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The Logic Behind Einstein's Relativity of Time

  1. Jan 7, 2006 #1
    This is my first post here. I have been trying to understand the logic behind the exclaimation that time is relative. To this moment I have failed.

    I guess I need some additional information in order to do this so I ask for your help.

    As it looks to me now Einstein has merely proven that relativity of time is a possibility, but not a fact.

    1. The speed at which physical objects operate is affected by circumstances.

    2. Time is measured by the speed at witch some defining physical objects operate.
    - - -

    3. Therefor time can be (and is) affected by circumstances.

    4. Time is relative.


    I think that 3 and 4 can not be derived from 1 and 2.

    Even if we accept that the measuring of time is relative, that doesn´t necessarily mean time itself is relative - does it?

    Time could very well be universal and constantly the same even though all time measuring devices start to behave differently.

    A crude example would be this.

    1. Temperature affects steel rods.

    2. The distance from Paris to Calais can be measured by using steel rods.
    - - -
    3. Therefor temperature can affect the measuring of the distance between Paris and Calais.

    4. The distance between Paris and Calais is relative.

    How is relativity of time different from this fallacy?

    Couldn't you deny that time was relative simply by saying that science has showed that clock can't measure time? (even though I doubt you had to go so far).
  2. jcsd
  3. Jan 7, 2006 #2


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    No scientific theory 'proves' anything. Relativity, like all scientific theories, is a model which is capable of making predictions. Since all of its predictions to date have matched with experiment, it seems the model is an accurate one.

    To note the relativity of time, you need only consider one thing: the constancy of the speed of light. If, as Einstein suggested, light always travels at the same speed, to all observers, then the relativity of time cannot be avoided.

    The idea that the speed of light may be constant to all observers was first noted in Maxwell's laws, which describe electromagnetic fields and radiation. These equations predict a specific speed of light, which in no way depends upon the movement of any observer -- quite contrary to everything in Newtonian physics.

    If Maxwell's equations are right (and I'd say they are, considering they are used very heavily in the design of every electronic device), then the speed of light must be constant for all observers. If the speed of light (or any other thing) is constant for all observers, it follows directly that time cannot be constant for all observers.

    - Warren
  4. Jan 7, 2006 #3
    Thanks for a quick and informed reply.

    I, however, fail to grasp the logical connection between the speed of light being constant and time being relative.

    Would you please clarify?

    I understand that if you define time as being "that which clocks measure" then time must be relative. But that is neither brilliant nor important. You would simply be assuming that which you wanted to prove (and surely all of science has very much do do with proofs).
  5. Jan 7, 2006 #4


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    If some speed c is constant for all observers, even those in arbitrary relative velocity with respect to each other, then time cannot be absolute for all observers. If you'd like me to show this mathematically, I can -- but I suspect you're looking to discuss philosophy here.

    Do you have some better concept of time than "that which clocks measure?" Can your concept also be used in an experiment?

    - Warren
  6. Jan 7, 2006 #5


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    That's incorrect!

    Recall that before relativity, people used to treat time as some absolute thing, and would spend a lot of effort trying to explain why clocks would fail to measure time correctly.

    At that time, this apparently simple notion that time is simply what a clock measures was a brilliant and important idea. (Even today, despite relativity having existed for over a century, we still see how difficult it is for some people to grasp this idea)
  7. Jan 7, 2006 #6
    Again, thanks for very good answers.

    Hurkyl: What I ment is that if one is looking for a "proof" of the relativity of time, it would neither be brilliant nor important to plainly assume that something we know to be relative is time.

    chroot: I am merely thinking along those lines: Does the "old" concept of time, of time being something constant and everywhere the same, necessarily contradict the physical evidence of relativity.

    I ask you to please be patient whith me, I would like nothing more than to understand this.

    Let's say that two men wanted to measure the speed of light, both with the same type of clocks.

    They put up two posts (A and B) and know that it should take the light 60 seconds to travel from A to B.

    Let's say that they know the exact moment light passes (or is originated) in A and that is when they start their clocks.

    One of them now stands absolutely still but the other travels in circles at great speed for 55 seconds.

    Then he stops and stands next to the other man.

    Now, time being that which cocks measure, and speed being distance / time would they both calculate the same speed of light?

    If not, what is wrong with this picture. Could we say that one man had the wrong time?
  8. Jan 7, 2006 #7

    Tom Mattson

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    The relativity of time isn't assumed by the postulates of relativity. It is derived from them. You seemed to grasp this yourself in the opening post, in which you did not consider the relativity of time to be a premise of the argument.

    The old concept of time does indeed contradict experimental evidence. See the following website, especially Section 4.


    OK, but I think you're going to have to abandon your attempt to reduce the theory of relativity to a simple syllogism. If you leave out the mathematics, all of the logical deductions that lead from the postulates of relativity to time dilation are completely hidden.

    Here is Einstein's original paper, which I strongly recommend you read.


    60 seconds in which frame? One of the things that relativity has taught us is that we cannot take it for granted that all inertial observers will agree on the time.

    Yes, the local speed of light will be the same for both observers. It would help matters if you kept it simple though. You have one observer who is non-inertial (the one chasing his tail). Why not have the moving observer traveling in a straight line at constant speed? Relativistic effects would still be present, and we wouldn't have the nasty acceleration to account for.

    You could not say that if both clocks are functioning properly.
  9. Jan 8, 2006 #8
    I think we are not exactly on the same page here. I have absolutely no reason to think that the math of Einstein is faulty in any way. I just cant see that the findings (to the extent I understand them) contradict an concept of universal time.

    Let's imagine that the material world simply didn´t have the ability to let anything pass through it faster than c. It would be a symptom of this particular world and nothing else, we could easily imagine a world with speeds upto 1.000.000.c.

    Another aspect of this world is that material things tend to work more slowly as they go faster.

    Everything above has to do with the way material (and vacum being part of that) behave in this world but not with time which is constant and universal.

    There is a phenomena in this world called light. The energy of light is so great that it could possibly travel much faster than c if it wasn´t for the limitations of it's circumstances in this particular setting.

    It doesn´t matter how fast you go relative to the light you will never be able to see it go more slowly than this worlds maximum speed.

    It would still be light any way you look at it. The only difference would be in frequency of the light which could vary according to your relative speeds (we wouldn't even have to allow that).

    Time could well be universal in the abovementioned circumstances. The only thing which is relative about time is the fact that no one would be able to measure it correctly.

    Now in what way would such a world be impossible and inefficient in explaining the things relativity explains?

    Would such a world be more complicated than Einstein's model?

    Or would it perhaps differ in the sense that universal time has become a possibility instead of necessity, and therefor is taken out of Einstein's description?
  10. Jan 8, 2006 #9


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    Do you have any interest in learning about relativity (you seem to have some grave misconceptions), or do you simply want to debate strawman arguments?

    - Warren
  11. Jan 8, 2006 #10

    matt grime

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    Postulate: the speed of light (in a vacuum) is constant in all inertial frames. Deduction: time is a relative concept.

    *Experimental* evidence, which as near to proof as one can hope for in physics, that the assumption that the speed of light is constant is reasonable exists, and therefore is evidence that time is relative dependent on the inertial frame.

    What is troubling you about that? (note if you're rejecting all the postulates and definitions then you are arguing about something else entirely and 'we don't care' in some sense, since you are not discussing the issues as they are defined by anyone else).
  12. Jan 8, 2006 #11
    We could look at your question from different logic viewpoints:

    1. Einstein made many important points about time, so did Einstein prove time is relative? Did he prove this in his paper, formulas, or general thinking? I would say forget his paper and his formulas for an absolute view on this. Einstein wrote two major relativity theories and papers, but it appears he had a change of heart later in life on some of the issues. Here is what many believe Einstein came to understand:

    a. There is a type of gravitationally modified absolute space continuum which matter and light travels in reference to.
    b. Light for example travels at exactly the same speed relative to this absolute space continuum in the absence of gravity, if you could measure it in absolute terms, but we can't.
    c. Observers can't tell whether they are moving relative to the absolute space continuum as their measuring tools are always skewed. Same goes for observers trying to measure their speed. All clocks are skewed when traveling in relation to the space continuum.
    d. Because all clocks and any measuring systems are always skewed, there is no such thing as absolute time, and all time can be considered to be relative.

    2. Who really cares about what Einstein said, is time really relative, based on our latest scientific knowledge? Here is a more modern interpretation of what we know about relative time.

    a. Einstein appears to be largely right about our measuring systems being relative, including time. But he may have led people astray by focusing on time being part of the 4 dimensional space time continuum. We can actually calculate relative time in many different ways.
    b. Though different observers will all measure time differently, we can establish a quasi absolute time system. By using astronomical observations, multiple calculations, and theory, we can establish a time based on say that the space continuum might be stationary with respect to us. This won't yield accurate results at near the speed of light, but it's better than nothing. It's what we are using often for many modern physics calculations.

    3. If time is even a little bit relative, do we define time as being relative? Yes I think so. Even if we use a quasi absolute time system. But we should define what kind of relative time system we are using.

    4. What do we mean by time being relative? Can we define time as being relative because we can never calculate it absolutely? It would say yes. This question has a lot of implications though. For example did Einstein believe that because observers measure time differently that we can go back in time? Do we believe that? I'll leave this one open because we could go on and on.

    What do you think?
    Last edited: Jan 8, 2006
  13. Jan 8, 2006 #12


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    Virtually everything you just said is hocus-pocus. Einstein never said any of things you claim he said, either directly or indirectly. In addition to misquoting Einstein, it also seems you have a few very grave misconceptions about how relativity works. Such speculative posts are not welcome here.

    - Warren
  14. Jan 8, 2006 #13
    Well I don't think it's fair to hang someone without a fair trial. Pick something or a few things you have issue with, and I'll respond.
  15. Jan 9, 2006 #14
    I am a bit surprised by the aggressive tone of some of the replies. This is hardly a place of worship, it is a place for throwing around ideas, clarifying some difficult things for some (such as myself) and throw about some of the most marvelous things about the world we live in.

    However, I would like to thank you all for your answers and I take it as sign of respect and patience. I really appreciate it and hope you will guide me further.

    All I am saying is this: Given that the laws of physics are the same to everyone and everyone experiences the speed of light as being the same it is obvious that time, being that which clock measure, is relative.

    However I can not see that this is the only possible idea of time. Given that clocks certainly can slow down when time doesn´t why couldn´t time still be one when the material of the clocks and yourself changes?

    But surely I don't see the whole picture and there is a lot I don´t know. That is why I am here.

    Now just one question before things get all hot again:

    According to the theory of relativity size of a thing moving relative to you shrinks (from your viewpoint).

    I seem to have heard something about two airoplanes meeting both being relatively smaller than the other.

    What would happen if you approached me at great speed (relative to me) and I saw you as both "ticking" slower and being smaller. Just as we meet I would lower a hoop and you would fly through it at this great speed (or I would "catch" you from your point of view).

    Seen from my point of view the diameter of the hoop is much greather than that of your airoplane.

    Seen from your point of view the hoop is much smaller than the plane.

    Seen from the point of view of someone standing below the point where we meet the hoop and the plane are of exactly the same size.

    Now, what happens?
  16. Jan 9, 2006 #15

    Tom Mattson

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    Since I've already had this conversation many times before, I am going to borrow my own words from a thread at Science Forums Network:

    [URL [Broken]
    Does time go faster for an object moving faster?[/url]

    In response to the question of whether time itself really slows down, or do the clocks merely slow down while time passes normally:

    What's the difference? There are no indicators of time other than clocks. And if all clocks--regardless of the mechanism by which they work--all show the exact same lag in elapsed time when subjected to "twin-paradox" type experiments, then in what sense can it be said that time dilation has not occured? Or should we suppose that the clocks are all conspiring to play a trick on us?

    And in response to the question of whether the famous "twins" would be affected in the same way as atomic clocks:

    It would have to be done with actual human beings before we could say for sure. What we do know is that atomic and subatomic clocks that operate according to the electromagnetic, weak, and strong interactions show relativistic effects. If we had as precise a clock that were based on the gravitational interaction and tested it, then we would have covered all the bases.

    So the answer to your question above is: There is presently no reason to think that the effects would be different.

    And in summary:

    I asked it once before, now I'm asking again: What's the difference?

    What can you point to, apart from the "effects of time", that is this thing called "time"? Nothing, that's what. So if all experiments designed to test the so-called "effects of time" conform to the predictions of SR, then there simply is nothing you can point to and say, "Ah, but this hasn't been affected!"

    That pretty much sums it up. If every conceivable indicator of time matches the predictions of relativity regardless of the mechanism by which it works, then the "absolute time" adherent simply has no refuge left. As has been noted before, scientific evidence doesn't prove that time is relative. As with any wrong idea in science, the death of absolute time is brought about one cut at a time.
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  17. Jan 9, 2006 #16
    So we are basically down to this question: Does Einstein's relativity render the concept of "absolut time" useless?

    Perhaps it does.

    As I said in my original post I really can see that relativity of time is possible but I don´t see how all other possibilities (including the one with universal idea of time) can be excluded.

    Now, my background is philosophy, not physics. And perhaps that is where my problem lies. For I can't get out of thinking in these terms:

    1. If relativity is correct it will explain many observations made or still waiting to be made.

    2. It does explain them.

    Therefor relativity is correct.

    Now this is a fallacy.

    A -> B

    As many of you have pointed out physics tend to ease up on the "proof" bit of things and measure the "truthfulness" of ideas against some other measure stick.

    However, I can not see that such pragmatic points of view really justify the passion and the affect of the quest for the truth.

    It wasn´t merely wanting to be useful that drowe Galileio, Copernicus and Einstein. It was wanting to be right.

    But it seems to me that perhaps the only thing they can ultimately take pride in is proving someone else wrong.

    Then again, I don´t know enough about physics to be able to state that

    A -> B

    is followed by

    C -> B

    and even

    C -> ~A

    and then even if we have


    we can't even state

    A v C

    But we can deny both




    as the ultimate answer.

    I just ask you to remember I am primarily thinking about the logic behind Einstein's relativity (as shown in the title and my choosing of Philosophy)

    My question is, if we accept this form:

    A -> B
    and C is the idea of Universal time

    Can we show that

    C -> ~B

    and therefor assume that since


    C is not a possibility.
  18. Jan 9, 2006 #17

    Tom Mattson

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    A theory cannot render a concept useless. Only experimental evidence can do that. What theories can do is either affirm or deny concepts.

    Relativity uniquivocally denies absolute time.

    If you accept the postulates of relativity then relative time can be deduced from those postulates, and absolute time is excluded. If you deny the postulates of relativity then anything is possible. Since you are interested in the logic of the relativity of time, I was under the assumption that you were accepting the postulates of relativity. Is that the case?

    I think you might need to study more philosophy then, because in any introductory course in the philosophy of science you would have learned that science does not proceed by purely deductive reasoning. It cannot, because science is done a posteriori.

    Where to begin?

    First of all, your misconception here has nothing to do with relativity and everything to do with the rudiments of the philosophy of science. It is well known that the justification of scientific theories is done inductively. As has been noted, scientific theories are never proven.

    And second, your argument above really doesn't address what I thought you were getting at with your first post, which is the chain of deductions that leads one from the postulates of relativity to the concept of absolute time. I already mentioned that you aren't going to get there with these simple syllogisms. If you don't look at the mathematics then the chain of reasoning is completely hidden.

    I don't have either the time or the energy to teach a course in the philosophy of science here, but a major breakthrough in that field came in the 1930's with Popper's concept of falsifiability, which he introduced in his book The Logic of Scientific Discovery. A few of us discussed it in the following thread:

    "Falsifiability" - has it been fully discredited?

    And I discussed it (as "Tommy Boy") at Philosophy Forums in a thread called Paradox of the ravens, wherein I argued that falsifiability solves Hempel's famous paradox. The paradox has been discussed more recently in a new thread of the same title, and the formal logic is developed more explicitly.
    Last edited: Jan 9, 2006
  19. Jan 9, 2006 #18

    matt grime

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    that's science: put up or shut up. a sadly masculine way of debating but it's evolved that way. personally i found the arts subjects to be far more cut throat since at least in science it is perfectly possible for two people to have differing views and be able to support them by solid objective evidence whereas the more opinion-based subjects tend to simply go in for attacks on people's views based upon subjective interpretation.

    who is saying that it is 'the only concept'? we don't use relativistic mechanics on the quantum scale. if you find a good explanation of quantum gravity i'm sure there are a lot of people would be keen to hear it.

    It is the best concept we have (at large scales) and it is one backed by a huge amount of ever increasing data and evidence. since any attempt to add in extra (unverifiable) assumptions about there being some alleged ambient space in which out space-time exists and in which different laws of physics apply merely adds complexity and not expository power then we can reject these assumptions as being useless to us.
    Last edited: Jan 9, 2006
  20. Jan 9, 2006 #19

    Okay, stepping back for a sec, best I can find the speed of light is 299 792 458 m / s.

    I have no reason, or experience, to doubt that.

    But here's what I don't understand:

    Why is it this number and not any other number?

    Does the shape, construction, or composition of the universe control what the speed of light is?

    or is 299 792 458 m / s simply a number that we know is true, but, as far as we currently understand, is without a prior cause or reason?

    Basically, is the speed of light just plain IS, or is the speed of light IS BECAUSE?

  21. Jan 9, 2006 #20


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    Nothing that we know of so far constrains the speed of light to be one number rather than another. It is an unexplained parameter, one of about 40 or so.
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