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Thread: Relativity

  1. #1 Relativity 
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    Dear friends,

    In the relativity experiments measuring the time in two inertial frames, it is stated that a clock using the principles of light is used. That is why we obtained the difference in two inertial frames. If we use an ordinary clock (eg. using quartz), do we obtain the same result?


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  3. #2  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Simple answer, no.

    Light is effected by time dilation, just not in the same way as other things. It still travels at light speed, but the wavelength changes.


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  4. #3  
    Moderator Moderator Dishmaster's Avatar
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    Quote Originally Posted by MagiMaster
    Simple answer, no.

    Light is effected by time dilation, just not in the same way as other things. It still travels at light speed, but the wavelength changes.
    Are you sure? A light clock is usually used in thought experiments, because it is not affected by mechanical inaccuracies. It only measures the time that passes for a photon passing the way between the light source and a mirror that reflects it. Here is a visualisation of such an experiment.

    http://galileoandeinstein.physics.vi...lightclock.swf

    Such an experimental setup only measures the time. So, it should - in principle - be independent of the clock that is used. The results should be the same.

    You are right that the speed of light is the same irrespective of the reference frame. But this is exactly, what is used to measure time in any reference frame from which this clock is observed. The wavelength shift is only observed, if both velocities (light and light source/detector) have a common vector component. This is not the case for the light clock.
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  5. #4  
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    Sir,
    My doubt is suppose two men, one travel in a space vehicle travelling with high speed comparable with that of light and the second man is on ground. Two men have the same clock that we usually using in our homes. Then does the time shown by the clocks in two inertial frames are different?
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  6. #5  
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    Quote Originally Posted by Sreeja
    Sir,
    My doubt is suppose two men, one travel in a space vehicle travelling with high speed comparable with that of light and the second man is on ground. Two men have the same clock that we usually using in our homes. Then does the time shown by the clocks in two inertial frames are different?
    It depends on who is looking. The guy, who is travelling with the clock will not notice anything. But if the one on the ground defined as the rest frame would be able to see the clock of the other guy, he would notice that that clock runs slower than his own. The other problem is that according to relativity, it is not possible to define an observation of two incidents (the two clocks) as synchronous. It strongly depends on the state of the observer. What seems to happen at the same time for one observer, is not necessarily happening at the same time for another.
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  7. #6  
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    I think we do see the same result.





    Is the equation for time dilation and makes no referencce to what kind of clock you use. Also atomic clocks have been used to test this. (Although I realise these use microwave radiation.)
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  8. #7  
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    Quote Originally Posted by Stuart Thomson
    I think we do see the same result.





    Is the equation for time dilation and makes no referencce to what kind of clock you use. Also atomic clocks have been used to test this. (Although I realise these use microwave radiation.)
    Indeed, the one "travelling" will see the same impact on the clock of the "resting" guy like the "resting" man is seeing on the clock of the "traveller". This is a result of the fundamental principles in relativity. All reference frames are alike. But as soon as one of those is comparing the two clocks, he will see a difference. And it's the same for both.
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  9. #8  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Microwaves are still EM radiation and travel at light speed. Also, to make a clock out of anything, you need something periodic. With light, there are two possibilities. Eith you measure how often a photon is emitted, or you measure the frequency of the beam of light. In either case, time dilation will effect these numbers the same as any other periodic event. Note though that the light still travels at light speed.
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  10. #9  
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    Quote Originally Posted by Dishmaster
    Quote Originally Posted by Stuart Thomson
    I think we do see the same result.





    Is the equation for time dilation and makes no referencce to what kind of clock you use. Also atomic clocks have been used to test this. (Although I realise these use microwave radiation.)
    Indeed, the one "travelling" will see the same impact on the clock of the "resting" guy like the "resting" man is seeing on the clock of the "traveller". This is a result of the fundamental principles in relativity. All reference frames are alike. But as soon as one of those is comparing the two clocks, he will see a difference. And it's the same for both.
    All inertial frames 8) :P

    Quote Originally Posted by MagiMaster
    Microwaves are still EM radiation and travel at light speed. Also, to make a clock out of anything, you need something periodic. With light, there are two possibilities. Eith you measure how often a photon is emitted, or you measure the frequency of the beam of light. In either case, time dilation will effect these numbers the same as any other periodic event. Note though that the light still travels at light speed.
    It would work reagrdless of the type of clock used I think. For example in the muon experiment that confirmed time dilation, where is the light clock there? It is the muon's 'internal' clock that feels the effect.[/quote]
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  11. #10 Re: Relativity 
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    Quote Originally Posted by Sreeja
    Dear friends,

    In the relativity experiments measuring the time in two inertial frames, it is stated that a clock using the principles of light is used. That is why we obtained the difference in two inertial frames. If we use an ordinary clock (eg. using quartz), do we obtain the same result?
    The experiment has been using two atomic clocks and flying one around on an airplane. The time difference predicted by relativity was seen in the experiment. Another confirmation of relativity.
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