Thinking About Time

dog in the nowWe sometimes say that dogs are living in the now. Sometimes we say that of people who live in the moment and don’t think much about the future (or about the consequences). Whether we mean that as a compliment — as we generally do with dogs — or as an oblique implication of shallowness depends on the point we’re making.

There is the tale of the ant and grasshopper; it divides people into workers who plan for the future and players who live in the now. The former, of course, are the social role models the tale holds heroic. The grasshopper is a shifty lay-about, a ne’er do well, a loafer and a moocher, but that’s not the point.[1]

The point is our sense of «now» and of time.

The previous post, Wondering About Wetness, was about whether we sense wetness, but I touched also on whether we sense time. (Which generated some interesting comments.) I’d mentioned then that time was a topic for another time.


Down the rabbit hole we go!

Now is the time for time!

To start, time is a mystery a bit like consciousness in being something we experience every waking moment[2], but don’t understand very well.

Consider the «now». The invisible, constantly moving, razor edged, singularity that separates past from future. It exists for me as I write this; it exists for you as you read this.

The «now» draws a moving line between two realms that appear very different to us. The one, known, unchangeable history; the other, unknowable, changeable future. (Or so it seems. If the universe is fully deterministic, perhaps the future is as fixed as the past.)

From our vantage point in the «now» the future appears less and less predictable the further ahead we look.[3] The weather forecast for tomorrow is usually right (or close enough), but sometimes they still get it wrong. The weather a year from now? About all you can forecast is the season.

For us there seems a clear discontinuity — the «now» — between the past and future realms. This is just one of time’s great puzzles!


Have you got the time?

When we interact with people, we share the «now» together. That’s different from that other great mystery, consciousness. Inside each of us is an «I» that directs our actions and thinks our thoughts. We can’t share the «I» with anyone (at least not so far), but we do easily share the «now» (or at least we seem to — more on this in a bit).

It’s a good thing we can! Imagine how hard life would be if «now» for each of us was very different. It would be hard to have a conversation or even hand something to someone. Everyone would be literally out of sync!

But we have no idea what «now» really is all about, why it exists. We don’t understand why time exists, what it is, or why it runs in one direction. As far as the laws of physics go, there’s no reason things can’t run backwards.

You ask, “Ah, but what about broken eggs and such?” Well, it turns out that the laws of physics have no problem making a broken egg whole. The egg-breaking process works fine in reverse. You do have to apply exactly the right forces in exactly the right directions at exactly the right times, but it is possible.

egg broken

Easy as falling off a wall!

The point: Breaking an egg is easy. Unbreaking one is hard. Very, very hard (but not prohibited).

We think that enormous difference in difficulty may account for why time runs forward. It might even account for why time exists at all.

We think. But we aren’t sure.

There is a view that the enormous difficulty of unbreaking an egg creates an Arrow of Time[4] that points in the direction of breaking eggs. Also of hot things cooling and cold things warming. These things are due to the laws of thermodynamics.

A key player here is entropy, which I’ve written about before. Entropy is basically a measure of the amount of disorder in a (closed) system. Entropy is why thermodynamics is what it is.[5]

Entropy, in a sense, is the Arrow of Time. (One apparent difference: you can use energy to reverse entropy locally.) The natural state for entropy is to increase, and in the closed system that is the universe, it always does.


Time in Minkowski Space.

The thing is, thermodynamics (and entropy) apply to systems with lots of parts. The molecules of air in a room, or of steel in a bolt, comprise systems of unimaginable size. It is the emergent collective behavior of all those parts that give rise to thermodynamics.

Given the link to thermodynamics and entropy[6], is time an emergent collective behavior? Is time a consequence of the universe rather than a fundamental aspect of it? Does time come from reality, or is it a key part of it?

Speaking of cosmology, Minkowsky Space (which Einstein used to describe Special Relativity) treats time as if it was a physical dimension similar to the three we seemingly inhabit. As such, time becomes the “fourth dimension” and movement in time is treated as movement in (4D) space.

xckd-1524An xkcd comic I especially like comments on how we’re forced along that time “dimension” against our will.

And in only one direction. And always at the same (to us) speed.

Time may subjectively speed up or slow down, but no correct clock you ever carry with you will run faster or slower.[7]

So time isn’t really a dimension. We can choose to move back and forth — or not at all — in physical dimensions. There is also that time has a start point, the Big Bang. Where is the start point for any physical dimension?


If we don’t understand time, figuring out «now» is whole other level.

There’s a philosophical version: The universe is 13 billion years old. Why are we here now? The universe is likely to last a trillion years (at least), so why are we here so early? I’m not asking (or rather, you’re not reading) those questions «now».[8]

nowI mean the «now» that separates past and future.

Even if the future was determined, isn’t it weird we’re experiencing reality in serial fashion? It’s like we’re all riding in cars being pulled through a time landscape.

And if chewing on that hasn’t scrambled your egg, what if I told you that the «now» you experience depends on your location and velocity?

Einstein’s Theory of Relativity has an astonishing consequence: There is no such thing as simultaneity. We seem to share simultaneous experiences, but it’s just a local effect. If you’re talking about people on a distant star—or, worse, distant galaxy—the question, “What are they doing right now?” is almost meaningless.

In the math that describes this distance (as well as speed) plays a role. As it happens, at the distance of the Andromeda galaxy, just walking past someone is enough to create differing accounts between you of «now» in that distant galaxy.

We seem to share the «now» but in fact our little cars are all spread out, some ahead, some behind. Nearby cars going along together do share the «now» but that becomes less true as you consider cars farther away. Yet there is a diffuse moving “cloud” «now» that began at the Big Bang and will continue into the distant future.


time-2So there’s time, and there’s the «now», and finally the question of whether humans sense time (which requires defining exactly what we mean by “sense”).

As I pointed out previously, “Cogito ergo sum,” is a thought that occurs serially in time. The concept of “before” applies to the first word relative to the others just as “after” applies to the last word (even “first” and “last” imply time).

The functioning of any machine (or any algorithm, for that matter) is a process in time. Movement is defined as distance over time. All chemical and physical processes occur in time. Our thought process — our “stream of consciousness” — occurs in time.

If you agree we “sense” love and grief, then time should be a shoe-in. If you at least agree we have a sense of balance, then perhaps we sense time as a mental signal from below our self-awareness horizon. Even if you restrict sensing to the five traditional senses, to have those requires time, so all sensation might be said to include time.

Perhaps we are actually as unaware of time as fish are of water. In both cases, we do know when we’re out of it!

“Stay timely my friends!”


grasshopper and ant[1] For the record, in terms of planning about the future, I’ve always identified more with the happy hopper than the industrious crawler. A tragedy of life is that the good do sometimes die young, no matter how industrious or good or careful they are. I’ve known two things a long time: that life can be short, and that when it ends, I want to be able to say I enjoyed as much of it as possible.

[2] Or so I claim.

[3] An interesting question: To what extent does the past become hard to know accurately as you look further back? Any knowledge set describing the past (including your memory) is subject to decay over time plus having to handle an ever-increasing amount of knowledge.

time fly[4] An all-time favorite: “Time flies like an arrow. Fruit flies like a banana.” (Often misattributed to Groucho Marx. It’s believed to come from an early book about computer parsing of natural language.)

[5] That is to say, a law telling us that, not only can we never win but, we can never break even. Just like Las Vegas.

In every energy transaction the universe extracts a small tax to fund its ever-growing supply of entropy. At some point — the heat death — there won’t be enough ordered energy left to pay the tax, and that will be the end of energy transactions, of being able to do work.

[6] The strong link between time and entropy gives us a bit of a puzzle. If entropy always increases, and the universe is fairly ordered now (after 13.7 billion years of increasing entropy), the very early Big Bang universe must have had extremely low entropy. The conundrum is: How is the Big Bang, in any way, a highly ordered state?

atom[7] What the outside world sees about your clock is a whole other matter. Einstein’s Special Relativity and all that. (I wrote about this in detail in my Special Relativity series.)

An interesting thing to ponder is, given the speed at which quarks and electrons move, they must all have their own frames of reference!

[8] Well, obviously you are (and I did), but you know what I mean.

About Wyrd Smythe

The canonical fool on the hill watching the sunset and the rotation of the planet and thinking what he imagines are large thoughts. View all posts by Wyrd Smythe

9 responses to “Thinking About Time

  • Steve Morris

    A very interesting discussion, Wyrd. I’ve been thinking a lot about time recently too, for various reasons, and might put out a blog post myself. Soon.

    I don’t buy into time as an emergent property. Sure, entropy is an emergent property (thermodynamics applies to large collections of things), but time is best understood at the microscopic level, as you describe in part of your discussion. Observing subatomic particles in your mind is a useful thought experiment, I find.

    As for time being a dimension, it seems to be, but not the same kind as space.

    Our inability to explain time in a clear way seems to indicate a rather large hole in scientific understanding. Usually such holes are filled by a new paradigm. We just need to wait for another Einstein to fill that hole. I hope I’m still around when that happens.

    • Wyrd Smythe

      Thanks. I see that from my notifications that, “Soon,” came really soon! 🙂

      “I don’t buy into time as an emergent property.”

      You believe it’s a fundamental property of reality such as space itself is. I’m pretty sure I agree. Spacetime is a thing in itself with properties that arise from its existence. Spatial components share identical properties, and time has other properties, despite having some similarity to the spatial dimensions.

      I find it telling that, often in calculations, t is considered as ct which expresses time as a length. In terms of units, the expression ct is length/secs * secs = length. Thus ct is measured in whatever length units you’re using for x, y, and z. To show that similarity, ct is often written as w.

      Also telling to me is that the invariant interval in 4D (x,y,z,w) space is:

      ds2 = dx2 + dy2 + dz2dw2

      That minus sign accounts for the Lorentz transformations of SR and shows time to be a different animal than x, y, and z.

      And it’s fairly easy to see how thermodynamics arises from the behaviors of particles when there are known, detectable particles involved. We have no idea what time particles might be. If time is quantized, there’s the chronon, the smallest unit of time, but I’m not aware of any “time particle” associated with that.

      So, yeah, I think you’re right to not buy it. 🙂

      “Our inability to explain time in a clear way seems to indicate a rather large hole in scientific understanding.”

      I find it intriguing that some of our most basic experiences are so mysterious! Time and consciousness are as common as salt, universally experienced, and we really… just… don’t… know! It might turn out it just is, that time is axiomatic, a given.

      The thing about existence is that something about it has to be axiomatic. The Big Bang happened in some context, and maybe that context happened in it’s own meta-context, and so forth, but it can’t be turtles all the way down. At some point, something just is. It’s also true of God-created universes; God just is.

      So maybe time is just part of the fabric and all we can do is observe it and measure it, but we’ll never have a better explanation than that it just is. Like space.

      “Usually such holes are filled by a new paradigm.”

      Could be. As you say, I’d really like to be around to see some major advance in our understanding of reality. Something new in particle physics would be a real treat. My interest in quantum physics pre-dates quarks, so I got to see that one. Finding the Top was as cool as finding the Higgs, but nothing about that was new. Seems the best hope there might be supersymmetry, either confirming or disproving.

      I think I’ve mentioned that, when it comes to GR vs QFT, I want QFT to be the “epicycles” one. I want Einstein’s smooth space and time (I’m fine with matter and energy being quantized). QFT is so weird that it’s always had a tinge of epicycles to me. But if quantum gravity is a true thing, then fine. Either way, it’s another mystery I wish I could see solved.

      Also: a sequel to Prometheus in my lifetime, please.

      • Steve Morris

        You are of course completely correct about the significance of dimensionless time. What I find intriguing about relativity is the seeming importance of speed as the fundamental quantity that affects an object’s mass and its experience of time and space. Why speed? Why should motion be the fundamental thing?

        Do you see what I’m getting at here? I feel that it’s part of the riddle, and that we already have all the clues. The answer is staring us in the face and we just can’t see it.

        You are familiar with Kaluza–Klein theory, I take it?

      • Wyrd Smythe

        Yeah, it’s an interesting question. The mass part I kind of get, because your rest mass is invariant. The increase from motion creates “kinetic” mass. There’s a well-known push-pull equation with guns, for example. A heavy bullet at a slow speed can equal a light bullet at fast speed. You can trade mass for speed (or vice-versa). So the mass part I get.

        The time and space parts are messed up. Just weird. And keep in mind it’s not just motion, gravity (that is: mass) plays a similar role. (I was just reading about how the tensor equations of GR allow you to derive all SR’s effects without the equations of SR.)

        Of course, mass and energy are two sides of the same coin, so gravity is really due to energy. And motion involves kinetic energy (and it turns out you don’t even need SR anyway), so maybe it’s all really about energy. [shrug]

        I’ve mostly run into Kaluza–Klein with regard to compactification of extra dimensions in string theory. I take it you’re referring to the classical 5D gravity theory? I may have encountered it in passing with regard to GR, but all I can say is it seemed to ring a distant bell when I looked at the Wiki page just now.

  • SelfAwarePatterns

    Fascinating post Wyrd!

    I don’t have any well thought out views on the ontology vs emergence of time, but I would note that our “sense” of time is somewhat illusory. Consciousness is often fragmentary and choppy which we’re often not…conscious of. It’s like the hole in our eyes that we never perceive, our brain just works around it. It’s one of the reasons why our only way to measure time is in relation to steadily repeatable natural events (such as the sun rising, moon’s phases, cycling of constellations, etc).

    People often say that it’s meaningless to talk about what’s happening “right now” around, say, Proxima Centauri. I understand the relativity of simultaneity, but it seems excessive to me to say we can’t effectively talk about a common now given that, in relation to us, anything around Proxima Centauri would be moving no more than 100 km/s, less than 0.034% c. We might only be able to calculate the concurrency of events years later, but effectively, there would still be a concurrency. There would be some relativity effects, but not much more than what GPS satellites currently deal with. (Unless I’m totally missing something. 🙂 )

    • Wyrd Smythe

      “Consciousness is often fragmentary and choppy which we’re often not…conscious of.”

      Yes, you’re right, our psychological experience of time is distorted, but as you point out, so is our vision. Cameras capture images better than our eyes, clocks capture time better than our senses. Sadly, most of our senses are, in some way, illusions.

      “People often say that it’s meaningless to talk about what’s happening ‘right now’ around, say, Proxima Centauri.”

      You’re right that after the fact it’s possible to reconcile clocks and see that in a given frame of reference two events happened at the same time. At the same time, in other frames of reference they truly did not. But none of this is available in the «now», only after the fact.

      One thing about Proxima Centauri is that it’s way too close. Its motion relative to us is small enough to basically put us in the same frame of reference. And it’s close enough that it takes a fair bit of speed to really skew simultaneity.

      But another galaxy is another matter. Remember from my SR series how the line of simultaneity is at an ever larger angle as speed increases (reaching 45° at c)? In two dimensions, it’s a surface of simultaneity, and in three it’s a hyper-surface of simultaneity. In all cases, it “rotates” (for lack of a better word) what is simultaneous outside your frame of reference as your speed increases.

      That rotation is centered on you. Only at your position does the simultaneity of the “rest” frame match your “moving” frame. The further away from your position, the more there’s a mismatch.

      The surface of simultaneity always rotates with movement, even slow movement. But its effects are undetectable. Unless you far enough away for the tiny, tiny, tiny rotation to have some effect. At galactic distances, walking speed matters!

      So, for example, while a whole group of stars moving along together in Andromeda might share a frame of reference, for you at walking speed, they totally don’t! (They don’t anyway due to inter- and intra-galactic movement. Your walking just shifts things so you have a personal view of simultaneity there.)

      Cool, huh? 😄

      • SelfAwarePatterns

        It is cool, and I understand what you’re getting at. I don’t think Andromeda is far enough for it to skew too much though. It’s radial velocity is only 300km/s (toward us!). But as you move further away in the cosmos, the relative speed from the metric expansion of space definitely adds up (~70 km/s/mpc). At two billion light years, the galaxies are moving away from us at 15% c!

      • Wyrd Smythe

        Of course, it could be my memory, which is famously like Swiss cheese, but I thought the example used did involve the Andromeda galaxy. Keep in mind the point is the distance, not the relative speed. Even if, somehow, Andromeda and Sol had no relative speed, the distance would make walking here skew simultaneity there.

        Look at it this way: From here the whole of Andromeda covers about 1-2 degrees of sky (depending on what you consider the galaxy). Here’s a good comparison to the moon, which is 0.5 degrees of sky. If you point to any star system in Andromeda consider how small a change in angle points to the next star system. How small is the angle, from here, between separate towns on a planet in a star system in Andromeda?

        I’ll try to figure out or find the math, but my understanding is that walking speed rotates your hyper-surface of simultaneity enough to put those towns out of sync from your perspective. (Of course, it’ll take 2.5 million years for that information to get here, so this is all a bit of a lark.)

      • SelfAwarePatterns

        LOLS! I almost said the same thing about the two billion light year example. It’s so far away that, even if we were immortal, simultaneity between us and them isn’t likely to ever be an issue.

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