Got Time?

For the last week or so, on a physics blog I follow, I’ve been part of a debate about the nature of time. It’s been interesting and fun, but the conversation has reached that point where folks are mainly maintaining their positions, and it seems that the matter has stalled.

Some of the on-going assertions bemused me so much, that I was about to tender one more rebuttal comment… When I remembered what a wiser person, “back in the day” (before the web), said about online debates: State your view. Support it further if you need to address points raised. But once you’ve covered it well enough, just stop. After that, you’re just wasting your time; it’s rare that anyone changes their mind on the internet. Including yours.

Fair enough. I can natter on about it to myself on my own blog, though…

And that’s all this is — me over in my corner muttering to myself about someone being wrong on the internet. Again. But at least I can info dump here and get it out of my system.

Since this is out of sight of those in the debate, I’m just going to ramble about some ideas expressed within that debate. I’ve heard those ideas elsewhere, they’re not new, so this goes beyond any participant, and I’m not pointing any fingers.

It should go without saying this is all just my own opinion. No one currently really knows what time is or why it flows in only one direction. We don’t know if it’s continuous or if there is some (very short!) minimum time — a time quantum (a chronon).

The debate revolved mainly around the question of whether time is fundamental or not. The trigger was a blog post of an email interview with theoretical physicist, Carlo Rovelli, about time.

As it turned out, the interview didn’t really go anywhere, but the comment section got lively. People put forth a number of their own theories about time, some that struck me as… probably not likely.

Keying off those basic ideas, my own ideas (caveat emptor):

Time is unordered.

Most of these ideas propose to show something is “wrong” with time, therefore it can’t be fundamental (or in some cases, even real). The seeds were planted by Rovelli speaking several times about time being more complicated that our experience shows. From the interview, it’s not clear how far he meant that.

One such view holds that, because of how relativity screws up time — simultaneity is strictly local — there is no ordering to events, thus our sense of any “timeline” is an illusion.

But causality orders time. No event can precede its cause. That’s the timeline.

That we can’t untangle the plate of spaghetti doesn’t mean the universe can’t.

It’s like orbits. We can’t calculate a bunch of them accurately, but the universe does it all the time.

That said, between Special Relativity (SR) and General Relativity (GR), that plate of spaghetti is seriously tangled.

Under GR, clocks run slower in higher gravity (from the perspective of those outside — those local to the clock see outsiders’ clocks running fast).

That means the center of the Earth is younger than its surface. The center of Jupiter is even younger than its surface, and the center of the Sun is younger still than the Sun’s surface.

And under SR, things moving relative to each other have different clocks, so the fabric of time is as complex and tangled as smoke in air.

But nature (or physics, whatever) keeps it all straight just like the orbits of planets. Causality trumps all! Light cones never lie!

Time emerges from change.

Another approach holds that time emerges from something more fundamental. One view seems to be that time somehow emerges from change.

I don’t understand how this is possible. We define “change” as two states separated by time. First, one thing is true, then, something else is true. You can’t discuss change except in the context of time.

Rovelli, illustrating how time is more than what we perceive, mentioned how we perceive the Earth’s surface as flat, but from a distance it appears round. (And, obviously, the longer view is the “more correct” one.)

This idea morphed into the idea that such a change is perspective is a change that can occur without time, which supposedly demonstrates that change can be more fundamental than time.

I don’t see any coherence to the idea; it’s doubly incorrect in my view.

Firstly, an abstract change of perspective is not at all the same sort of change we mean when we speak of change in physics.

Secondly, even an abstract change requires first one state, then another state. There is always an ordering of states in time. We can reverse the order to obtain a different effect, thus demonstrating the fundamental nature of time when it comes to change.

Not the other way round. A property can’t arise from something that is necessary to its definition.

time = change

To the extent anyone in the debate actually claimed that time and change were synonymous (which I’m not sure anyone actually did), that’s clearly false.

Change is defined in the context of time, but its description involves more than just time. A system in one state at time changes to another state at a later time. The definition requires two points in time and two states for the system.

A more complicated, less fundamental, concept than time.

Lab results show problems with SR.

Or so it was claimed.

I’m sure this is a misunderstanding. If it were true, it would be huge news. SR is one of science’s most rigorously — and successfully — tested theories. Any violation of it would rock science.

(Like faster than light neutrinos. Which were also totally not true.)

In fact, I read recently that astronomers had an opportunity to track a Milky Way core star as it whipped around the putative Black Hole at the center. Because of the star’s close passing distance, as well as its speed, it provided a test of both GR and SR in an extreme domain.

Einstein won again. Spectra dead on per theory.

So I’m very dubious about claims there are problems with SR.

Time dilation is a mathematical artifact.

It’s not clear if the person making this argument (who is also the interviewer) really means time dilation doesn’t happen, or if it does but is explained in some other way. (I asked; wasn’t answered.)

The reality of time dilation has been well-explored, and it definitely really does happen. Not only in the lab, either. Muons created in cosmic ray collisions with the upper atmosphere reach the Earth’s surface because they are traveling so fast. (If they weren’t, they’d decay much faster.)

It further appears there is a misunderstanding here, too. The idea that time dilation isn’t real is apparently due to early thinking by Lorentz, but that was pre-Einstein. Later Lorentz clearly agreed time dilation is real.

So I’m not sure what’s going on there.


As a closing thought, I have at least one data point suggesting I can be wrong on the internet and be corrected. (I’d like to think it isn’t unusual, actually.)

Over on a SF blog I mentioned my belief that FTL radio might be possible under certain special circumstances (i.e. matched frames). Someone who knew better than I corrected me, and provided an example that made clear what I hadn’t seen before.

And, nope, sorry, no FTL Radio. (Gonna have to write a followup post now!)

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

14 responses to “Got Time?

  • rung2diotimasladder

    This business with GPS and clocks is utterly, utterly baffling to me. In the interview, this part struck me:

    “TH: I agree that common sense can be a faulty guide to the nature of reality but isn’t there also a risk of unmooring ourselves from empiricism when we allow largely mathematical arguments to dictate our views on the nature of reality?

    CR: It is not “largely mathematical arguments” that tell us that our common sense idea of time is wrong. It is simple brute facts. Just separate two accurate clocks and bring them back together and this shows that our intuition about time is wrong. When the GPS global positioning system was first mounted, some people doubted the “delicate mathematical arguments” indicating that time on the GPS satellites runs faster than at sea level: the result was that the GPS did not work [when it was first set up]. A brute fact. We have direct facts of evidence against the common-sense notion of time.”

    First of all, I thought that the interviewer asked a good question, many good questions throughout, actually. But CR’s responses were unimpressive, sometimes even dogmatic. In the quote, I see no “simple brute facts” that tells us our common sense idea of time is wrong. I see instead the suppositions underlying the experiment: that time itself is measurable, and that it’s measurable by a clock. I realize a scientific definition of time is basically, ‘it’s what the (super duper accurate) clock says,’ but this is still a supposition, and it should be acknowledged as such…not necessarily in ordinary uncontroversial science, but when theorizing about the nature of time itself, especially when making controversial claims about its fundamental nature.

    But is time itself measurable by a super duper accurate clock?

    Or is a clock a means of imposing order and objectivity onto time? This is how I see it, thanks in large part to Kant, although even without Kantian philosophy I would think of ‘clock’ time as something different from time itself. (Full disclosure: clock time is my enemy, so there may be some anti-clock bias going on here.)

    Anyway, CR likens a clock to a telescope and says they are both instruments, but he misses a crucial difference–time is, strictly speaking, invisible, whereas objects viewed through the telescope are not.

    Okay, enough about him.

    “One such view holds that, because of how relativity screws up time — simultaneity is strictly local — there is no ordering to events, thus our sense of any “timeline” is an illusion.”

    Yeah, I’m not following. I can’t see how someone could say our sense of a timeline is an illusion…don’t they have to presuppose a timeline of some sort in order to say events are not ordered? Or is the ‘illusion’ of a timeline the foundation on which they’re making this claim?

    “That we can’t untangle the plate of spaghetti doesn’t mean the universe can’t.”

    Indeed. And I think the spaghetti metaphor works well here.

    And good point about causality.

    Obviously I agree that time is not change, nor does it emerge from change. It’s hard enough to consider what timelessness really means…do we need to complicate matters by explaining how time can “emerge” in a timeless, pre-existing change? Can there be a timeless change? I have an easier time imagining square circles.

    As for dilation, sorry, I don’t know anything about it.

    • Wyrd Smythe

      This business with GPS and clocks is utterly, utterly baffling to me.

      In the not understanding the applied science sense, or in not understanding how people are using it in their arguments sense? I can easily help with the former, but may be as puzzled as you about why people think it matters.

      (One thing about that blog, it’s by a working theoretical physicist and written for other physicists or amateurs (like me) who take it very seriously and have been reading about it for many years. So certain background knowledge is assumed.)

      ((In case you do mean the scientific background, I’ll post a second reply with some details.))

      But CR’s responses were unimpressive, sometimes even dogmatic.

      I noticed that, too; he didn’t seem terribly into the interview. It’s possible he was put off by TH inserting what turns out to be his own theories into the interview. (I’m sure you didn’t bother with the long comment thread, but it’s starting to look like TH may have some untenable theories. A commenter, named Amos, has been debunking his views.)

      I see instead the suppositions underlying the experiment: that time itself is measurable, and that it’s measurable by a clock.

      And you’re hardly the first to raise such issues!

      I realize a scientific definition of time is basically, ‘it’s what the (super duper accurate) clock says,’ but this is still a supposition, and it should be acknowledged as such…

      Within serious work, it is. At least on a scientific premises level. I do sometimes think they could benefit from philosophical rigor in examining their assumptions, but generally speaking serious work is pretty good at explaining what’s assumed.

      I’m not sure the scientific definition of time is based on clocks, although it really depends on what we mean. And time is a scientific mystery on some levels, so some of this does get downright meta.

      On one hand, science tends to treat time as pretty fundamental and has no definition for it other than “it exists.” (At some point, it’s turtles, and time is generally thought of as a turtle.) It’s taken as part of the background, like space. We’ve explored its properties a lot, and we have a lot of understanding about how it behaves.

      It’s really hard to define (rather than just describe) something fundamental. Kant’s whole take on it being an intuition, not a concept, is dead on here.

      When you ask:

      But is time itself measurable by a super duper accurate clock?

      That’s more clear. Yes… for the most part. Our clocks have gotten so good they can detect the time warping of a mere 20 miles per hour difference or mere meters in height. Our clocks today are very good.

      We’re certainly measuring something with incredible precision, and it’s a something with consistent properties that strictly obey certain laws.

      Now, clocks are always based on something physical (for an inclusive definition of physical that includes, for example, light). Long ago, drips of water or burning candles. Pendulums came along fairly early. Mechanical clocks have an escapement mechanism, electronic watches use a vibrating quartz crystal.

      The “second” is currently defined as a certain number (9,192,631,770) of a specific type of vibration of a cesium atom in a specific configuration. All other time units are based on the second. (The meter is currently defined by light speed and time!)

      In all cases, some regular behavior of physical reality “keeps time.”

      Is this, per your question, the same as “measuring” time? I think I would call it that. Might depend on your perspective.

      Or is a clock a means of imposing order and objectivity onto time?

      At a human level, perhaps, but I don’t see it that way on a physics level. (Kant came about 100 years before Einstein, and our view of time really changed due to Ol’ Al. I really like Kant’s way of looking at it, but as you said a while back, a scientific view may have to co-exist with a philosophical one.)

      Is a ruler a way of imposing order and objectivity onto space? Well, in a way, sure. If you want to use the space. (Likewise, use the time.) But (as a realist), I would say that objective order was already there, the ruler just measures it and allows me to label parts of it for use.

      I would think of ‘clock’ time as something different from time itself.

      Perhaps in the same way the ruler isn’t the space. The map isn’t the territory. And maybe you’re right. That’s all our clocks are is maps.

      CR likens a clock to a telescope and says they are both instruments,

      Not an ideal analogy, but how about a Geiger counter? That measures radiation, which is invisible. We might even consider a radio, which picks up invisible radio waves.

      Yeah, I’m not following. I can’t see how someone could say our sense of a timeline is an illusion…don’t they have to presuppose a timeline of some sort in order to say events are not ordered?

      Again, I’m not clear whether it’s the logic or the science you’re not following, but I’m getting the impression you mean the logic. Your conclusion certainly seems on point.

      It is, if I do follow them, even the appearance of a timeline that is questioned. That, from one perspective, “B” follows “A”, but from another, “A” follows “B” (and from yet another, they are simultaneous) apparently is taken as evidence there is no ordering to time.

      But causality always applies from all perspectives. No one can disagree on the order if “A” causes “B”! To me, this is clear evidence that time is ordered.

      As for dilation, sorry, I don’t know anything about it.

      Okay, so at the risk of being boring, I’ll tender another comment going (briefly, I promise) into some of the science here. The time dilation is related somewhat to the simultaneity thing.

      • rung2diotimasladder

        I guess the GPS-clock-time issue is baffling to me in both the applied science sense and in how people are using it in their arguments sense. The idea that the clocks would be different is baffling, shocking really. Not because I would expect time to be

        “I’m not sure the scientific definition of time is based on clocks, although it really depends on what we mean.”

        I got that idea from this, which is probably not the best source, but hey, you gotta start somewhere:

        https://en.wikipedia.org/wiki/Time_in_physics#Conceptions_of_time

        “Again, I’m not clear whether it’s the logic or the science you’re not following, but I’m getting the impression you mean the logic. Your conclusion certainly seems on point.”

        You’re right, I was talking about the logic.

        I think I get perspective and that there’s no absolute standpoint. But it’s the clock aspect to this that’s really astonishing. I mean, normally when clocks go out of sync, we assume something’s wrong with the clock!

      • rung2diotimasladder

        Whoops! Sorry about this comment. Something got screwed up, obviously. 🙂

        Unfortunately, I have no idea where I was going with that incomplete sentence.

      • Wyrd Smythe

        So I’ll never know what you would expect time to be!

        (Nice to know I’m not the only one with thoughts that go wandering off never to be seen again.)

      • Wyrd Smythe

        I mean, normally when clocks go out of sync, we assume something’s wrong with the clock!

        Heh, yes, quite true. In this case, not only are the clocks working correctly, but they are, indeed, keeping perfect time. It just doesn’t agree with other clocks that are also keeping perfect time.

        I just read an article about teaching Special Relativity to students learning physics, and it turns out certain mental blocks are well-documented. One of the biggest is how hard it is to let go of the notion of simultaneous time.

        We can make a phone call to someone across the country (or world) and our real-time conversation makes it clear both parties experience the world simultaneously (as far as we’re able to tell). We can even mentally compensate for a time delay due to distance.

        But this notion is actually false, even in our daily experience (but the difference is too small to measure). When you drive to, or from, your house, the clocks in your car run ever so slightly slower than your clocks resting at home. (We do have clocks accurate enough to measure this now, but it would take billions or trillions of years of driving to amount to a second’s difference.)

        So it’s one of those places in physics where nothing in our daily experience gives us any hint of what’s actually going on. Every experience we have tells us everything happens according to some master timeline.

        The article you linked to puts it very well when it says we learned there isn’t a time line, there are only world lines. There is only the “proper” time each clock (“our” clock) measures as it moves through spacetime. And (a big point for me) proper time is always the same. Our clock always runs at the same rate.

        Which (I think) is why people might think it’s subjective or emergent and, perhaps, therefore not fundamental.

        And it does require a counter-argument providing how something fundamental can be relative to observers. How does something fundamental look one way to me, but another to you?

        Unfortunately, the counter-argument is technical enough to, perhaps, not go down well. It’s the combination of space and time, the interval, that’s the same for all observers. That is fundamental.

        (This is what I’m referring to with my quip: “Light cones don’t lie.” 🙂 )

      • rung2diotimasladder

        It does help that the clock’s time differences are tiny. But then again, a small difference is still a difference. And how do we know the clocks are working correctly? Because they resume operating at the same rate after the experiment, in the same environment (in other words, the go back to being coordinated with each other)? Is this outcome true for different sorts of clocks besides atomic ones? What if something bizarre is happening with casium atoms? Why SHOULD the clocks have different readings?

        I guess I wouldn’t have such a problem with this if it were just mathematical. The hurdles that most people have are probably different from mine since I don’t see time as something that’s necessarily objective. It’s the clock-to-time connection…something in there rubs me wrong. The damned clocks!

        Ah, well. Maybe this would make more sense if I could understand the math.

        Well, I just spent the day watching the Kavanaugh “trial” and I’ve reached the limit of my capacity for dueling perspectives. And locally, it’s non-stop TV ads of Kyrsten Sinema and Martha McSally bashing each other. I’m clocking out…ho ho ho…hahaha.

      • Wyrd Smythe

        And how do we know the clocks are working correctly?

        An important question! The short answer is that their behavior matches theory, both in terms of how the clocks work and in terms of how they measure time.

        For example, the relevant vibration of a cesium atom is predicted by theory, and confirmed by experiment. Likewise the behavior of light — another useful clock — was predicted by Maxwell’s theory and later confirmed by experiment.

        SR, which ultimately is just geometry (and simple geometry at that), makes certain predictions about time and space — results that are required geometrically. Experiments confirm those predictions. (In fact, Relativity is one of the two most well-tested — and always successful so far — theories in all of science.)

        The important point is that time’s behavior between clocks in motion with respect to each other is geometrically necessary.

        It’s a little bit like a discussion we had long ago where you mentioned how the imaginary unit (i, square root of -1) seemed weird and artificial (which might well be a constructivist view).

        The thing about i, though, is that it turns out to be necessary to enable a basic property of certain equations: that they all have one or more “roots” (a value for “x” that makes the equation equal zero). For example, the equation x2 - 4 has two roots: +2 and -2.

        But what about x2 + 4? The only way for that to have a root is by “discovering” (or inventing) i. Because then you have the roots: +2i and -2i.

        The business with clocks and length in SR is equally necessary.

        Here’s an example that might help (or not):

        Hold a ruler out at arm’s length such that you’re seeing it square on — you’re seeing the full length of the ruler. Now turn it a bit so one end comes closer to you while the other gets further. Even though the ruler is the same length, it looks shorter, because it’s foreshortened.

        Objects in motion (relative to you) foreshorten exactly like the ruler because they’re turned in time. The leading half is (from your point of view) progressively shifted “away” (back) in time, so it arrives later. The trailing half is progressively (i.e. along its length) shifted “closer” (forward) in time, so it arrives sooner.

        With the front end arriving late, and the back end arriving early, the whole is shortened along its length. And it’s all just geometry.

        Because they resume operating at the same rate after the experiment, in the same environment (in other words, the go back to being coordinated with each other)?

        Yes, with the caveat that while the clocks now run at the same rate, they would show different times because they took different (geometrical!) paths through spacetime. If you reset them to the same time, they would run in sync.

        This is the essence of the “twins paradox” — where one twin flies off at high speed and returns to find themself younger than their stay-at-home sibling.

        Is this outcome true for different sorts of clocks besides atomic ones? What if something bizarre is happening with casium atoms?

        This is a fundamental property of spacetime, so it affects all clocks. And people, as in the twins paradox. It’s well-documented in a variety of domains. (GPS wouldn’t work without compensating for it.)

        This, perhaps, ties back to my discomfort with the idea that “time is what clocks measure” because all this SR and GR stuff happens at the “fabric of spacetime” level, and the clocks just let us measure it.

        Why SHOULD the clocks have different readings?

        It really is simple geometry combined with two crucial axioms: (1) Physics works the same in all frames of reference. (2) The speed of light (actually, of causality) is the same to all observers in all frames.

        The second one can also be stated as: The spacetime interval is the same for all observers.

        The time dilation and length foreshortening are necessary consequences of the four-dimensional (3D+time) geometry of spacetime.

        If you want to re-visit the series on SR I wrote back in 2015, these two posts touch on this aspect of things.

        Twins Paradox: SR #21: Paradox Resolved

        Time Dilation: SR #22: Relative Time and SR #23: Light Clocks.

      • Wyrd Smythe

        Yeah, I was watching the Kavanaugh hearing all day and then the news coverage much of the evening. Very depressing what our culture has sunk to. I remember the South Park episode where James Cameron dives down into the Marianas Trench seeking the low, low, low cultural bar. And that episode was many years ago. That bar has now sunk deep into the Earth and out of sight.

        I think we’re watching the beginning of the end of the human race (if we don’t wake the fuck up). We seem to have peaked and are now sliding back into science- and logic-rejecting Medieval thinking. Tribalism is animalism; the dialectic is dead, weep for our species.

        Good riddance. Humanity never amounted to much that I saw… damn “crab bucket” mentality.

      • Wyrd Smythe

        I get so long-winded I thought I’d split replies by topic. Easier to read and pick what to pursue or drop, maybe?

        I got that idea from this, which is probably not the best source,…

        It’s a fine source! And it does start off, “Time in physics is defined by its measurement: time is what a clock reads.” (Which is sourced from Process instruments and controls handbook, which may not be the best source for a definition of time itself.)

        But I think it depends on what you mean.

        All clocks are based on something physical that cycles at a steady rate, and the second is defined in terms of a clock made from a cesium atom, so in some sense that opening line is the only “definition” we have.

        And I quote “definition” because I think of it as more of a “description.” To me any clock is just a ruler that measures something. (Something fundamental and real.) To me, defining time as what a clock measures is like defining space as what my yardstick measures.

        Which is exactly what some do. Leibniz viewed time and space as relative and existing only in terms of relations, which amounts to the same thinking.

        (Our biggest problem here is that no one really knows what time or space actually are, so we’re all just guessing. We’re deep into IMO territory here.)

        Another might be that clocks and yardsticks measure arbitrary things; the length of the king’s foot, or “X” many vibrations of an atom. The “day” and “year” are orbital coincidences. There doesn’t seem to be any obvious fundamental time or space unit.

        (To the extent there is, Planck length and Planck time, they are so small as to be beyond our technology for the foreseeable future. And may even be mere technology limits rather than fundamental universal ones.)

        So, bottom line, “time is what clocks measure” is correct enough, but (IMO) can miss the point if time is more fundamental. And it may be that, to me, it hints at clocks being the source of time.

      • sean samis

        rung2diotimasladder

        I guess I wouldn’t have such a problem with this if it were just mathematical.

        Yeah; but it’s not just mathematical; it’s physical; it’s how the world really works. Quite counter-intuitive.

        The hurdles that most people have are probably different from mine since I don’t see time as something that’s necessarily objective.

        Perhaps this is evidence that you need see time as necessarily objective. It’s a real thing that defies our intuition.

        sean s.

  • Wyrd Smythe

    Just some basics about how Albert Einstein completely changed our view of time:

    Special Relativity (SR) tied time and space into spacetime — three dimensions of space, one of time. It seemed to make time into something very much like a physical dimension. (And yet there are pronounced differences, as well. We choose to move in space; we’re helpless about time.)

    SR resulted in some weird new truths with regard to time:

    Someone (or something) moving, from your perspective, has a slower clock (time dilation). This is not an illusion, their clock really runs slower according to you. Those last three words are crucial, because, from their perspective, time is just fine, and it’s your clock that’s slow (because they claim to be standing still, and it’s you that’s moving).

    This is, again, a real effect, and the apparent paradox (of each seeing the other’s clock as slow) is resolved if you both enter the same frame (are no longer moving with respect to each other).

    Another effect of moving with respect to each other is that what is simultaneous to you, or what happens, first “A”, then “B”, may appear to me in a different ordering, so long as causality is preserved.

    If “A” caused “B”, then we must necessarily agree on their order. We may still disagree on the timing between “A” and “B”, though.

    Some take this as indicating time has no order, but it can be shown to be a simple geometrical effect.

    Just consider two people, roughly next to each other, looking at two poles, one some distance behind the other. A person on the left side of a line connecting the poles will see the rear pole on the left. A person on the right side of that line sees the rear pole on the right. A person dead on the line sees them aligned perfectly.

    And all three are correct. But in no case have the poles shifted in any way. Nor have the people. They just have different perspectives.

    What’s kind of neat about SR is that it’s really nothing more than Pythagorean geometry. Once you get past the whole, “ooh, theory of relativity” thing, it’s actually very simple.

    General Relativity (GR) is a different beast. To fully appreciate it you have to learn about tensors, a mathematical object of fair-ish complexity. (I don’t grasp them, yet, despite several goes at the material. It’s starting to come into focus, but, oh, so slowly. Mike regards them as proof math is made up. 🙂

    GR basically says that gravity and acceleration are the same thing.

    And both of them cause clocks to run slower to those in a lesser gravity or acceleration frame. This, incidentally, means the center of the Earth is younger than its surface, because of the stronger gravity. The center of the Sun is even younger.

    GPS satellites, which are about 22,000 miles out, feel less gravity than we do on the surface, so their little clocks run faster than ours. And because they’re moving pretty fast compared to us on the surface, SR also applies and slows down the clocks.

    Because GPS depends heavily on timing, accurate clocks are a must. So the GPS system has to take both SR and GR into account. We prove Einstein right every time we use GPS!

    (If, for some reason, you want more info about SR, I wrote that series of 25 posts a few years ago that covered the time and simultaneity stuff in great detail with lots of diagrams.)

  • sean samis

    One comment; which I made on Bee’s blog: the example of the Earth’s curvature “emerging” from flatness as we change our perspective is an example of emergence without change. The shape the Earth does not change through this process, it was round all along.

    Only our perception of its shape changes; and that change is distinctly time-ordered. First we thought it was flat, then –after some time– we realized it was round.

    There simply are no good examples of actual changes that are not time-ordered. There’s always a before, and an after.

    sean s.

    • Wyrd Smythe

      (Hi Sean, and welcome to my little place.)

      Yep, exactly. The difference certainly exists at different scopes or scales, but perceiving it or even talking about it requires a timeline.

      I’ve been thinking about how, very long ago, stillness was considered the natural order, because obviously motion always requires constant pushing or pulling. At least in our daily experience. But a simple thought experiment showed that motion had to be the natural state. Likewise, it seems to me, timeless stasis is a hopelessly artificial idea… time flow is the natural condition.

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