Philosophers and physicists have developed conventions for speaking of time, but none of these ever say precisely what time is, or even if it is mind-independent. Space-talk is vague also, but not as vague as time talk. We can conceptualize space as a container in which objects exist in various relations of distance and direction. This may not be a complete physical description, but it describes space’s functional role. The structure of space is controversial, but there isn’t much disagreement about its mind-independent existence. This is not the case with time.
We say that time is a one-dimensional container along which we can place not objects, but events. Events can have various temporal distances from one another, but only one direction; from past through present to future. Once an event is fixed in time, past, no “new event” can be placed at an earlier time. This fixity on one side of the present, contrasted with a converse openness to contingency on the other is a central property of time. But it is because this quality is so ridged, and so universal, that it seems to disappear into the phenomena that occur within it.
In examining this hypothetical container we discover that from the present we can only discern evidence of what came before, in the past. We can project certain regularities into the future, but unlike the past for which records or markers exist in the present, there are no records or markers visible for the future. We also notice that from the viewpoint of our experience it is always “the present”. Unlike space within which we are patently able to move to different locations subjectively (in our experience) and objectively (from the viewpoint of third parties) we are not able to experience, or directly observe, anything other than a present moment in which movement and change is the only constant.
Change always occurs in the present which never moves off the unfolding flux of events. Put another way, where that flux is, is the present. This leads a large coterie of philosophers and physicists to say time isn’t an identifiable property of our universe. The causal net, process, is real, but time is nothing but a mirage in subjective mind, a way to interpret the net’s unfolding. That net is, after all, unfolding as patterns of brain states simultaneous with its evolution everywhere else. Consciousness rests on this same causal link.
Philosophers talk about time in tensed (A-series) and non-tensed (B-series) language, the ‘A’, ‘B’ business made up by a Scottish philosopher named McTaggart back in 1908 who argued that time didn’t exist because all talk about it was circular or inconsistent. “Tensed time” means there is a reference, an index, which is always our own subjective experience now. Events will happen in the future, happen in the present, and having happened are now past. Subjectively there is a “flow of time” from future through present to past. A-series talk focuses on subjectivity; a description of how we sense time.
Tenseless time talk is discrete. Event ‘X’ happens earlier or later or simultaneous with event ‘Y’. When speaking in these terms, it doesn’t matter where we are among the event relations. X can be earlier than Y whether our now succeeds Y or is somewhere between X and Y. If our now precedes both X and Y we can project their temporal relation without indexing it to our present temporal position. B-series talk is objectively focused on temporal relations independent of mind. Neither “A” nor “B” talk commits one to a particular view of time (existing or not) as such.
Most physicists (and philosophers) are either ‘presentists’, ‘eternalists’, or a particular combination of the two. Neither view commits one time’s mind-independent existence. Presentism relies on a certain idea about what “is real”. A real is something that you can “go to”. You can go to Mars, Mars is real. But you cannot go to the past or the future.
Time, whatever else it is, is not something you can “move around in”. only the present is therefore real. Presentism makes unsurprising our plain inability to move around in time. It accounts for our always-in-the present experience, but it remains non-committal about the physical reality of time as distinguishable quality of the universe.
Presentists have no problem talking about the past. There are plenty of markers or records in the present that signal past events. Importantly the events signaled are not occurring now, but their records, evidence of their happening, persist into, and become a part of, our present. That the intervals between past events and their present records seem to be real gives Presentism most of its philosophical trouble.
Marks or records relate time to truth and facts (see “Truth and Truthmaking”). The proposition “Julius Caesar died on March 15, 44 BC” is true because he did in fact die on that day. But is it the fact of his death in the past that makes the proposition true, or is it the record of that death persisting into the present to which the truth is connected? If we had no record of his death today (as is true of so many nameless historical passings) we would not be able to say that any fact (past event or present record) anchored the truth of the proposition.
Yet we also want to say there were events in the past, for which we have no records, whose facticity would make propositions about them true if records of them persisted to the present time. We discover new facts about the past precisely when we discover that certain present “states of affairs” are records of those events.
Facts are immutable. Time is so universal that immutability alone is sufficient to assign the event to the past. Part of what we mean by past is that some “state of affairs” came to be in just the way it did when that time was the present, and by so coming to be, became a fixed actual while before its occurrence it was only potential. Caesar’s murder was contingent, not necessary. It might have been that all the perpetrators and Caesar were present at the time and place, but some other event took place “there and then” that thwarted the planned deed.
Events happened as they did, but might have happened otherwise. Happening fixes their being, their facticity. Once they have happened, they cannot have happened any other way. This “locking into place” of what were, until now, only potentials, fixing events, is one of time’s salient properties.
Presentism’s recognition of records or markers in the present as evidence of events or states of affairs no longer real, must then connect these markers with the events they purportedly represent. It is something of a paradox to say the vibrant life and events of ancient Rome on the day of Caesar’s death, a present undoubtedly real to them at the time, has become unreal in our time while all the same, some part of the events of that day have perdured through the interval between that day and now. That perdurance is, after all, how we come to connect them up, to assert that they are evidence of past events. These markers have remained real, although often changed, in the interval since they came to exist. Such changes as they undergo (for example the gradual degradation of a ruin), have a continuity traceable to a prior present. Does it matter then if we say the past is also real but fixed?
Since unicorns are not real, saying “this unicorn is bigger than that unicorn” makes no sense. An analogous problem exists for Presentism concerning temporal intervals. If the past is not real what does it mean of two past events that one took place one year (or one minute) before the other or that some other event, a war for example, lasted thirty years? Records of these events are all real at the same time, now, but how can two events no longer real have a real interval between them? We can of course say that this record “came to exist” some years before that record, but is such a statement comprehensible if the past is no longer real?
Eternalism asserts that the past, present, and future are real even in and for the present. Eternalism does not commit one to saying that time is real, but rather measuring temporal intervals is never absolute and what looks future to our perspective might be past in another. Eternalism has swayed physics since Einstein’s publication of his theory of Relativity which has some strange and counterintuitive implications for our measurement of time. From within a reference frame (a physical system moving broadly together) time measurement by the speed of light seems identical. But when we look from one frame to another, frames moving faster than our own have slower moving time and vice versa.
This observation means that between frames it is impossible in an absolute sense to say that one event occurred earlier, later, or simultaneously, with another event in a different frame. Fixing a “time line” for events is possible only relative to the observing frame, not over all. Years of experimental work have indeed proved that a clock ticks more slowly in a frame that moves faster (relative to the speed of light) through space than in one that moves slower. Clocks also tick more slowly more deeply in a gravity well. There cannot now be any doubt about these observational results. This has led many philosophers and physicists to conclude there can be no such thing as time in an over-arching sense, only relative times specific to individual frames of reference.
Eternalists do not believe they can “go to” the past or the future in their own frame except for the trick of leaving their frame and going to another where time is slower then returning to the original frame. It would seem as though you have gone to the future (of the frame to which you have returned). In reality, this amounts to waiting out a certain number of clock ticks in the original (temporally faster) frame by spending time in a temporally slower frame.
Eternalism avoids committing itself to the present being in some sense special over-all. Of course it is special to us, and everyone agrees that psychologically it IS special because our subjectivity is limited to it. We are conscious only and always “in the present”. The “reality of the future” in Eternalism is a matter of some faith. It falls out of the mathematics of Relativity, but cannot be experienced observationally other than the trick of “waiting out” another frame’s clock ticks while in a temporally slower frame.
While there are events already past in some other frame that appear to lay in the future of our frame (and vice versa), those events are never observed until their light reaches the observing frame. It is an axiom of our space-time geometry that when the record of an event reaches us through space, our recording temporally succeeds its occurrence. No matter how the “pace of time” varies between any two frames, one frame cannot view an event in any frame before the event happens.
All of these considerations (a much oversimplified sketch) have led many philosophers and physicists to infer there is nothing to time at all, nothing other than a psychological response to motion (and cause) in space. One state of affairs unfolding into another needs some interval and we can assemble that unfolding (within a frame) into a “time line” of “earlier” and “later” states of affairs. Julian Barbour in “The End of Time” (1999) accepts as an axiom of his faith that the future is real and already populated with “states of affairs” presently invisible to us. This leads him to advance a theory in which events of the present not only rest on a past and present foundation but are pulled into their new arrangements by the already settled reality of the future.
For Barbour, time simpliciter is not real, but there is a present everywhere. There is a fixed landscape of future events towards which the present, everywhere, unfolds. His landscape is filled with peaks and valleys the depth of which represent the probability of a given event or state of affairs unfolding in just that way and not another. Barbour does not deny that to us, it appears as though events flow onto this future landscape, but he insists that this is merely appearance, psychological time. Instead, the landscape fixes the distribution of “future states of affairs”.
STANDING NO-TIME ON ITS HEAD
What is it that we suppose time does for us? It allows for motion of course, and therefore cause. To cause requires time. Yet as in Barbour’s theory, we need not, as a result, think that time is a mind-independent property of the universe. In “Time, Tense, and Causation” (1997), Michael Tooley asserts that time is nothing more than a psychological expression of cause. He believes the present and past are real (though not the future) because causal unfolding happened in the past and is happening now, in the present. But like Barbour he believes that time, as such, does not exist. The present is real to experience, and the past is real because events, now fixed, happened, but time is real only to mind.
For Tooley, time is not a property of our universe, but motion and cause are properties of our universe and creatures such as ourselves report this unfolding of the causal web as time. Tooley rejects the physical reality of block time because in his view, the future is not real. There are no events there (yet). But his view does not escape the problem of simultaneity. He concedes that it is not possible, in principle, to place every event in the universe on a single time line. It makes no sense, for example, to say that “the universe is 13.8 billion years old”, something that can only be true (made true by our temporal relation to the big bang) from our specific frame of reference.
In a recent book, “The Order of Time” (2018) Carlo Rovelli more or less agrees with Michael Tooley about causal process, in Rovelli’s description “change and event unfolding” being the real phenomena that manifests in human psychology as a passing of time. Rovelli concedes that this experience is real enough and founded on thermodynamics, but outside of it, there isn’t any time at all, not even a present!
In “The Singular Universe and the Reality of Time” (2014) Roberto Unger and Lee Smolin take the opposite tack. Their claim is that time is not only mind-independently real, but the most fundamental and over-arching property of our universe. Space can literally come and go in cycles of gravitational collapse and big-bang creation. These cycles are possible because time goes backwards and forwards indefinitely.
Precisely because time is the universe’s fundamental property and, as Unger puts it, “drenches everything” it is a property that cannot be isolated, but is implied by its effect: Motion and cause occur in our universe and history is a particular path taken from the big bang to now, through time. The present universe is a combination of all the space-time paths taken in its history. These paths are real from their beginning notwithstanding they are forever fixed behind their leading edges. Time is not a phenomenon in the universe, but rather the environment in which the universe and its properties cohere. Time is real, because it is the stage on which cause, event unfolding, forms our totality.
It is a truism that the physical sciences can only measure phenomena of the physical world. All our instruments, and the means by which instruments report what they detect, are physical! It is a theorem of causal closure that physical phenomena result always and only in physical effects, and that those effects therefore arise from physical phenomena alone. Instruments and the phenomena they measure both conform to the same physical law. It is precisely the nature of measurement to convert or map one phenomenon (form of energy) that we cannot measure directly into another which we can. Laws remain the same, but phenomena become distinguishable because their interaction energy is convertible.
All of these variously converted phenomena are inside the universe. But time is not inside the universe, it is a fundamental quality of the universe. Everything we know, the instruments and the phenomena they measure are drenched with the same time. We can measure intervals of time by counting harmonic oscillations (from orbits of planets to vibration in atoms), but cannot map time the way we map energy conversions because all of those maps occur within a common ocean of time.
Since cause and time are so closely associated does it make any difference to say that time emerges from cause (Tooley) or that cause is possible thanks to time? Functionally, perhaps not, but each view has philosophical consequences. Assuming time is an ocean embedding everything else (including space) allows Unger & Smolin to reject an unverifiable multiverse.
If time is the universal ocean of the physical then our universe and its special properties is the present variation of a succession of universes each of which inherits characteristics from its prior ancestor. Present characteristics are traced from former characteristics through a temporal interval of extreme (but not infinite) pressure and heat (the big bang). This lets Unger & Smolin imagine that characteristics of the ancestral universe might one day be recognisable in this one. The transformation from one universe to another, unlike the multiverse, is hypothetically, a testable hypothesis.
Global time is yet another outcome of the Unger & Smolin thesis. The universe has the same age in every frame because different time measurements, intervals, can be mapped to one another. Clocks in our frame say the universe is 14 billion years old. This might be 10 billion years in a faster (through space) moving frame as measured from our own, and 15 billion in a slower moving frame. Yet from within all frames the recombination event (in our frame 380,000 years after the big bang) occurs at 0.00275% of the temporal distance between the big bang and that frame’s present.
From the viewpoint of any frame then, all the events of the universe can be fit, proportionally speaking, in the same order in every frame! We can, in other words, map our 14 billion years into the measurements in the other frames while keeping the same order of events. In the Unger and Smolin view, it is conceptually possible to place every event in the universe on a single time line. That the universe has a certain “global age” that is the same in all frames becomes meaningful.
THE THEOLOGOCAL VIEW of TIME
Imagine an alternate possible universe that, at first glance, looks much like our own in that all the stars, galaxies, and planets are distributed in space exactly like they are for us in the real world. But in this alternate universe, there is no time and so no change. Everything is static, nothing moves. Of course this isn’t physically possible, a star could not be a star if in stasis. We are imagining here. In our imaginary universe there is no such thing as a light-year because there are no years, or for that matter hours or any other interval of time.
In our universe we can measure distance by time because we know of a phenomenon, light, that never varies in its speed through the vacuum of space. But we cannot do this in the imaginary universe because nothing moves, there is no change. There can be no speed which always involves distance and time. But there can be a concept of miles, or feet, or meters because defining those magnitudes need not involve time.
Now suppose you live in this universe (again, you cannot, but let’s imagine that a subjective view exists and has experience) on the planet Earth. Suppose you have the means to visit another star, say Arcturus. For simplicity let’s call a light-year 6×10^12 miles (it’s a bit fewer than that but I want to keep the math simple). Arcturus is 37 light-years (again the real figure is a bit less) from Sol. That comes out to 2×10^14 miles. In our imaginary universe Arcturus is that distance, in miles, from Sol even though light-years do not exist. But if you had the means to transport your consciousness to Arcturus, you would, in our timeless universe, cross the distance instantaneously. No time can elapse because there is no time. Want to go from Arcturus to Antares? Another instantaneous transition in space. Why stop at stars in our own galaxy? Visit Andromeda or any other galaxy in the universe, all instantly. Notice the jump from Sol to Arcturus to Antares, to any galaxy all, takes place timelessly. No time elapses in the entire multi-jump transaction.
Here is the point of the thought experiment. You could visit every star and galaxy in the universe instantaneously and that amounts to saying “at the same time”. This makes you omnipresent. You can literally be everywhere in space simultaneously. Supposing you could have experiences (yes, real experience demands time, but again we’re imagining) in all of these places. Not only could you visit everywhere simultaneously, you could remain in all places indefinitely! You would have the experience of everything everywhere simultaneously. You would be omniscient. By extirpating time from our universe creatures like ourselves gain two of the three infinite powers normally ascribed only to God.
God being infinite and eternal is “outside time”. Eternity is not merely “endless time” it is, as with my thought experiment above, something entirely different. In the Unger & Smolin view there is no eternity but time does go backwards and forwards indefinitely (not infinitely, leaving a hanging ontological question addressed only by a “God hypothesis”). But the story of a universe created by God, as near as our metaphysics can put it together puts time in exactly this same role. It is the ocean that governs our universe over-all.
We live in a “time governed universe”, meaning exactly what Unger & Smolin mean by time, an over-arching environment in which the objects, processes, and nominal regularities that describe them, are all time-dependent. The mathematics of basic physics works both forwards and backwards in time, but our actual physics, the macrophysics of our universe, does not. God may be “outside time”, but we live in a “time drenched” creation.
Nor should we assume from this theological view that time and eternity are, necessarily, the only two facets of the universe. Besides eternity and time it is possible there are other creations, ontologies that are other-than-eternal, yet not time-bound. But while this is a metaphysical possibility thanks to God’s infinity, there is nothing more we can say about such regimes should they exist. We are stuck in time and cannot detect, that is measure, anything other than time-bound phenomena as Unger & Smolin claim. Even to say “God is eternal” is only a placeholder (We have no sense of what eternity is really like) albeit one made reasonable by the philosophical demands of infinity (see my “Prolegomena to a Future Theology); a causeless, eternal, starting point grounding rational thought.
Yet there is something more here, something ignored by physics and philosophy, for which theology accounts. In both the “time does not exist” and the “time is the ocean” views, we should not expect to be sensitive to time simpliciter. A fish is, presumably, not aware of the ocean in which it swims. How are we aware of time? The philosophical community universally credits our time sense to consciousness in general. Brain processes occur on the leading edge of the causal web with all other process. It makes sense that our experience takes place with time always in the background, and this for animals as well as humans. But for human beings, time is more than background.
Animals live in the present and have memories but these are not connected to abstract ideas of past, present, and future. Human beings not only live in time like the animals but we are abstractly aware of time. Given that everything in the physical universe of our experience is “drenched in global time”, how is it that we are able to distinguish or identify time as a distinct quality of our experience at all?
What theology gives us is personality (see my books and the essay “Why Personality”). Human consciousness is able to distinguish time because human mind amalgamates a changeless pattern. Mind, consciousness is drenched in time and so constantly changing like everything else in the universe, but personality, our agency, remains fixed. Personality provides the contrast (changeless in the presence of otherwise ubiquitous change) by which we distinguish time itself.
Just about every philosopher disagrees with me and insists that personality (agency being merely another affect of consciousness) changes with everything else. All of these thinkers universally fail to distinguish personality from character, personality’s expression in consciousness and behavior. Character changes, but the personality centered in that character does not. This is how I know that I, the same person, persist (or perdure) through all the character and bodily changes I’ve experienced throughout my life. My body changes, my mind changes, my character changes, but I, the person, have not changed. I am the same person experiencing all of these changes throughout my lifetime.
How is it possible that this miracle of changeless pattern exists in a universe in which all else changes in the ocean of time? It exists and can exist because it comes direct from God who is infinite and changeless and is therefore the only possible source of it. Indeed it is the only phenomenon in the universe of our experience created directly by God and is the real meaning of the phrase “in God’s image”, that is, our being personal. All else, all the rest of the finite creation, including life and consciousness, arises indirectly. God remains the ultimate cause of everything, but the physics we experience, including its embedding in time, has come about indirectly, beginning at some fundamental level through a chains of physical cause.
I go into this subject in much more detail in my books and linked essays, but it is worth pointing out here that the higher animals, while conscious and sensitive to environmental clues occurring in time do not separate time from the other dimensions of their experience. Animals experience time in the same way that they experience values (see again the Prolegomena linked above). They are immersed in them (and it), but because animals are not persons they cannot distinguish time (or values) from their unified experience. A lion is not abstractly aware of being the same lion today as she was yesterday. Animal mind, like human mind apart from the personality pattern, changes along with everything else.
Personality may be the changeless benchmark by which we recognize time as such, but theology gives us something else with regard to mind-independent time. It entails the reality of the future! For Unger, Smolin, and Tooley, the future is not real because there are no events there; the causal nexus is, by definition and experience, the present. But theology fixes one event in the future. It is necessary, if there is a God who is God, that the time-universe has some purpose, some end state that must, also necessarily, come about. This would not be the end of time, but rather the achievement of some intended state of affairs in time.
From the principles of God’s infinity and human sensitivity to values, we can infer that this end must ultimately involve goodness, love, between all persons and become the best possible universe! We do not know what the physical state of the universe will be then, nor do we know by what contingent path it will arrive at that state. But that it must arrive eventually is certain and that fixes an event, the achievement of God’s purpose for time, in the future. If that is the case, the future must be real.
Everything in our physical universe, including the physics itself must have a causal beginning. Physicists point to the quantum vacuum, but if Unger & Smolin are right, time itself conditions or constrains this regimen. Physics cannot cause time, rather time is the environment in which physics takes place. But something must then ground time itself, something Unger & Smolin lay aside as brute and un-analyzable. They are correct. Without a “God hypothesis” we cannot make sense of a “beginning of time” even while making sense (the quantum vacuum) of a “beginning of space”.
I am happy with a theological underpinning that makes time real, an ocean that characterizes our universe. Most philosophers and physicists are happy to assume, from our inability to observe any but time-bound phenomena, that time is an illusion arising from motion which underlies cause. It was satisfying to discover a philosopher (Unger) and physicist (Smolin) who are not so flip and recognize that time is the real foundation of our universe. But even, assuming they are correct, to identify time with the over-arching environment within which the system that is our physical universe works, is only a metaphor. It is not to say anything about of what, exactly, time consists.
Time isn’t a substance any more than cause is a substance, but it isn’t a process either. To say it is the foundation on which cause, process, rests is only a metaphor though apt. The exchange of conserved quantities that underlies physical cause is properly a mechanism, and time plays an enabling role. But physical cause is effected by exchange of various conserved quantities and often the transformation of one such quantity into another. By contrast time enables all these uni-vocally. To “exchange conserved qualities”, whether charge, momentum, or energy demands time. Time mediates all of these exchanges, but that is to say nothing more than that they all occur in or through time.
Thanks to time’s global character, physics can safely ignore it. The “time factor” appearing in equations is a stand-in taking duration into account. But as far as concerns physics nothing more needs to be said about “global time”. It is nothing more than a manner of speaking. But if Unger, Smolin, and indeed Theism are correct, such a view, while enough to support calculation, misses an important characteristic of the reality of our physical universe. While it is possible to understand phenomena within the universe without supposing global time is real, it is not possible to understand the universe as a whole. Of course theology enriches this insight, but even without it, Unger & Smolin are, I believe, correct in that we cannot understand the facts of our cosmological history unless time is real.