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Explaining time dilation from length contraction easier

  1. Feb 11, 2012 #1
    For the explanation of the Lorentz derivation in Wiki with the known triangle, 2 rest frames are considered in 1 view, so that's not forbidden. So I do too.

    To explain time dilation is easier to understand if you see it by length contraction. That could be explained somehow in the future, because length is real to understand ...

    If you P move with speed V in rest frame A, somebody in rest frame A takes your time t between a start and endpoint (distance X m). P takes his rolling ruler with him and a clock (in rest frame B), and stops the clock after distance X (for him). His clock (smaller) had stopped after 1/γ . X m. So there is nothing special about time because his clock stopped after 1/γ . t, it's just the difference in equal moments, that must be corrected in calculations.

    Maybe I say it too simple as I did many times before ...
  2. jcsd
  3. Feb 16, 2012 #2
    Suddenly I begin it to understand Relativity, it goes about Simultaneity.

    So one considers the moments t in frame A en 1/γ . t simultaneously because of the length contraction from our unit meter in frame A. So in the old meter the car is on t in frame A and with the new smaller unit meter (1/γ) the car is in frame A on 1/γ . t (but also in frame B where the car is standing still).

    So duration is everywhere the same, there is nothing strange about time in the SR, I have not read GR so maybe there is something different in duration ?

    Right ? It's just the length contraction !

    If this is true I can't understand why I have not understand this in books all that time ... on my own website I can sure explain this more simple than, if this is right ?
  4. Feb 16, 2012 #3


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    The length contraction occurs only along the direction of motion and yet there is time dilation for a light clock where the light bounces back and forth at right angles to the direction of motion. When you rotate the light clock so that the light bounces back and forth along the direction of motion, the mirrors have to come closer together in order to tick at the same rate. So it cannot just be the length contraction, can it?

    This topic recently came up in another thread called Conflicting clocks. Why don't you take a look at that thread and see if it makes sense to you?
  5. Feb 16, 2012 #4
    Hi Ghwellsjr,

    Yes you mean the known triangle for the short Lorentz derivation.

    But I have problems with this situation, of course it can be true and than I should understand, but that's the point. I would like to believe in time dilation and should be really interesting for me, but I am not that far ...

    I mentioned this in my first blog last alinea's, maybe you would have a good answer it helps me .. it is after the second last "====================" ..
  6. Feb 17, 2012 #5


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    Why should I pursue this any farther on your blog when you reject what I'm offering here? I get the impression you didn't even read my post. You didn't respond to anything I said. I didn't say anything about Lorentz derivation. You always want to reject the simple explanations and come up with your own.

    Please answer my question in the previous post: how can you explain time dilation as being nothing more than length contraction when length contraction only applies along the direction of motion whereas time dilation applies without regard to the direction of motion?
  7. Feb 17, 2012 #6
    Hi Ghwellsjr,

    Thanks for the answer, interesting.

    Sorry for that, but it was a quick answer for me, I had to go sleeping.

    Now again, so I wanted always answer later.

    But I can already give a quick answer (I come back later on it in the weekend).

    Your situation is mine with the car but with light in an angel right on the car's top. If I don't believe in time dilation there is nothing special for me in your example. In both cases the clock has the same rate but specifies a different time because its light path is shorter.

    But you can also ask, why can I explain in the moving direction with length contraction and so a shorter meter (1/γ) the same time 1/γ.t with and without time dilation (Lorentz) ? Just as you always say "you need a clock to measure time", so I say "you need a ruler to measure a distance" ...

    I go also to look to your other example later ..
  8. Feb 18, 2012 #7


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    If you don't believe in time dilation, then why are you trying to explain it with just length contraction?
    How can a clock have the same rate yet specify a different time? Don't you understand that an observer traveling with the clock will use the flashes of light bouncing off a mirror as a basis for time? If he has two clocks at right angles to each other and the light bounces at a different rate for one of them than for the other one, then he's going to have a device that will detect absolute motion. Is that what you are promoting? And it doesn't matter if it is a light clock--any clock will behave the same way.
    If light only has to travel a shorter distance, wouldn't that mean the clock was ticking more rapidly?
    I didn't say either one of those things--Einstein did. And you should read what he wrote and try to understand it and believe it instead of trying to work these things out on your own.

    Why don't you start with his 1905 paper introducing Special Relativity? In section 1, you will see where he talked about defining distance with a rigid ruler:
    Following that, he goes on to talk about the definition of time, both local and remote.

    I really don't want to discuss your personal ideas about these things but I would be happy to help you understand what Einstein said about them. Do you want to give up on trying to explain these things better than Einstein did and learn what he had to say?
  9. Feb 19, 2012 #8
    Thanks for the answers Ghwellsjr.

    I answered to quick last time, and removed that answer, so now I take the time for it, it needed for this subject.

    I realise already that I gave the wrong answer, it is what you said, when a shorter distance it will bounce more rapidly. I proved in my blogs that I did understand this already.

    Somewhere I am more happy now because I understand time dilation completely in the moving direction, I had a wrong understanding from time dilation since the beginning, that's when you learn it on your own. There is no different duration, in the moving direction it's takes just lesser time because the unit meter is smaller (all objects are smaller in length). It are the times where my car is in frame A and B because of a different unit meter, the difference (1 - 1/γ) is the time you "loose", so no secret at all anymore. Its just the path of a light wave because of the smaller length.

    In fact I saw it from the beginning right (you know my first topic) where I said consider light as the time (there I started my interest with my idea to see if I was right), I mean now see it as the constant ration C (distance / time) presented by light in space but not on earth (than it is just that ration C).

    That this ration C is always constant (measured when you move) is no surprise for me (I said so in my blog) and can understand that very well.

    In this way I can indeed it explain very simple on my website, more than I already have done. I find this all very bad explained in books generally, in fact it is easy and logically. Average people don't need to know all details, but slower gong time is difficult for people while it is not. I did try this out on my sister and she understand it now easily. I analysed this now to the bottom for myself on my own.

    BUT like you said, in other directions you have also the same time dilation seen from my car in frame B. And in this other directions the unit meter is equal as in frame A, where lies the border of length contraction ...

    This can mean for me:
    1) there is no time dilation, it is just the ration C again, and so time is not different (because the unit meter is as in frame A, no length contraction)
    2) there is length contraction in all directions (as I suggest in my blog) and can be the reason if there is really time dilation as well

    I am curious what you think, why could one it easily explain in the moving direction and why would it be mysterious in other directions ? Not all have to be right what Einstein says, extended theories will be possible in the future. In my blogs it are only my ideas, I have not read all of Einstein, it is just an idea, we will see in the future what will be the right explanation, but I guess never mysteries ... maybe Lorentz is a start maybe there is another formula closer to the truth ...
  10. Feb 21, 2012 #9
    There is a difference with my first thought in my first topic, a light wave need not to be smaller when you move (follow a photon in thought in the other frame), but it is you because of length contraction (for a person width).

    But in my new thoughts that all have to go smaller, a light wave's amplitude too (or another electromagnetic wave), otherwise its amplitude is not in ration and that's not logically. If it is in only one direction, length contraction, the amplitude have not be changed from a light wave in the same direction.
  11. Feb 22, 2012 #10
    Can somebody help me in this example what I see wrong, only in the moving direction (ignore the other directions for the moment), than I am maybe very close to understanding ? Is the car not already smaller when measuring in frame A? What does it mean the car is on distance 1/γ . X or 1/γ . t in frame B compared to the starting point in frame A because of length contraction? This example can happens in front of your eyes, you see the driver but he experiences it different. What exactly if you see this 2 frames in one view with geometry like in the short derivation of Lorentz was used? I am willing to look to these things different, so how have you to look in this easy example? Please explain ... and I will be convinced before I give up ...
    Last edited: Feb 22, 2012
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