The knowledge of time comes directly to us from our senses—our experience—you might counter. We experience the passage of time much in the same way that we experience a flower. To doubt the existence of time then is very much like doubting the existence of a flower, and really the entire world enduring beyond the self, leading us into a pit of solipsism. So while it is very possible that time does not exist beyond the self, it is as meaningless a point as the world not existing beyond the self, since both are fundamental to our understanding of any possible experience, and must be taken as a presupposition for any further inquiry to occur.
But do we really experience the passage of time? In the first place, since I can only ever directly experience a singular moment, a direct experience of the passage of time, that is the transitive flow of the past, present, and future, is seemingly impossible. What I mean is that, for example, if I see a petal falling from a flower, then at the moment that (C) the petal reaches the earth, the experience of (B) the petal falling in the air is now only a memory, and the experience of (A) the petal being attached to the stem is yet fainter. A direct experience of something must be made in the present (otherwise it is a reflection on a past experience or a prediction of a future one), but A, B, and C all occur at different times, meaning I never actually experience the events as nondiscrete. But, you may retort, as John Locke did, at the moment of C I reflect upon the past experiences of A and B and from this reflection on the train of ideas that flow in my mind I am able to experience the passage of time. This reflection on the passage of experiences is how I get the idea of one moment passing into another, and thus I am able to (although not directly) experience the passage of time (inductively, you might say). But there is a problem in this account. If you were truly a tabula rasa, and I put before you a series of events A, B, and C, you would have no reason to order the events in that particular order a priori. That is, unless you already had the innate ideas of the succession of events, and the passage of one moment into another. Without this your reflection could never reproduce a coherent and meaningful order of events, because C, B, A, and B, A, C, are just as plausible without temporal ideas already being furnished to the mind. What this means is that temporal ideas (such as succession, and duration, and passage) are not something I directly or even indirectly observe in the enduring world beyond the self—they are necessary to my understanding of the world as I recognize it. In other words, they are ideas born from my mind.
Where do these temporal ideas originate from, if not my experience? Immanuel Kant would argue that my idea of time is a form of experience. What this means is that time (and space, etc.) are not things that exist out there in the enduring world. Rather they are innate ideas, organizational principles, a way in which we as human beings impose order on the totality of sensible experience. Time is not found in experience because experience presupposes time. To Kant, reality is itself atemporal. Time does not exist, and it does not pass. Such a conclusion means that reality becomes unknowable. An undrawable veil is placed between the way we experience the world (the phenomenal) and the world in itself (the noumenal). No amount of physical or metaphysical inquiry will allow us to peek behind the veil, to know a truth in that realm, since our way of understanding the world is irreducibly mediated by the forms of experience, of time, space, material substance, causation, etc.
Kant stands in direct opposition to Newton (whom he admired). Newton built his system of natural laws with the assumption of absolute space and time. Space and time are the constructs of God, real things. If all material bodies were drained from the universe, there would still be a space, and time would flow just the same. This means that space and time are not human constructs or simple relations between two relative bodies. They are real, absolute entities in themselves.
Newton’s conception of time stands in direct opposition to Aristotle, who viewed time as a mere abstraction. Aristotelian time does not exist as such, but only as a way of measuring change. Newtonian time, in contrast, exists even if nothing changes. So not only can things be measured relative to clocks, and suns, and seasons, but there is some background substance—an absolute time—that flows equitably and magnanimously. Framed within these veridical entities of absolute space and time, Newton’s theory of motion was perhaps the most successful scientific theory in human history. It disposed with the two thousand years tradition of Aristotelian physics, and for two hundred years after it loomed to explain the entire universe in precise, predictable, mechanical laws—down to the last atom. But just as the grand unification of physics seemed to be inevitable, and all things were to become subject to Newton’s Laws, it was astonishingly toppled in the early twentieth century by Einstein and his Theory of Relativity.
Light is a kind of wave, that is it often exhibits wavelike properties. As such, many physicists of the nineteenth century expected that it must propagate through some medium, like ocean waves, or sound waves do. This permeating and invisible medium was called the luminiferous aether, after the Greek god of light, and it was something that could play the role of Newton’s absolute space. An aether, or something similar to it*, would be necessary to maintain a universe in which absolute concepts (of space, time, and motion), are meaningful. Newton, by positing absolute motion, proposes that a ball at rest is really different than a ball moving with constant velocity.** Not only are two objects in space located relationally, they are located absolutely—to space itself. But as Leibniz had pointed out, what is the observable difference between a universe at rest, and one where every object is moving five meters per second to the right? If the aether could be discovered, then it would lend meaning to such a distinction, and maintain Newton’s theory.
* Of course there are other things in which we could measure spatial location from, other than bodies themselves. One such thing would be the various fields that permeate the universe, for example the electric field. But the difference between the electric field and Newton’s absolute space is that absolute space is fixed and immovable, whereas the electric field fluctuates with a dependency on the bodies. If I am thinking about this correctly then, it would seem that these fields are also relative, since their existence is contingent.
** Imagine a universe in which a single object existed. Simply looking at the object would not tell you if it was in motion or at rest. But Newton believes that there is a real difference, that is, that the object is in motion or at rest with respect to the underlying space itself, the absolute space, even if we cannot detect its motion.
In 1887 Michelson and Morley discovered that the speed of light is constant, regardless of the motion of the source or the observer. This discovery was profound, and goes against our everyday intuition. If I toss a ball inside a moving train, I expect that the ball will travel with the velocity I imparted to it with the addition of the velocity of the train itself. So the speed of light being constant is very much like me throwing a ball on a train and the ball moving the same speed, regardless if the train is at rest, or moving fifty meters per second or a thousand. This discovery seems to undermine the aether theory. If light was a form of disturbance in a medium, we would expect its speed to vary with our motion through this medium. But it simply does not: the speed of light is constant. The Michelson-Morley experiment showed that light could not be used to establish the existence of an absolute space—if there was an aether, it remained undetectable. Einstein explained this result by proposing that light, and the rest of nature, do not care if you are at rest or in motion—when there is a difference, it is only relative. Thus absolute space was no more. Einstein tell us that the laws of nature (including the constancy of the speed of light) are the same for all observers, independent of one’s (constant) motion, meaning there really is no nonrelative difference between a rolling ball and a stationary one. This innocuous statement utterly alters our understanding of time.
To Newton time is absolute, meaning that it flows independent of any event or any change, and equitably for all things within the universe. Time then is something like a metaphysical clock. Where planetary orbits will vary and pendulums will err, time maintains a smooth constancy, perpetually ticking forward the same for all observers. This understanding of time cannot be correct if Einstein is right that the laws of nature are the same for all non-accelerating observers. Imagine you are sitting on a bench, and you are watching me pass by on a train. Then imagine that two lightning strikes, one striking the track a mile behind me (strike A), and one striking the track a mile ahead of me (strike B). You conclude, quite reasonably enough, that the strikes occurred simultaneously, since they were equidistant and reached your eyes at the same time. Myself being on the moving train, I do not agree with your conclusion. Since I am moving toward strike B, it reaches me first, and so I conclude that strike B was the first to land. In other words, strike A occurred in the past of strike B. You may meet me at the platform, and try to explain to me why I am confused in thinking that B occurred before A, when really they occurred at the same time, saying that since I was moving, my perspective of the situation was misled. But you cannot say that I was truly moving. You cannot say that you were the one truly at rest. Neither of our assessments about the events are privileged. Since there is no absolute space, there is no absolute motion, meaning neither of us can be said to be really moving or really at rest.
There is only motion relative to one another. There is no experiment that can be performed to tell us otherwise. In our day to day lives we arbitrarily assign the earth to be at rest, but we know that this is only that, arbitrary. Without any objective, absolute reference frame to delegate such disputes, we must conclude that simultaneity is relative as well. If there is no absolute simultaneity then there can be no absolute time, since what an individual’s “moment” consists of will be uniquely specified. Without an objective reference frame, we are equally justified in saying that our interpretation of the events is correct.
This means that the properties of presentness, and pastness and futurity, are also relative to each observer. To me strike A occurred in the past of strike B. This means that strike B, at the time of strike A, contains contradictory properties of both pastness and presentness (And to a third observer still could contain the property of futurity). An event cannot both be past and present, meaning that these temporal properties cannot be intrinsic to the event itself. This means that there is no real, objective state of past, present, or future that an event contains. Without these real states then, time cannot possibly pass through these properties, since they do not exist in the world or its events.* These states are only meaningful to a subjective observer. Without absolute simultaneity there is no real present moment, meaning there is no all-encompassing now, and what exactly we mean when we say time passes must be subject to scrutiny.
* I suppose that it is possible that time could still flow, but only relative to each observer. But this seems to me to be a much more complicated view than what special relativity implies, namely the block universe, which we will come to soon.
Relativity dispenses with the possibility of a real passage of time, independent of any one observer. But it does not interfere with our ordinary understanding of causality. If event A was caused by event B, it would never be permitted for an observer to witness event B coming before or simultaneous with A, no matter how much you played with reference frames. This means that temporal relations are preserved in relativity. In other words, even though there truly never was a present moment in which Shakespeare wrote Hamlet, it is still the case that first Shakespeare was born, then he wrote Hamlet, then he died. These facts are preserved in the scheme of relativity, even though the temporal properties are given up. So in this sense we must disagree with Parmenides a little bit—there does seem to be something to time. The relations between events do exist. But the temporal properties must be dispensed with. What kind of universe is this? Most philosophers refer to this as the block universe. Imagine the universe as being a block, with three dimensions of space and one of time (you can’t truly imagine it, so just try to imagine a 3-dimensional universe that you are standing outside of). Someone standing outside of this block would be able to see all events that had occurred, are occurring, or ever will occur. Only the point of the block universe is that there is no true difference between occurred, occurring, or will occur. The outside observer would not perceive the special moment that one could label the present. It would only observe all timelessly existing moments. Your birth, storied life, and death would appear, but attributing any directionality or precedence to the events would be entirely arbitrary, just like an astronaut looking down on earth assigning more significance to Houston than Boston. It could carve out different slices of space-time, seeing what observers in various reference frames would label as simultaneous events, but again there is no reason to give this reference frame precedence over any other. If I live in San Francisco it makes sense to label this position in 3-dimensional space as here, and New York as there. But for someone who lives in Vancouver, there here would be there, and there there would be San Francisco. One interpretation is not more real than the other. We can think of time, the fourth dimension, in the same way. My now is just that, my own, and other observers are not constrained to limit their now to mine. To impose my limited perspective on the totality of nature is hubris in the extreme.
Our senses are reliably deceptive. We must remember that the brain does not map the entirety of the world in perfect replication—nor was it intended to. The brain was forged in evolutionary fire; if a belief or organizational method of the mind, such as the passage of time, is conducive to my survival, then natural selection will favor its adoption. An understanding of the true nature of the world in itself is not necessary. Natural selection would have no reason to favor it.
The perception of the passage of time may be a phenomenon similar to the perception of color. Color does not exist out there. It is a way that my mind organizes sensible experience in a meaningful and useful way. No matter the vividness of a flower, we know that the color is not a property of the flower itself. It is a way in which my mind represents that particular form of external stimulus. Animals capable of perceiving color do so because it is useful. Perhaps the color will help them to avoid poisonous substances, or to find mates. Much in the same way, it is useful for animals to organize events spatiotemporally. Right now it is useful for me to perceive my immediate surroundings, namely this computer, these books, and the world outside my window. It is useful for me to plan what I will do when I return to the United States. A year ago it was useful for me to feel apprehensive about my exams. And you may think me hypocritical for not believing in a now or yesterday but having beliefs such as “now I am hungry” and “yesterday I went to teach.” But I think these beliefs are entirely self-consistent, because one is a matter of what is and the other is a matter of what is necessary. If humans did not have the ideas of “now I am hungry” or “tomorrow I must hunt,” then I don’t believe humans would have survived very long. It is simply the case that tensed beliefs are conducive to my survival, but this does not then entail that tensed beliefs reflect reality. It’s simply that a projection of dynamically changing time is indispensable to the type of beings that we are, and so I must represent myself and my actions and my beleifs as occurring now, or tomorrow, or yesterday, even if I don’t believe this representation reflects anything real.
Of course this could all be nonsense. Maybe philosophers should have stopped digging a long time ago and just accepted the prima facie truth of time. It is, after all, almost self-evident. But I don’t think almost self-evident is a good reason to stop searching for truth. And of course some people are resigned to accepting reality as our irreducible perception of it. But to me this seems to defeat the purpose of inquiry. Because, why then, am I seeking truth if it does not exist? The joy and wonder of this peculiar world would be rendered even more inexplicable, not less, if we say the world is merely our representation of it, because it would be near miraculous for such an enduring consensus to be reached if nothing was behind it. Just because we are incapable of perceiving the world beyond the mind’s mediation does not mean it is meaningless, superfluous, or nonexistent. It simply means that our knowledge of some things is stunted, and perhaps it will remain so forever. And I think that’s okay. As I sit here typing, I can’t help but feel amazed at all that is. Contemplating existence, and phenomena, and representation, it’s all pretty amazing.
Thanks to Adrian Bardon, whom I have borrowed much from his A Brief History of the Philosophy of Time. Other relevant books on the subject that you may enjoy are The Time Illusion by John Gribbin, Prolegomena to Any Future Metaphysics by Immanuel Kant (much more digestible than Kant’s Critique of Pure Reason), Confessions by Augustine, and the Oxford Handbook of Philosophy of Time. Of course, my view on time is controversial. Some good books by physicists with opposing views include Time Reborn by Lee Smolin and Now: The Physics of Time by Richard Muller.