The nature of time

I think it’s important to understand the nature of time. That’s because I think it leads to other things. I also think you can gain an understanding of the nature of time by being empirical. For example we use phrases like time flows and time passes, but when you look for the empirical evidence of time flowing or passing, you can’t find any. That’s because there isn’t any. I can hold my hands up a foot apart and show you the gap, the space between them. In this respect I can show you space, so space is empirical. I can also waggle my hands and show you motion, so motion is empirical too.

But I can’t show you time

But I can’t show you time. I can show you a clock, and you might point to the big hand and the little hand and say that’s the time. But what am I really showing you? A box with two moving pointers that go around and around, that’s all. This is the nub of Einstein’s operational definition of time. It’s in his 1905 special relativity paper on the electrodynamics of moving bodies. He talked about trains and clocks, and said this: “Now we must bear carefully in mind that a mathematical description of this kind has no physical meaning unless we are quite clear as to what we understand by time. We have to take into account that all our judgments in which time plays a part are always judgments of simultaneous events. If, for instance, I say, That train arrives here at 7 o’clock, I mean something like this: The pointing of the small hand of my watch to 7 and the arrival of the train are simultaneous events”. This was in a paper about moving bodies. A train is a moving body, so is the big hand of a clock, and so is the little hand of a clock. And the crucial point is that the time is nothing more than the position of the hands. I know that might sound simplistic, but get your magnifying glass out and take a cold hard look at what clocks do.

What clocks do

Open up a clockwork clock and you’ll find a mainspring and a gear train, with an escapement to keep the gears turning at a constant rate. One of the gears is connected to the big hand, another to the little hand. All the clock is doing, is “clocking up” some kind of regular cyclical internal motion:

Clockwork gif  from the Popular Mechanics article Building a Clock by Eric Limer

All clocks do this. It doesn’t matter whether it’s a Victorian pocket watch with a spiral spring and cogs, a quartz wristwatch with a piezoelectric crystal and electronics, or an atomic clock with caesium atoms and microwaves. A clock is some kind of machine which somehow counts or accumulates some kind of regular cyclical internal motion and shows you some kind of cumulative display that you call the time. The gears move so the hands move. Or electrons move and a liquid-crystal display changes. Or something else moves and changes. Whichever way it’s made, a clock is in essence a motion accumulator. It doesn’t literally measure the flow of time. A clock is not some cosmic gas meter. Open up a gas meter and you’ll find gas flowing through it. Open up a clock and you won’t find time flowing through it. All you’ll find is some kind of regular cyclical internal motion. Tick tock, tick tock, the internal mechanism of a clock isn’t called a movement for nothing.

Time does not flow

The notion that time flows is just a figure of speech. Rivers flow, currents flow, blood flows. These things flow because something moves. Water moves, hearts move, people move. The Earth moves, the stars move, the galaxies move. Everything moves, and you can see this motion because light moves to your eye and electrochemical signals move in your nerves and brain. Because photons and electrons and other things move. But you can’t see time flowing. That’s because it doesn’t. Nor can you see it passing. That’s because it doesn’t. The passage of time is just another figure of speech. Footballers pass, buses pass, kidney stones pass. But there is no physical thing called time that actually passes. Instead things move. Things like planets and planes and pendulum clocks.

Time exists like heat exists

That’s not to say that time does not exist. I think it’s best to think of it as something like heat. Heat exists. You know this, especially if you’ve ever burnt your hand on the stove. However heat isn’t fundamental, it’s an emergent property of motion. In a gas the molecules move freely as per the kinetic theory of gases. The temperature of a gas is effectively a measure of the average kinetic energy of its molecules. The faster they move, the hotter the gas:

GNUFDL translational motion gif by Greg L, see the Wikipedia temperature article and Wikipedia Commons

If you examine one molecule, it has no fundamental property of heat or temperature. However if it and the other molecules are moving fast, the gas is hot. This macroscopic property is perfectly real, and it’s why we can cut steel with an oxy-acetylene torch. Time is something similar. Whilst temperature is an average measure of motion, time is a cumulative measure of motion. And time exists like heat exists, because a hundred years t will kill you just as surely as a hundred degrees C.

The arrow of time is an abstract thing

But whilst heat really does flow, time doesn’t. There is no river of time flowing from the past to the future. That’s just an abstract concept for which we have no scientific evidence at all. There’s no real direction of time either. Yes, there’s an inevitable sequence to events, because if you don’t move from A to B you can’t move from B to C. But there’s nothing flowing from past events to future events. People talk about the arrow of time which points from the past to the future, and they talk about entropy. But entropy is merely “sameness”, associated with available energy, wherein energy-density tends to even out as we do work. Entropy increases, but the direction of this is as abstract as the direction of cooling in your cup of coffee. You cannot point in this direction, so there is no arrow of statistical mechanics in any real sense. I can point forwards in space, but you can’t point forwards in time. That’s because the future isn’t a place you can point to. It’s a name we use for the state of the universe after everything has moved. Yes, people say motion is a change in position with respect to time. But when you measure the motion of an object, you use a clock, and that clock merely features other things that move. So you end up saying motion is a change in position with respect to some other change of position. That’s circular. So it doesn’t make sense to say you need time to have motion, not when you can see it’s the other way around. Say it how it is: motion is a gradual change in position. Don’t describe something you can see in terms of something you can’t.

Abstraction can get in the way

This is particularly important in physics, where abstraction can get in the way of understanding. Einstein hinted at this in 1908 when he said “since the mathematicians pounced on the relativity theory I no longer understand it myself”. I think he was referring to his former teacher Hermann Minkowski. You’ve doubtless read Minkowski’s Space and Time which starts like this: “The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality”. Minkowski said this in September 1908. In January 1909, less than four months later, he was dead. He was only 45. I think that if he’d lived longer physics would be different today, because I think he would have seen that the union is between space and motion, not between space and time. But we are where we are, and nowadays some physicists talk about Minkowski spacetime as if it’s the black stuff between the stars. It isn’t. It’s a mathematical model that combines space and time into a single “continuum”. It’s a four-dimensional manifold made up of three spatial dimensions plus the time dimension. We can drop one of the spatial dimensions to depict it:

A manifold is a “topological space”. It’s essentially a mathematical map. It maps out the block universe, which is utterly static because it models space at all times. It’s like you film a red ball with an old-style movie camera, then develop the film, then cut it up into individual frames and form them into a stack. There’s a red streak through the stack. This red streak is the ball at all times, but it isn’t moving up the stack. In similar vein there is no motion through the block universe. That means there is no motion in spacetime. The motion of an object through space “over time” is represented by a world line. But the object isn’t moving up its world line. There is no plate-of-the-present moving up the block universe either. And you cannot look up to the clear night sky and point out a world line. Or a light cone. Or a reference frame.

The map is not the territory

All these things are abstract things, not things that exist. When you are trying to understand those things that do exist, it is important to avoid being distracted by the things that do not. Your reference frame is little more than your state of motion through space. When you accelerate we say you change your reference frame, but it’s not like changing your socks. You’re changing your state of motion, and as a result your measurements change. Your measurements of space and time change, and to make sense of that, we refer to special relativity which in turn refers to spacetime. But it is important to be aware of the distinction between space and spacetime. We move through space, but not through spacetime. Spacetime is the map, but the map is not the territory. Ours is a world of space and motion, not some static mathematical manifold of world lines and light cones. A clock doesn’t really measure the distance between two spacetime points, just as it doesn’t really measure the flow of time. It merely clocks up local motion. That’s all there is to it. It’s as simple as that.

Time dilation

That’s not to say special relativity is wrong. It’s right. Time dilation is perfectly real. We have good scientific evidence of that. Clocks go slower when they’re moving fast, for a very simple reason. I think this is best explained using the parallel-mirror light clock, which features a light beam bouncing back and forth between parallel mirrors:

Public domain image by Mdd4696, see the Wikipedia time dilation article

The scenario is that you and I are identical twins, and we each have a parallel-mirror light clock. You stay on Earth whilst I go on a fast out-and-back trip in my gedanken spaceship. After I’ve landed back on Earth we compare clock readings, and we find that my clock went slow compared to yours. That’s easy to understand when you appreciate that my clock reading is just the number of times light bounced back and forth between my parallel mirrors. Yours is the number of times light bounced back and forth between your parallel mirrors. My light moved diagonally whilst yours moved up and down, so my clock reading is less than yours. My local motion was of necessity reduced by my macroscopic motion through space, because the maximum motion is the speed of light c. You could see this if you had a gedanken telescope, and could watch me zooming across the night sky. You’d see my light beam bouncing back and forth between my mirrors, but because you’re panning, you wouldn’t see my light moving in some zigzag fashion. It would look like it was moving straight up and down. Like your own, but slower. It’s slower by something called the Lorentz factor. Amazingly enough, this is derived very simply from Pythagoras’s theorem. Take a look at the simple inference of time dilation due to relative velocity on Wikipedia:

Public domain image by Mdd4696, see the Wikipedia time dilation article

The hypotenuse of a right-angled triangle represents the light path. The base represents my speed v as a fraction of c. The height gives the Lorentz factor, which can be written as √(1 – v²/c²). If I could somehow travel at .99c, the Lorentz factor would be √(1-.99²/1²) = √(1-.98) = √(.02) = .1414, which is a seventh. So my clock clocks up one year while yours clocks up seven. The Lorentz factor is that simple, and it applies to everything because of the wave nature of matter. Robert Close talked about this in the other meaning of special relativity. We can make electrons out of light in pair production, and we can diffract electrons. Remember what Feynman said about around and around, and think of electron spin as light going round a circular path. Then look at it sideways like this: |. Then set it moving so that the circular path looks like a helical path. Sideways on, it would look like this: /\/\/\/\. It’s just like the light bouncing back and forth between the parallel mirrors, and it’s why time dilation applies to electrons and other particles too, and me, and you.

The twins paradox

This is why if you and I were identical twins and I take the fast out-and-back trip through space, I come back younger than you. But note that this scenario isn’t the twins paradox. That’s where you and I pass each other in space, and you look through your telescope to see my time going slower than yours, and I look through my telescope to see your time going slower than mine. People think this is a paradox, but it isn’t. When we’re separated by distance I look smaller than you and you look smaller than me. But we know about perspective, so we don’t shout paradox! Nor should we when we’re separated by motion, and my time looks slower than yours and yours looks slower than mine. It’s just another type of perspective. Time is relative because motion is relative. Your time is your cumulative measure of local motion. So when you move relative to me, your time is relative to mine.

The time dimension is not the same as the spatial dimensions

This is why the time dimension can be likened to the spatial dimensions. However it’s important to note that it isn’t exactly the same. In special relativity it’s distinguished by a minus sign in the t term in the spacetime interval. This is written as ds² = -cdt² + dx² + dy² + dz², and it is said to be invariant. It’s the same for both my parallel-mirror clock and yours, because our light-path lengths are the same. The time dimension is also different because time is a dimension in the sense of measure, not in the sense of freedom of movement. It’s a measure of how much local motion occurred inside our clocks, nothing more. Hence I can hop forward a metre but you can’t hop forwards a second. Because you can’t move through a measure of motion. That’s why you can’t move through time. You can’t move through spacetime either, because there is no motion in spacetime. Some say you can’t move at all, which is what eternalism says. The opposite view is presentism, which is more in line with Einstein’s 1905 operational definition. It’s also in line with his 1949 view. Palle Yourgrau wrote about that in A World without Time: The Forgotten Legacy of Godel and Einstein. It’s an interesting book. It even mentions time travel.

Time travel is science fiction

Talking of which, I love films like Timescape, 12 Monkeys, and Déjà vu. They feature time travel, as do many more. I love them even though I know that time travel is science fiction. I love them even though I know why time travel is science fiction, and why time travel to the past is out of the question. It isn’t because of the grandfather paradox or the chronology protection conjecture. It’s because we don’t even travel to the future. Travelling to the future is just another figure of speech. Yes, you may have seen Stephen Hawking saying you can travel to the future on a superfast train:

Still from Stephen Hawking – Train Ride to the Future from into the universe with Stephen Hawking

But you aren’t really travelling to the future. Instead you’re affected like the parallel-mirror light clock. As the train speeds up, the local rate of motion in your body and brain has to reduce. If it didn’t, adding your local motion to the train motion would mean the total motion exceeds the speed of light. That can’t happen because of the wave nature of matter. So you’re time dilated, that’s real enough. But you aren’t travelling to the future, any more than I am sitting in my chair. I’m not travelling to the future at one second per second, and you aren’t travelling to the future at seven seconds per second. You’re just living your life in slow motion for a while. And whilst you’re doing that, I can watch you every inch of the way. You can look out the window and watch me every inch of the way too. You don’t disappear up some time tunnel to start living your life in the middle of next week. You’re living your life in slow motion so you effectively fast-forward through the week. Like bullet time in reverse. Then when you step off the train it’s me who meets you at the station. I don’t miss you by a week. You slowed down your time by slowing down your local motion, that’s all.

The stasis box

It’s not unlike those films or TV programs such as a kind of stopwatch where the protagonist has a device that can stop time. If you look carefully, you’ll notice that what the device really does, is stop motion. One such device is the stasis box. When I put you inside, everything stops. Electromagnetic waves don’t propagate, electrochemical signals don’t travel in your nerves and brain, and electrons don’t move. So you can’t see, you can’t hear, and you can’t even think. Hence when I open the door a week later, to you it’s like I opened the door just as soon as I closed it. It would feel like you’d “travelled” to the future in an instant. But you didn’t move, you were totally motionless. Instead everything else moved. Yes, the stasis box is science fiction too, but don’t forget that we can freeze embryos today. Someday we’ll perhaps be able to freeze an adult and thaw him out with no damage and no loss of memory:

Cryogenic vats image from the Cryonics Institute

Then you could “travel to the future” by stepping into a glorified freezer. But you aren’t really travelling to the future. The freezer is like the stasis box, but it works at the biochemical level rather than the subatomic level. Either way, you aren’t moving. Instead everything else is. The crucial point is that there isn’t really any travelling forward through time. There is no way you can move to get to next week. The Earth turns seven times, then it’s next week come what may. There’s nothing you can do about it, whether you’re sitting on the superfast train or in your armchair at home. You can’t travel to the future just as you can’t climb to a higher temperature. There is no cosmic rewind button. And there is no way you can move such that all other things not only move back to where they were, but never moved at all.

Closed time-like curves do not permit time travel

So don’t think that closed time-like curves permit time travel. Because they don’t. Because spacetime models space at all times. So there is no motion through spacetime. So there is no motion along a world line. So there is no motion around a world line that curves full circle. See A World Without Time again. See page 142 where Palle Yourgrau says Wheeler conflated a circle with a cycle:

Fair use excerpt from Palle Yourgrau’s A World Without Time : The Forgotten Legacy of Gödel and Einstein

He’s right. If your world line was a 24-hour closed time-like curve, it wouldn’t be time travel, and it wouldn’t be Groundhog Day either. It would be more like Mayfly Day. You hatch from an egg, you live, you lay that egg, you die. You live only once, for 24 hours only, and yours is a life without cause and effect. That isn’t like the real world at all.

Wormholes are science fiction

In addition, don’t think that you can travel through time by going through a wormhole. Yes, some physicists talk about traversable wormholes, and say you can use wormholes for time travel. Others say they’re associated with black holes, and say all you need is some negative energy, and you’ve got yourself an Einstein-Rosen bridge:

GNUFDL wormhole image by Kes47, see Wikipedia Commons

The trouble is that there is no negative energy, just as there are no negative pencils. There are no Einstein-Rosen bridges either. If you’ve ever read Einstein and Rosen’s 1935 paper you’ll know it’s about the particle problem in the theory of general relativity. They talked about a mathematical representation of space wherein a particle is represented by a bridge connecting two sheets. It isn’t anything to do with the popscience wormholes you read about today. They grew out of David Finkelstein’s 1958 paper past-future asymmetry of the gravitational field of a point particle. He was talking about point particles and antiparticles, and saying an antiparticle was some kind of white hole, which it isn’t.

There is no time travel

Bear all this in mind next time you read some book by some celebrity physicist claiming that backward time travel is governed by the laws of quantum gravity. Because it isn’t. Ditto if you see some celebrity physicist waxing lyrical on the Discovery Channel about how to build a time machine. Because you can’t. Because time dilation is a reduced rate of local motion, and things can’t go slower than stopped. Which means that there is no need for any chronology protection conjecture, and no need to worry about the grandfather paradox. Because motion is motion whichever way it goes, and there is no such thing as negative motion, just are there are no pencils that are less than zero inches long. You can’t travel back in time, or forwards, because time is merely a measure of motion, and motion is travel, and you can’t travel through travel. All you can do is step into that glorified freezer or slow your life down some other way, then wait for the world to change.

Why clocks go slower

You might feel a little sad that time travel is science fiction. But there’s something that more than makes up for it. Something that’s glistening down there in the smouldering ruins of the TARDIS. Something shiny. Pick it up and dust it off, and you find it’s a key. A golden key. It’s the key that opens all the doors in physics, and it’s this: clocks don’t go slow because time goes slow. It might not seem like much, but it is. That’s because it applies to all types of clocks, including optical clocks. Think on this: if your clockwork clock was going slow, and I told you it was because time was going slow inside that clock, you’d laugh in my face. Because you know full well that if your clockwork clock was going slow, it’s because the clockwork was going slow. In similar vein an optical clock doesn’t go slower when its lower because time is going slower inside it. It goes slower for another reason entirely.

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This Post Has 26 Comments

    1. Hello Zephir, how are you keeping? You’ll be pleased to know that Newton thought of space as an aether. See Opticks query 20: “Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines?” So did Einstein. So did Schwinger and others. See the quote by Robert B. Laughlin here: https://en.wikipedia.org/wiki/Aether_theories#Quantum_vacuum

  1. “That’s where you and I pass each other in space, and you look through your telescope to see my time going slower than yours, and I look through my telescope to see your time going slower than mine”
    Hi John, The Twins paradox isn’t that. Instead the twins paradox is when one twin goes to, say a star at close to light speed. Then he turns around and comes back. The paradox is as follows. The travelling twin returns younger, even though, from the perspective of each twin, they have *both* been moving – relatively to one another – at close to light speed.

    1. See Wikipedia: “The paradoxical aspect of the twins’ situation arises from the fact that at any given moment the travelling twin’s clock is running slow in the earthbound twin’s inertial frame, but based on the relativity principle one could equally argue that the earthbound twin’s clock is running slow in the travelling twin’s inertial frame”.

  2. “Time travel is science fiction” – all you need to travel through time is go faster than your surroundings and hey presto, you’re in the future (relative to your surroundings). Travelling through time in the opposite direction is, according to the laws of physics as currently formulated, science fiction – unless you allow for Quantum Mechanics and the uncertainty principle, where quantum systems can perform time travel tricks, as measured by experiment.

    1. Remember the stasis box. You don’t really “travel” to the future, You aren’t moving inside that stasis box. Instead, outside that box, everything else is. (I’d like to say I could stand there looking through the porthole looking at you all frozen in stasis for a week, but light doesn’t move, so I can’t). As for quantum mechanics, I take a “realist” view, and view the delayed choice quantum eraser as a mere trick. Not time travel.

  3. What qualifies as time travel is semantics. I say that we time travel when we move because that’s how I interpret the lorentz contraction. You say we do not due to the stasis box. It’s a fun philosophical debate 🙂

  4. As for quantum mechanics, you have to consider that the uncertainty principle means that particles not only an uncertain position / momentum, but also an uncertain time / energy – and therefore particles must by logic – travel through time relative to one another.

    1. The Heisenberg Uncertainty Principle is just a wave thing. See Wikipedia: “It has since become clearer, however, that the uncertainty principle is inherent in the properties of all wave-like systems,[8] and that it arises in quantum mechanics simply due to the matter wave nature of all quantum objects”. It’s the wave nature of matter, that’s all. That’s why we can diffract electrons. Waves in the ocean don’t travel through time relative to one another. Nor do seismic waves in the ground. And nor do waves in space.

    1. One day Amrit, everybody will be on this same page. The page where it starts. Let’s hope it’s sooner rather than later.

    2. “In space is always NOW” – not according to Einstein it isn’t! 🙂

  5. Hi John,
    here you are now. I always liked your answers in physics.stackexchange a lot, because they go beyond just citing formulas and the “shut up and calculate” that most others prefer in their answers (even for non-quantum questions) . I wonder why they suspended your account. As far as I understand it, you don’t disagree with the formula stuff, but I guess your interpretations, your understanding, of the formulas is deemed non-standard.

    Well, lets come to “time”. You say the progression of time is intimately linked to the speed of light, agreed! You describe time as motion and compare it to heat and I nearly agree. But while heat depends on the mean-square of the speed of the involved particles, time, i.e. $d\tau/dt$ rather depends on the variance of velocities of a bunch of photons if you treat them as point particles. Which is why $d\tau/dt=0$ if an object moves at the speed of light: all photons (and possibly other “particles” with zero mass I guess) then have identical velocity (i.e. absolute value =c and identical direction), so their variance is zero. The derivation of $c d\tau/dt = \sigma(v_i)$ is rather simple: http://www.pifpafpuf.de/2017-11/More-Time-Again.html#phyicstime .

    I find this “mechanical” equivalent for time quite convincing:-)

    P.S. Would be great if you could activate MathJax on this site.-)

    1. Harald: I think it was because my answers were very good, with excellent references. So much so that a resentful cabal saw me as a threat, conspired to downvote, and then suspended me on specious low quality grounds. Not good. But all too common I fear. I am reminded of peer review by Nick Kim:

      Yes, I think time is straightforward. It beats me why people make such a big mystery of it. It’s almost as if physicists these days are peddling myth and mysticism instead of offering answers. IMHO the important thing is that when you understand time, you understand that the speed of light is not constant. Then with a little light reading of the Einstein digital papers, you understand gravity. Then you understand that curved spacetime isn’t curved space, so you ask yourself what is. There’s this step-by-step logical deduction that takes you places. See the other articles.
      .
      PS: I’ll take a look at installing mathjax. I see there is a plugin for it. But right now I’ve got to cut the hedge before it gets too hot!
      PPS: Mathjax installed!

  6. you kind of lost me, when you said “I can point forwards in space, but you can’t point forwards in time.” + “Don’t describe something you can see in terms of something you can’t.”; that’s a cyclop[s]ian way of looking at it… if one puts in enough words, one could do the same “explaining away” with the other 2 basic quantities of interactions in space (“length” and “speed” that is); what is “forward” anyway, in a Copernican universe???
    … and that I say besides the fact, that I would otherwise be inclined to agree with you, that circular definitions are [somewhat] flawed (but then again: maybe inevitable, once one touches upon the fundamentals of that what is knowable? – it’s not like there is an absolute canon of terms one can rely upon and which are beyond reproach (as far as criticism and skepticism go), self-reliant and eternal) — or let’s say: “problematic” (like when defining the speed of light via hard definitions of time and space which, in turn, are “measured” via light[years] and “atomic” clocks – i.e. circular reasoning; tautologies). — What’s knowable anyway? – what’s “knowledge”? – what’s “truth”? – that, my friend, is definitely a concern for philosophy, not science… science deals with [so called] “facts”, for which the principles of observation and [therefore] measurement have to be “known” [+handy] in “advance”, be that via induction, consensus, or epiphany or – whatever! … it’s good to keep an open mind, but you are scratching the limits of what is possible to be answered from “within” physics, rather than – beyond.

    besides; I suspect “time” being a “quality” of “space”, a [modus operandi of] falling into the unfolding [so called] “spacetime” of the universe, as long as that “expansion” can and will go on, and whatever (allegedly obscure (“dark”) thing [that]) drives it will be depleted … but then again: what do I know! – Que sais-je?

    “All these things are abstract things, not things that exist.” – so is mathematics. What’s your point? – it’s almost as if you refuse to quantify time, as it would take away the concept of “free will” or the heart-warming mystery of a non-deterministic future or — whatever! If space is “real”, so is the “dimension” that bridges one end of it to the other over a course of action (which does not automatically imply, that it could be reversed!). There are moments when “factoring out” time will be useful (i.e. yielding bits of knowledge), and moments where it will not…

    [- posting this before moving on in the text; which may be deemed a bad reading-habit… but I have this bad habit, anyway (and can’t shake it), which is called “thinking for myself”; and too much of that at the most inappropriate moments. — “Müßiggang ist aller Philosophie Anfang. Folglich—ist Philosophie ein Laster?” (F.N., Notebooks, Frühjahr, 1888, 15 [118]) -]

    PS: a better argument could be had, still, on behalf of your position, from a memory/history pov — probably; as time being the experience of experiences, of the data-collecting mind; the librarian (“us”) musing over the library-index, thinking it to be a thing of itself; meta-experiences for meta-physics… my point still stands, but it would be a better entry-point to a discussion about this special quality of problems; and it would still be a problem from the domain of philosophy, rather than physics…

    1. If I lost you when I said I can point forwards in space, but you can’t point forwards in time, then think about science deals in facts. Remember that I can show you space and motion, but you can’t show me time. And that when you look inside a mechanical clock, you don’t see time flowing through it.
      .
      I think there’s more that’s knowable than some people think. And that William Kingdon Clifford more or less nailed it with his space theory of matter. I don’t think I’m scratching the limits of what is possible to be answered from “within” physics here. I think I’m only scratching the surface. This is where it starts, with time. After you understand that, you understand that the speed of light is not constant, then you can understand gravity. Then when you understand that a gravitational field is not curved space, you ask yourself what is?
      .
      My point is that the scientist should be empirical, and not allow himself to be distracted by abstraction.
      .
      Philosophy is not a vice. It isn’t necessarily a domain that is distinct from physics either. Ask any physicist with a PhD.

      1. “Remember that I can show you space and motion, but you can’t show me time. And that when you look inside a mechanical clock, you don’t see time flowing through it.”
        I like that logic; “I cannot smell air – therefore it can’t be real” (sorry, I just cannot resist the urge; I honestly mean no offense by this!)
        I can show you time; but it is directly pointing away, when I show it, in the line of sight; you look through the dimension, rather than onto it, when looking into deep space. There: you have it! – you can’t ever zoom out of it, to look onto it’s extension; that’s sadly how things work…

        “And that William Kingdon Clifford more or less nailed it with his space theory of matter” – I’m still reading; again, my apologies, for posting before having reached the end, Bad habit, no doubt about it. But some things I just have to get off my chest (or whatever that thing’s called at the upper end of my neck), before moving on, for a semi-fresh start…

        “Then when you understand that a gravitational field is not curved space” – o/c not! – it’s curved time! – “space” only behaves in such a way as it was curved with it (or rather: the things within it, behave in such a way, to make that impression), and, as special beings, we are more prone to see the secondary, perspective-phenomenon, as the real one; oh… that isn’t what you meant 🙁

        “My point is that the scientist should be empirical, and not allow himself to be distracted by abstraction.” I really don’t think that that’s what you meant to be saying; (also I think, that what I commented on, concerning “mere philosophy”, was necessarily what you meant to say with that) You rather seem to value (that’s my impression), thinking for oneself and understanding in-depth (which naturally inclused “theorizing” – in order to narrow down other people’s theories we try to understand; learning is recognizing patterns – by comparing it to known patterns…), where others only cling to mathematical formulas, like some disabled person to a wheelchair (was that a sideblow on anybody? – I don’t know…), or the proverbial grudges… empirical is to only see w/o interpretation, pure and mindless; which always ever happens in a fairy-tale world of true-vacui, timeless pictures and perfect observers…
        Btw.: you mentioned some book about physics getting lost in mathematics? – sure I kept it as a link, somewhere… something about “physicists getting hung up on beauty” (as in elegant formulae)… I think I’m gonna read that, but I think the author is wrong to suspect “beauty” as the driving force. I think it’s fear. The taste for expressing everything in terms of math-formula is that of a fearful kid who cannot cope with the world. Which isn’t meant as an insult, as thinkers, in general, are more prone to vita contemplative rather than vita activa, and phobic-behavior or at least careful hesitation naturally comes with that — or rather: may be it’s prerequisite in many cases. But among all kinds of thinkers, in my experience, “born” Mathematicians are usually worst in that regard. If there ever was a generral study on mathematicians, shyness, reluctance to act, proneness to precaution-measures that others would deem ridiculous – I am sure such study would find some great trend in said flock of people . . . Math-formulas are often — like grudges/preemptive weaponry, depending on the respective circumstance/needs; something to hide behind from criticism (and to absolve oneself from pesky necessities, like the need to think for oneself, be quick on one’s feet, reevaluate held believes); something to adhere to like the proverbial “argumentum ad auctoritatem” (math IS an authority! – but today it rules over physics [it seems] like a despot, via the inept and semi-intelligent who see it as their best clutch for power!), something even for the lame and the slow and blind to cling to in a desperate attempt to keep their head above water . . . And that’s not saying, that they are generally useless; them being weaponized rather proves their power; but power can always be misused, and even paralyze the user…

  7. “The height gives the Lorentz factor, which can be written as √(1 – v²/c²).” – does it, though?
    If light travels at a not-absolutely-constant speed (at least according to the gravitational potential it is moving at; something you allude to, in another article), while we measure it’s speed -always- from our limited perspective (which may skew the picture systematically), shouldn’t it at least read “c₀²” (like in “c = c₀(1 + Φ/c²)” )?!? – which, in turn, would have important repercussions on past-day speed-of-light experiments(*), from before special-relativity-theory…
    The Lorentz-transformations keep giving me headaches; to me, it seems, by transforming what is happening, one is dodging – for convenience – what is really going on. But I am esp. confused by the notion I picked up elsewhere (in explanations concerning the M.Morley-experiment), that time and space are distorted in the direction of “ether-drift” ONLY. – which the paragraph I pointed to, seems to deviate from.
    Sorry, again, for asking ignorant questions…

    Also: “Remember what Feynman said about around and around, and think of electron spin as light going round a circular path.” – doesn’t that directly contradict something you wrote elsewhere, about “light clocks” (thereby equated to time itself, which it was supposed to merely “measure” – which you rattled against) not really going faster at higher altitudes? … think about it this way: if all processes are, via spin, and movement of electrons “similarly” to light slowed down/sped up via gravitation, doesn’t that mean, that time (or the “flow” thereof) itself was running slower/faster under these conditions, for all particles therein (in the given [particular] frame of space-time that is)**; it’s quite impossible, to throw out time like some sort of merely abstract category if it can, from the perspective of “stuff therein” be more or less. Something that is 0, cannot be multiplied to be anything but 0 . . .

    Also: “In space is always NOW” (not your statement, but still) – no. SpaceTIME is always HERE AND now! (If “Space is always now”, then [it logically follows that] “Time is always HERE”!) … as soon as we look far away from that tiny quantity that we can grasp, into the depth of space, we are looking into the past . . . Not sure, why so many people seem to have a problem with that “4dimensional map”, as it does not automatically(!) follow, that it perfectly outlined the future and everything in it with it (if that was their concern); or that life was something free-willing and creative to begin with, that would feel horribly demeaned by such a perspective; it would not… only our romantic sentiments are!

    [- boy… not even halfway through; already I feel like a nuisance; esp. since pausing for 24h -]

    *) speaking of which… Did you ever come across “Gezari”, by any chance? There are two papers of his (strongly linked together, one heralding the other) I read very recently, that got me intrigued; esp. considering some of the papers he alluded to (esp. “Consoli and Costanza (2003)” – suggesting, in essence, that past ether-drift-experiments (read with some adjustments?) did in fact suggest a certain ether-drift of 204±36 km/s), which I, sadly, cannot find/access.
    I mean this: arxiv.org/abs/0912.3818v2
    And this: arxiv.org/abs/0912.3934v3 (did he make an error? – I don’t quite get why he exchanged the formula, towards the end… did I miss the explanation? + how did Neumann (2008) & Murphy (2008) calculate D_LB & D_BR ?!?)

    **) What’s “space” anyway, with (/if it had) nothing “in it”? – again: the same logic with which you start to undercut the reality of time works for space itself just as well; same with looking-into-the-past-with-every-use-of-a-teleskope . . .

  8. “The time dimension is also different because time is a dimension in the sense of measure, not in the sense of freedom of movement.” – again, some flawed logic. If dimensions are only dimensions, because one can “move” (what even is movement?) through them, then there is a 4th dimension, that naturally follows out of the 3, that one can be caught up in (!) at “any given moment” (to bind together all states of that slate, all single incarnations; “One ring to rule them all”); You know: I’m kind of inclined to say “you are not even wrong!”, with these sorts of statements – in the proverbial sense. Well… you kind of are, as you have to turn to and turn away from, the thing you try to explain away in order to explain it away. So — you ARE?! Time is not one of the 3 dimensions we can directly observe, in a still-frame. If that’s where you are coming from: gotya! — but that still-frame is an abstract idea in it’s own right (we wouldn’t even “see” anything to begin with, if time would not connect us to the past still-frame we want to observe!), which you generally tend to degrade (“abstraction”, that is)… I’d also give you, that it’s debatable, if time was really just “one” dimension to the other 3, an equal fourth sibling from the “space-time” quadrupled; an argument could be made, that it was at least 2 dimensions (or more? – or a half?), of height of potential and depth of field, which transform into one another in a – possibly – non-linear way. But that’s pure speculation.

    PS: gotta love these: https://picload.org/view/dlllcddi/captcha-findedasfahrzeug2.png.html
    https://picload.org/view/dlllcddw/captcha-findedasfahrzeug.png.html

  9. “It’s a measure of how much local motion occurred inside our clocks, nothing more. Hence I can hop forward a metre but you can’t hop forwards a second. Because you can’t move through a measure of motion. Hence I can hop forward a metre but you can’t hop forwards a second.”
    I really really do think, that all these arguments, for why time wasn’t what everyone was allegedly convinced it was, were leading up to something important you have to say — but I really really am not buying it; the arguments just do not work.
    I cannot hop forward a second as much as I cannot quantify a feeling, touch the wind or eat a thought or — whatever! … as it is the wrong procedure “to get there”; it happens anyway, unless I die within 0.9999 of a second, w/o delay, like being disintegrated on a molecular level or something; other than that time will just hop me over there on itself. I cannot vacate the total space I am occupying (yeah yeah; I can lose some weight; stop pressuring me!); nor can I prevent my future me to occupy a space just like that when the time comes for it to just “be”; I’ll fall into that existence by mere virtue of being “now” (and, like I said: not immediately dying in the mean time).

    “That’s why you can’t move through time. You can’t move through spacetime either, because there is no motion in spacetime.” — entirely tautological reasoning. – besides: you most definitely cannot move through time, either, as that involves -you guessed it- TIME. Strictly speaking: “you” can’t do anything. You are hear and now, for that split of a second. “your body” will move on, to manifest your future “you”, which will be, again, a momentary event of thought. Your memory will make, that that future you will believe in the continuity of the self, constituting life [as something “more” than just a long line of biochemical processes]. The “identity” of a person is a fiction of our imagination, as a useful outline to cope with the world, just like separating it into useful objects and tools serves us to make ourselves feel at home in that fiction. – but does any of that mean, that the idea of “self” and “Identy” was obsolete in it’s entirety? Just because something “isn’t quite” what some people naively make it out to be, doesn’t mean, that the opposite of said skewed believe was reality. – now… maybe my arguments will “make as much sense” to you, as yours make to me; and that you see me trying to communicate something to you, that seems flawed; even if you can guess (or not?) that there’s an important thought wrapped inside of that set of arguments; and it will all seem futile…

    “Philosophical presentism is the view that neither the future nor the past exist” – as a German, I feel like seconding that thought… it really makes for a much smoother cop-out for any sort of blame being put on me for whatever suppsoedly happend some 70 years ago… rather than having to explain that even my grandparents were much too young to had have a stake in – whatever that was? – I just pull that get-out-of-jail free card. Facts are pesky to communicate; all encompassing philosophical principles, however, can be bullet-proof, like religious believes…
    Now, on a serious note: that idea is both self-consistent and flawed. A piece of logic that is detached from any sort of further investigation, or connection to reality (be that “something that really is”, or a mere “fiction thereof”). It’s basically un-falsifiable (“not even wrong”); like Hawking-radiation (“Just you wait a quadrillion-years, till the first black holes have reached their end! – you’ll see! – great big lights going off, everywhere! – until then, you cannot prove or disprove it, therefore it is true!”) Again: this idea is self-consistent, and similar thoughts have come to me also, at times. But as far as theories go – it’s an island, with no bridge connecting it to the rest of the observable universe… Philosophy can be like that at times. Just look at Berkeley’s materialism for that matter…
    …but I’ll try to resort to more well-behaved questions rather than relentless second-guessing (sorry about that), and more “self-apparently” constructive criticism (if there even can be any), from hereon out. 🙂

  10. x) the train to the future – I gotta ask: doesn’t that violate the “no preferred frame of reference”-conjecture? – the time of the guy in the train will look going slower from the armchair-observer; while from his own perspective, it should be the armchair-sitter who’s actually aging slower; which means, even with all that being said, there is no “going to the future”, neither via warping there, nor via time-capsule or super slow-mo living…
    Again and again I realize, that while there is good evidence for General Relativity, in the precession of Mercury and starlight being bend around our sun as witnessed during that famous sun-eclipse (1917? – certainly repeated afterwards) – special relativity cannot quite claim the same for itself (it rather seems like an abstract, that dodges the understanding of the real phenomena in relativistic movement). I’ve actually never seen spacial dimensions of fast moving objects getting shortened in the direction of flight, or proof that time really does run slower for that. It’s a nice, intriguing theory… but I keep seeing the thought-experiments being recycled and reworded, time and time again, w/o any real world examples (though I find that even more important for the second postulate, of invariant light-speed) . . .
    If you are still reading what I write, but don’t care to comment on those many paragraphs with “stupid” questions, at least this here, I hope, getting an answer to. :/

    y) “Someday we’ll perhaps be able to freeze an adult and thaw him out with no damage and no loss of memory:” – that’s also science-FICTION. Any attempt to freeze a person will ultimately destroy pretty much all the cells in his body, as the water freezes, and ice-crystals rip open the cellular walls… good luck with waking up with that!
    I’d rather have my mind being loaded into a computer, to emulate it’s processes and for “my self” to be preserved in that, as some not-entirely-artificial “AI”, freely roaming the web + beyond — rather than having the “luxury” of dying of frost-burns, some time in the far future. Even though, technically speaking, that “self” wouldn’t really be “my self”; it would be a copy, whilst I would still be standing on the outside, looking in, thinking “if only!”… or maybe I’m lucky, and Helios finds me. Or Daedalus…

    z) concerning “closed time-like curves”: in that wiki-link it says: “and since then other GR solutions containing CTCs have been found, such as the Tipler cylinder and traversable wormholes. ” — I hate it when they do that. “[solutions…] have been found” — as if there was a real finding rather than just a model (the average reader hardly distinguishes between “solution for a real life problem” (e.g. “IT-solutions”; as they are often advertised everywhere) and mere “mathematical solutions” to work on paper) that has no basis in reality. Mathematical shenanigans, overstated for means of wishful thinking… Sometimes it’s just a matter of wording; but it betrays the mindset of the author (like with wikipedia), and thus forms the mindset of many readers, who then get out of the article thinking (for instance) white holes were real…

    aa) “He’s right. If your world line was a 24-hour closed time-like curve, it wouldn’t be time travel, and it wouldn’t be Groundhog Day either. It would be more like Mayfly Day.” – wouldn’t it be more like a cut-out portion of spacetime, like a miniature-[island-]universe within the universe, w/o any causal connection to “the outside” (and as such entirely w/o consequences for the outside, also; which may as well be synonymous with “non-existent”! – “unreal”!)? – but then again, I am not reading the math…

    ab) ” You live only once, for 24 hours only, and yours is a life without cause and effect.” – cough “Lost Highway” cough (ever seen that movie?)… not that I truly want to recommend that, or bring up another “[mathematical] solution” like a Möbiusschleife…
    ac) “all you need is some negative energy” – reminds me of Hawking-radiation. “Negative energy particle” … oh, those painful facepalms… “there is no such thing as negative energy” (S.Hawking)… he wrote so himself (I may be paraphrasing), in one of his books. Funny how that goes…
    ad) “paper past-future asymmetry of the gravitational field of a point particle” – behind “paper” I only get a google-search (which works for me, but not sure you intended that to be the actual link? – or is this for legal concerns???), the other one again does not let me view the actual paper.
    ae) finally, I am finished!
    Boy… some misunderstandings and redundant criticism may have been avoided, if this article was titled “putting the fiction in science fiction” or “Why time-travel is pure popscience”… something to that extend.
    af) “You might feel a little sad that time travel is science fiction.” I never felt like this. I see scifi for what it is: science-fiction! – if that works on the premise of some science-mumbo-jumbo thrown in to gaslight critical thinking just enough for time travel to be real, or for wormholes designed for faster-than-ilight travel opening up a door to some Lovecraftian hellish other dimension (“Event Horizon”)… it still beats being told, that “love” can “bridge space and time” (“Interstellar”), or that skyscraper-high war-robots can fly into space in a matter of seconds, with their spacesuit-wearing pilots incapable to breath, while those same robots can handle the enormous pressure on the bottom of the Mariana-trench (don’t even ask, if you have to; just be glad, that you dodged that logic-bomb)…
    anyways… no offense! – if you are even still reading this, sorry for the loads of text.
    If you actually did read it, though, I still hope you can take something away from it, non-the-less. As I was actually meaning well, with constructive criticism, on some of the introductory arguments you gave…
    PS: I enjoyed the bottom third much more than the other parts…

  11. where did my last reply go? -.-
    was it auto-marked as, because of the frequency? – or am I blocked?!?
    Or did you manually erase it? -.-
    It was actually the most positive of all the replies; but now it is as if it didn’t even happen… very disappointing!

    1. No, you aren’t blocked. Perish the thought! Your last reply went into the bin. I can’t see why. I had a bad attack of pharmaceutical spam a while back, and still have a long blacklist of words like “viagra”. Anyway, I have now restored it. Apologies for not replying already, I was busy at the weekend and now I’m at work. I’ll respond later.

    2. Yes, the height gives the Lorentz factor. It really is Pythagoras’ theorem at work.
      Yes, when you include gravity you need to include that Φ term, but this article is talking about SR.
      Lorentz transformations ought to be a headache in terms of length contraction, because you don’t get shorter when you move fast. But it’s no problem re time dilation.
      Re electron spin, think of a helical spring. When you stretch it out, from the side it looks like the zigzag path of the parallel-mirror light beam. There’s no contradiction. Imagine you can watch the zigzagging light beam through a telescope which is panning from left to right. In your field of view you see the light beam moving straight up and down at a slower rate.
      Re “In space is always NOW”, the map is not the territory. We live in a world of space and motion, not in some 4D spacetime.
      I don’t know about Gezari I’m afraid.
      .
      You can feel the air blowing in your face.
      Sorry, I don’t understand what you said about “I can show you time”.
      A gravitational field isn’t curved time! It’s inhomogeneous space.
      Sorry, but I meant what I said about being distracted by abstraction.
      Yes, I value thinking for oneself and understanding in-depth. A mathematical formula isn’t enough.
      The book I mentioned was Sabine Hossenfelder’s. See this.
      IMHO the driving force is beauty, not fear. See the monopole article, which I posted today.
      Yes, I think maths is sometimes the basis for handwaving and smoke-and-mirrors from people who peddle Emperor’s New Clothes.
      .
      Yes, the time dimension is different because time is a dimension in the sense of measure, not in the sense of freedom of movement. I can move in the space dimensions. You can’t do that in the time dimension. It’s that simple. Don’t overcomplicate it.
      .
      You can’t hop forward a second but you can touch the wind – just stick your hand out of the window. As for feelings and thoughts, they are qualia. They’re nothing like time.
      Not being able to move in spacetime isn’t tautological. Spacetime models space at all times. So it’s totally static.
      You can’t move through time but you can move through space. Don’t try to block that out by talking about your body, thought, and memory, or about identity and self.
      The future does not actually exist, it’s just the name we use for the state the universe will be in once things have moved. The past is the name we use for the state of the universe prior to things moving to their current location. Don’t worry about being German. People are very good at being foolish, especially when they are convinced they are somehow superior.
      What idea is both self-consistent and flawed? I am not a fan of Hawking radiation.
      .
      The train to the future doesn’t violate the “no preferred frame of reference” because it’s accelerating. It’s like the twin who travels out and back.
      I share your sentiment re length contraction. In fact I would say fast moving objects get lengthened, not shortened. But that’s no reason to doubt time dilation. Check out muon decay. Muons last longer when they move fast.
      Yes, freezing adults is science fiction.
      So is uploading your mind into a computer. It won’t preserve you. A copy is not you, just as your twin is not you.
      Yes, a solution might have no basis in reality. I have previously used the example of a negative carpet measuring -4m x -4m.
      Yes, if your world line was a 24-hour closed time-like curve it would be like a universe within the universe with no causal connection to “the outside”.
      No, I’ve never seen Lost Highway. And after reading about, it I don’t think I want to.
      Wait until you read what I say about Hawking radiation. You will be pleased.
      I’ve changed the hyperlink on “paper” preceding past-future asymmetry of the gravitational field of a point particle
      All points noted re “Why time-travel is pure popscience” and “love” can “bridge space and time” (“Interstellar”) et cetera.
      As for the last third, try reading it all again, in a week.

      1. *sigh*
        You aren’t even reading, what I actually wrote.
        “So is uploading your mind into a computer. It won’t preserve you. A copy is not you,…” — read again. I can hardly even skim through your answer, let alone finding anything useful in there, if you don’t even read what I wrote in the first place. One cannot answer what one did not pay attention to. :l
        I basically skipped the middle part, and am at a loss, to muster the perseverance, to read and reply for real.
        Ever since you mistook mentioning of “c0” being the same as to necessitate that gravity ITSELF was to be taken into account, I lost confidence in this… I never said such a thing! – All was trying to allude to [carefully], was an inconsistency of yours, where you treat speed of light as variable (see other article) when it fits your ideas, and as invariable when it does not . . . like is the norm with so many others. It’s really tiresome… -.-
        “[…] try reading it all again, in a week.” – dito. If you don’t feel like actually doing justice to what I wrote then, well… there’s that. If I did not make myself clear, I am sorry, non the less. As I said, english isn’t really my first language, so any bumps in the reading experience (of that which I wrote) may lead up to greater misunderstandings, thanks to the loss of flow; it’s understandable, but with that also… probably useless :l
        *disappointed*
        I really wish you would have read those 2 Papers by Gezari I linked to… as I would really like to learn, if there ever actually where any experiments to prove, outside any lab (closed frame of reference…), w/o any pre-conceived notion that it “Must be such and such” — if “c” actually WAS invariable. For I am suspecting, more and more, that it is not. In terms of gravity you already concede that — but in terms of special relativity, the opposite was suddenly true. Whenever speed of light is deemed invariable, it’s obvious, that it is made to save-guard the continuity of ongoing research; which is the opposite of scientific.
        Maybe there is no objective way to ever test that; and the meter being defined by the speed of light being defined by the meter, may just be the circular reasoning most feel we “HAVE TO” resort to, in order to have a basis (any basis) for solid scientific findings and theories … but there’s that — it’s a purely opportunistic form of pragmatism). So, as a pyrrhonean I am having my doubts, non the less. As I do about dark energy and dark matter, the phologistons of our day and age. And Hawking-radiation…
        Have a good one! :l

        1. Sorry you didn’t like my reply CG. But cross my heart and hope to die, I read through your comments carefully, step by step.

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