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?Strange? interpretation of Time-Dilation and it's implications

  1. May 14, 2008 #1
    First of all, I'm an electrical engineer, I had to take a class on modern physics, so answers don't need to be "dumbed down" so let me START with the question: Can anyone see a flaw in my logic/interpretation of what's happening? My goal is to gain a more accurate conceptual (not mathematical) picture of what's happening (in as much as we can ever really 'conceptualize' it.)

    Here are some initial assumptions:
    1. The worldline is specific to an observer.
    2. The observer is located at the origin of the worldline.
    3. The origin of the worldline is a dimensionless point that represents the "here and now".

    Ok, so then that means that no matter where you define the 'origin' to be, that every point in the observer's body is space-like separated from every other point in their body -- If the origin had any width or dimension to it, then the light-speed boundary would necessarily be violated. (I'll leave any 'Quantum Uncertainty' in defining the exact location of the worldline origin for another post)

    I'm thinking of the worldline origin as the 'primary' location of observation... I won't go so far as to say it is the location of 'consciousness' because really you can put that point anywhere... in your foot, between your eyes, etc... The important thing is that in order to not violate relativity, you MUST have a precise dimensionless point of reference. Everything else is secondary and SEPARATE from that point, just information streaming into and out of that dimensionless point at the origin. Your arms, your legs, your memories, your age right down to the second, even the information that you HAVE a body is information streaming into that point NO FASTER than the speed of light.

    Now what this says to me is that if you were to go from rest up to light-speed, all that information would have to come with you. Basically, As you travel through space near the speed of light, all that information that makes up your body would propagate outward from your start-point at roughly the same speed. You would pretty much experience a freeze-frame of yourself until you stop, the same with your perceived spaceship... in other words, you would not experience any time! I feel like this is the fundamental aspect of time-dilation, unless there's a flaw in my logic.

    At this point I need to share another analogy which was explained to me on another forum by a physicist who I only know as "cavediver":

    The above excerpt is also very similar to Brian Greene's explanation.

    So, to say you are always travelling at the speed-of-light, just not always spatially, I have to assume that the origin of our personal worldline is what's doing the 'travelling' relative to everything else. If that's true and what I say is true then NOTHING ELSE is doing the travelling besides the dimensionless point at the origin of your worldline... not even your body!!! (if your bodily information was on the same vector through time as the worldline origin, then as above, you would experience a freeze-frame of yourself, which clearly we don't) This really would mean that what we experience is really 3-dimensional snapshots of a 4-dimensional universe (our BODIES would have to be 4-dimensional too!) In conclusion, depending on how much importance you place on my so called "worldline origin", I think intuitively it can shed some light on the shape, dimensionality, and biases of that troublesome little thing in physics we like to call "the observer".

    This is where I have to stop since to go further will make me sound crazy[er?]... comments? criticisms?
  2. jcsd
  3. May 14, 2008 #2
    Hi jdodger,

    I think you are making too much of the observer being a point particle which is just a mathematical convenience. Hope you do not mind if I start with a simple analogy. (it's my way of thinking, not dumbing down for you ;) The point particle at the origin is a zero dimensional object and has no independant existance. At a minimum we should should introduce one dimension of time for the observer. Just as a sea captain charts his progress on a map by drawing successive crosses on a map (rather than redrawing the map the every time) the relativistic observer who considers himself to be stationary looks at a clock in his hand and charts his progress through time by plotting successive crosses up the time axis of his space time chart. As cavediver mentions, no observer is truly stationary, so he does not remain at the origin. Now if we extend the observer to a 2 dimensional creature (one temporal dimension and one spatial dimension) with a spatial width of 1 unit then we could plot the head at origin (0,0) and the toe at (x,t) = (1,0) and a line joining the two points could represent the nervous system of the creature. One unit of time later the creatures brain is at (0,1) and the toe is at (1,1). Now a pain signal fom the toe to the brain would be represented by a diagonal line (at 45 degreees if the nervous system transmits at the speed of light) and where the diagonal line from the toe meets the brain is the time and place where the brain becomes aware of the the pain signal. When looked at like this, there is no freeze frame effect, just delays in communication from one part of the observer to another. Unless the observer is moving at the speed of light, it is always capable maintaining communicating between its various parts. Of course a brain that is a point particle is unlikely to be a functioning brain, so the two points of our creature could represent two cells within its brain connected by a nerve and so on.
  4. May 14, 2008 #3
    Isn't relativity violated without that 'mathematical convenience'?

    It's easy to miss this, so read closely... you're assuming the whole brain to be a discrete object which exists entirely at point (0,1). This is perfectly fine for every day purposes, however, the brain occupies *space*, therefore, unless you're ready to say that the brain is capable of non-local communication between it's different space-like separated parts, then you are REQUIRED to choose a dimensionless (or VERY VERY SMALL, I'm talkin' planck-length small) point of reference.

    Another subtle point: 'objects' may not necessarily remain at the origin when studying them, but the origin is special in that it is the only place that is both HERE and NOW. As an 'observer', not an object, are you ever ANYWHERE but "HERE" and "NOW"? The only claim I was making was that your PERSONAL worldline has no physical meaning for you unless you're always right at the origin.

    I probably shouldn't have used the term "freeze-frame". Naturally you do not notice any freeze-frame effect when travelling at near light speed... you INSTEAD experience time-dilation. What I meant by freeze frame is that if you were to reach the speed of light, ALL of your "bodily information" has to come with you... contained in that bodily information is your experience of time. So, the moment you jump to lightspeed, a light-wave from your body at the time you leave propagates outward at the same speed you're moving, so if you could somehow look out the window and see that lightwave, you would see just that one snapshot of when you left. When moving at near light speed time slows down because the information streaming into your personal worldline origin slows down (and of course you don't notice this 'slowing down' because even the act of 'noticing' has also slowed down). That lightwave isn't just a reflection of your body, it IS your body. Remember all the energy that makes up every atom in your body cannot travel faster than light.

    Now you're getting warmer... a brain that is a point particle is unlikely to be a functioning brain. The very experience of 'having' a functioning brain is information streaming into the origin, bound by the speed of light. Believe me, I know what a bold assertion that is, but what other choice do we have? Now don't ask me what is the 'nature' of this reference point, you can put it wherever you like! But let's face is, it's pretty much stuck to you! If you give it any dimension, you violate relativity (and/ or assign special powers to the observer), if you ignore it, then it kinda makes the rest of your light cone arbitrary. Anyway, you still may not agree with what I'm saying, but hopefully I've clarified my position and made you think a little bit. I am interested to hear any new comments/criticisms in light of my clarifications.
  5. May 15, 2008 #4


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    In relativity when we talk of an "observer", we use anthropomorphic words as if the observer were a human being. But, in terms of the theory, the observer is just a mathematical point.

    Real humans don't occupy a point in space, they occupy a 3D volume. In spacetime they occupy a 4D tube (with a 3D space cross-section), what you might call a "worldtube" (a name I just made up). If you break down a human being into component parts, each part, e.g. a neuron, has its own worldtube. All of the body's worldtubes are intertwined like strands of a rope to provide the composite "worldrope" of the whole body. And the interactions between the strands are limited by the speed of light.

    The origin of a coordinate system is just some arbitirary point you measure things from. It's convenient to label that point as "the observer", but you shouldn't confuse that point with a real human. A human's consciousness can't be localised to a zero-dimensional point; you could arbitarily choose any point as your origin -- for example the centre of mass is a convenient point you could choose if you like.

    The concept of a "now" is also a mathematical idealisation. Our human perception of "now" is somewhat vague and probably extends over many milliseconds. And what we perceive around us is what happened in the past, as the information takes time to reach us. We can never experience "now" directly, we can only calculate it retrospectively some time afterwards.

    Does any of that help?
  6. May 15, 2008 #5

    Yes, actually that does help a bit. First, it would be silly for me to claim that a human's consciousness could be localized to a zero dimensional point. I guess I was thinking of it more in terms of your consciousness merely having a 'point of reference' from which to base our experience of having arms and legs that can be said to be in a specific place at a specific time... it would have this point of reference even if the consciousness itself is spread out through the whole body, or even undefinable by our current ideas of 'location'. I thought I had an argument as to why that point of reference was necessary in order for the rest of our experience to be consistent... but you've made me question that.

    I guess what I'm still hung up on though is this: You're standing at rest, you've got on a wristwatch, heck this is even a special wristwatch, it sends signals to your brain at the speed of light telling it exactly how old the cells in your wrist are. For the sake of argument say you then instantly jump to the speed of light when your watch reads 4:00pm. Because that signal was en route to your brain, and because you've now matched speed with that signal, you're brain will never receive the signal until you come back to rest. To me that's *why* you experience time dilation. Pick any cell in your body and the same will be true, communication between cells, or even atoms if you like, will be delayed until you come to rest, hence the experience of time dilation. Would that mean that when moving close to the speed of light, light isn't "literally" travelling at speed 'c' relative to you, it's just an experiential bias, (albiet a very real bias that affects your age!)??
  7. May 15, 2008 #6
    One problem is that any physical object with rest mass can not move at the speed of light with respect to any other physical object. Moving close to the speed of light, for example moving at 0.9999999c, is still infinitely far away from moving at the speed of light. An observer never actually experiences his own time dilation. For him time seems to progress at the same rate of "one second per second" whatever his relative velocity to any other object.

    As for point masses there are any number of difficulties if they are taken literally not the least of which is infinite density. When analying the total volume of an object that is considered to made up off point masses then its total volume would be zero. Likewise the analysis of the slope of a curve can be estimated by analysing a small segment. The smaller the segment the greater the accuracy of the estimate, but once the segment becomes zero the answer becomes nonsense. The same goes for estimating the area under a curve. So in calculus the concept of the infinitesimal is introduced which is a very small but still non-zero. As you hinted at before, if a particle is at rest then the uncertainty principle tells us we can not be certain of the exactlocation of the particle. All the above indicates the concept of a point particle with zero volume is not really a physical possibility.
  8. May 15, 2008 #7
    Concerning the scenario given in post-1, how does a light signal (moving in the spatial dimension only) move between two objects (moving in the time dimension only), i.e. at rest?

    Concerning time dilation, the interactions at the atomic, molecular, biolgical, etc. level, are mediated by some form of light energy. The faster an object moves, the longer the time interval between interactions, because light speed is constant and independent of the moving source. If you are a biological system, then your rate of activity slows, meaning your perception and analysis of events, and sense of time.
    Hope this helps.
  9. May 16, 2008 #8
    YES, this is exactly what I was getting at, phrased another way. I suppose I should know better than to use hypothetical examples of people travelling *at* the speed of light... but essentially, "interactions at the atomic, molecular, biolgical, etc." are what you would "outrun" if you did somehow actually reach the speed of light which is why time slows down for you... because the "information" rate slows down. Would it be incorrect to then say that light doesn't "literally" travel at the same speed for all inertial frames, but it is only 'observed' to have the same speed due to what I have defined as the 'information rate' slowdown? There's three possibilities, a) I'm just wrong, b) there's really no difference between mine, and standard interpretations, c) what we think of as 'the passage of time' completely depends on a quantifiable amount of information being exchanged between points in spacetime.

    Any takers?

    On Kev's point,
    All I meant by "experiencing" time dilation, would be the observed effect that much more time has passed outside of your inertial reference frame.
  10. May 16, 2008 #9
    Just one more thing,
    Light travels through 'spacetime' not spatial dimension only... Of course there's also those claims of getting light to slow down to a complete stop in lab experiments. I suppose then light would be traveling through time only, at the speed of... Light! (not sure what the implications of that would be)
  11. May 16, 2008 #10


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    I don't think it's very helpful to think in terms of biology. Time dilation affects everything. It affects the quartz crystal in your watch. It affects the half-life of radioactive material. It is time itself that dilates.

    If we go back to the ruler example you gave in post #1, imagine each observer has their own ruler in spacetime; let's say it represents one nanosecond of time so it is one light-nanosecond long (conveniently about 30cm or 1 foot) in spacetime. The ruler is part of the observer's worldline.

    Two observers have their rulers pointing in slightly different directions, i.e. they are not travelling at the same speed. Each observer believes their own ruler is vertical and the other is tilted. Each observer measures time vertically upwards according to their own notion of "vertical" i.e. along their own ruler.

    Each observer measures their own ruler to be one light-ns tall (30 cm) but the other ruler to be slightly less tall (in the vertical direction). So the other observer's time appears to differ from their own time.

    The slight flaw in this analogy is that, due to the weird geometry of spacetime, when you take a vertical ruler and turn it through an angle, its vertical height actually increases, in spacetime geometry, instead of decreasing as you might think. In spacetime geometry, instead of Pythagoras' [itex]s^2 = x^2 + y^2[/itex], we have Minkowski's [itex]s^2 = c^2\,t^2 - x^2[/itex]. Here, s is the length of a ruler and ct is its vertical height. x is the distance travelled over the period of time the ruler represents.
  12. May 16, 2008 #11


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    you use the phrase

    'Now what this says to me is that if you were to go from rest up to light-speed, all that information would have to come with you.'

    It seems you have a notion of absolute velocity. Motion is relative. So right now I could be travelling at close to light-speed when viewed from some distant rapidly receeding star.

    When assigning velocities you should state from which frame of reference this velocity is measured.

    When it comes to measuring time in your own frame, you could use a clock, or a rat. They will both be equally affected by any time dilation effects, such as the twin scenario.

    See what I mean ? I'm always at rest in my own frame.

    I've got one of these watches. It sends a signal to me at light speed whenever I look at it. Amazing.

    Fine, since the watch is close to and stationary wrt to my wrist we may assume that time passes the same for the wrist and the watch.

    Whoa ! Now you've gone wrong. You cannot catch up with a light signal. The velocity of light is the same for all observers regardless of the relative velocities of the observer and receiver.

    You don't experience time dilation in your frame. Your clocks will tick at one second per second regardless of any relative velocity you might have wrt other frames.

    I repeat : You don't experience time dilation in your frame. Your clocks will tick at one second per second regardless of any relative velocity you might have wrt other frames.

    The other posters have been kind to you - there is no merit in anything you've proposed because you have not discovered the basic tenets of relativity. Sorry.

    Last edited: May 16, 2008
  13. May 16, 2008 #12
    Well ok, biology aside I was not trying to say that the effect was any different for quartz crystals or radioactive material. So when I say it is only an 'observed' effect, I guess what I mean is this: All time when you break it down is a measurement of motion against another measurement of motion, therefore, I don't think of time as an 'empty container' filled with 'stuff happening'. If you take away the stuff happening, there is no time. If you stretch out or compress the stuff happening, you dilate time. That's how I conceptualize it. My question is whether or not that disagree's with the 'accepted' interpretation, or does an 'accepted' interpretation even exist?
  14. May 16, 2008 #13
    The propagation speed of light in a vacuum is constant (c), and independent of its source.
    The result of the Michelson-Morley experiment supported the 2nd postulate 'the speed of light is the same for all observers'. The essence of the experiment, to detect an effect on the measured speed of light due to the hypothetical ether.

    The same amount of time (events) occurs for all of the universe. The clock of the moving observer runs at a slower rate, i.e. parses time into longer intervals. For a traveler to leave the earth and return, his total intervals will contain the same number of earth events as the clock total intervals on the earth. Inside his capsule, the rate of events slows. Outside his capsule, he sees a faster rate ahead or a slower rate behind. No one moves forward or backward in time.
    Also, because his mind slows with his clock, he is not aware of the different rate.
  15. May 16, 2008 #14
    Hello phyti.

    -----Inside his capsule, the rate of events slows.------

    The person inside the capsule experiences no change to his time.

    ----Outside his capsule, he sees a faster rate ahead or a slower rate behind. No one moves forward or backward in time.------

    This is an optical effect and has nothing to do with time dilation.

    The speed of light is the same in all inertial frames for all observers.

  16. May 18, 2008 #15
    That's what I said here:
    "Also, because his mind slows with his clock, he is not aware of the different rate."

    I'll be more precise. Inside his capsule, the rate of events slows, as observed from outside his capsule.

    If his time was not dilated, he would not see that 'optical effect'.
    His motion does not alter the occurence of events outside, and because his clock intervals are longer, he will record (on average) more 'outside' events in any interval.

    Most perception is optical effects, and because time dilation alters the moving observers perception, it has everything to do with what he experiences/perceives/sees.


    I see an object thrown into the air, slow to a stop and fall back to the ground.
    I would expect physics to explain what I saw and why, wouldn't you?
  17. May 18, 2008 #16


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    That disagrees very much with the accepted interpretation. You postulate some effect of absolute velocity that acts on matter and slows processes down. The point is that this effect is unobservable: nobody will ever observe time dilation himself, it always happens to other people. An unobservable cause for an unobservable effect is unacceptable. Try to adopt the accepted interpretation, which is that not a single property of an object itself changes physically with velocity, because velocity is a relative concept. All that changes with relative velocity is the relation of two objects, not the objects themselves. That's why it's called relativity.
    cavediver's explanation is, unfortunately, rather a non-standard visualisation which creates some problems if you carry it too far.
  18. May 18, 2008 #17
    If you research 'time dilation experiments', you can catch up.
    The most common: Hafele & Keating 1971 using cesium clocks,
    Rossi & Hall 1941 using muons,
    and Kaivila 1985 also using muons.
  19. May 18, 2008 #18
    I am sure when Ich said "The point is that this effect is unobservable: nobody will ever observe time dilation himself, it always happens to other people." he meant nobody measures time dilation of clocks at rest with themselves, only time dilation of clocks moving relative to them. For example in the twins experiment, at every point during the experiment both twins consider the clock of the other twin to be running slower than their own clock. At no point during the experiment before they are rejoin, does one twin measure that his own clock is time dilating relative to the other (even though it is). I am pretty sure Ich did not mean to imply that time dilation does not happen at all.
  20. May 19, 2008 #19
    Hmmm, Ok, well all that sounds about right, but it argues against a point I don't (think) I was making. I don't believe I implied any postulate of an effect of 'absolute' velocity'. One thing I said before was that because time can only be observed indirectly based upon the occurence of periodic events, i.e. the earth revolving around the sun, radioactive material decomposing, then I don't think time is an actual physical quantity, it's really just a quantity of some events measured against another event. As such, if you slow down communication between two points in space by accelerating the receiver away from the transmitter, then you've effectively dilated 'time'.

    Now this slowing down is achieved not by means of some absolute velocity, but by *accelerating away from your own inertial reference frame (the one you started at) thus slowing down communication between yourself in your NEW reference frame and your OLD reference frame. That's what I was illustrating with this example:

    Your wristwatch sends out a quick pulse of light to your eyes telling you what time it is... when that light pulse is halfway to your eyes, you IMMEDIATELY jump to the speed of light, therefore, that light pulse does not reach your eyes until you stop. from YOUR perspective, the light pulse reaches your eyes exactly when you'd expect it to, appearing to still travel at the speed of light even after you accelerated.

    The reason that you don't notice is because this same effect is happening between every atom in your body. Signals are en route, atomic and electrical forces between atoms and cells which control the speed of perception, and the speed of physical aging, even the quartz crystals in your watch. These signals became delayed not because of your absolute velocity, but because they originated in a *different inertial reference frame, that is to say, your ORIGINAL position before you accelerated. I use the example of IMMEDIATELY jumping from rest to lightspeed to really illustrate the effect, but I'm thinking it should be the same with gradual acceleration... the important aspect is the overall *change* in velocity.

    Can someone tell me where I'm going wrong?
  21. May 19, 2008 #20
    Here is something you are ovelooking. Let's define a metersecond as the time it takes light to travel one meter, for convenience. Now lets also say we have an observer with arms such that the signal path from his fingertips to his brain is one meter. A pinprick applied simultaneously to fingers on his left and right hands arrives simultaneously at his brain one meter second later. Now lets say just after the pinpricks are applied he is accelerated extremely quickly to 0.99c towards where his right hand initially was. The time for pain signal from his left hand will arrive at his brain much later than the signal from his right hand. Because he accelerated towards where his right hand was, the pain signal from his right hand takes much less than a metersecond according to an observer that remains in his original rest frame. Therefore, while the signal from his left hand is delayed the signal from his right hand is speeded up. Since both his left and right hands are part of his nervous system it is not correct to say all signals of an interconnected system are delayed and so it is not right to conclude is that time dilation is due a slow down of perception of signals, because we have shown that signals can speed up as well as slow down in the moving frame depending on direction.

    Second of all, it not right to conclude that time dilation is an illusion as result of the "speed of perception". This is clearly illustrated in the twins paradox. One baby twin is accelerated away at very high velocity while the other twin remains at rest and then the travelling twin turns around and returns at high speed. If the non-travelling twin is an old man with a walking stick and the returned twin is still a baby in a cot, then time dilation is not an illusion of perception or "speed of perception" but very real.

    That the twins paradox is true, is illustrated by actual observations of atmospheric muons and the fact that particles with very short lifetimes exist for much longer when stored at high velocity in laboratory experiments. In fact, the extension of particle lifetimes as measured in laboratories is in exact accord with the amount of time dilation predicted by Special and General Relativity.
    Last edited: May 19, 2008
  22. May 19, 2008 #21


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    Thanks kev, that is what I meant. Time dilation is a statement about the ralation of two bodies, not about the properties of the bodies themselves.
    You don't think so, but you did.
    That is completely irrelevant to time dilation. During acceleration, many effects have to be considered, most of them arising from the irregularily changing distances of certain (emission/reception-) events. But after finishing the acceleration phase, when all parts of this extended observer are stationary wrt each other again, there is no "slowing down" of signals or anything else. He is inertially moving again, just as before.
    That other observers see him time dilated has nothing to do with the acceleration phase, it is dependent of nothing else than the relative velocity of said observers. Accereation didn't change any property of the observer, he is equally right to claim to be at rest than before.
  23. May 19, 2008 #22
    Hmmm, well you all make convincing arguments, so at this point I think the original intent of my starting this thread has reached it's end so I personally don't have any further comments. I've learned that my imagination has evolved beyond my math skills to back it up, perhaps a sign it's time to go back and get that master's degree. :D
  24. May 19, 2008 #23
    You are close!

    If there is a physical entity for time, i.e. a process, regulation, synchronization,
    planck unit, etc., it hasn't been discovered yet.
    It's a relationship just as you mentioned, matching world events to a standard set of
    events (clock). It's a measurement process, like spatial measurement, because that's
    how science works, on the basis of measurement and comparison.

    What you describe here is changing the transmission time, or doppler effect due to
    motion between either, which the receiver/observer could detect, and is not dilation.

    Because the clock moves with the observer, and the clocks rate of periodic events
    depends on the motion, and his perception is altered in proportion to the clock, his
    'time' is subjective.
    SR enters the scene and translates one observers account of events to that of another,
    while preserving one set of events.
    If time dilation is the effect of light taking more 'time' to complete interactions,
    and the lengthening of the time intervals increases with speed, then the variable
    would be the speed of the observer compared to the speed of light. This is exactly the
    term (v/c)^2 used in the expression for time dilation.
    You use acceleration, but that is just change of speed, and SR applies to uniform linear motion (non acceleration, i.e. an inertial frame of reference).
    The simplest visual explanation I know of for time dilation is the light clock. It explains it in terms of physical processes.
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