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An example of moving towards a light source

  1. Aug 11, 2010 #1

    I've a question that I'll illustrate by presenting the following example:

    Let's imagine Einstein in a car that's moving away from a clock. This clock 'send' a light beam with the information 'It's 12 o'clock'. If the velocity of this car is close to c, I understand that Einstein will be driving beside the light beam, therefore beside the information, always seeing that the time is 12 o'clock, no changes. But, and this is my question, if Einstein drives towards the clock (close to c, too), will he see the events accelerated on the reference system of the clock (-earth)? why? I mean, einstein's only moving to the light: the only thing that he'll notice is that the information of '12 o'clock' will arrive earlier to his eyes...

  2. jcsd
  3. Aug 11, 2010 #2


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    Re: An example of moving towards al light source

    Hi atomqwerty, welcome to PF!

    What you're describing is the http://en.wikipedia.org/wiki/Doppler_effect" [Broken]. You see the clock faster or slower, depending on direction.
    Only after you correct for the light travel times, you conclude that the clock ticks slower from your perspective. This is time dilation, and independent of direction.
    Last edited by a moderator: May 4, 2017
  4. Aug 11, 2010 #3
    Thank you, Ich :)
    You mentioned the Doppler effect and if that effect only implies a change of the wavelenght that comes from a source of light (em field) or sound, would you see, for example, that the red color of a traffic light has turned into a green light if you'd drive at a huge speed?
  5. Aug 11, 2010 #4


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    Actually, that was an exercise in my relativity textbook in school. The driver got away without a ticket, IIRC.
  6. Aug 11, 2010 #5
    .(for ignoring lights) but got a huge one for speeding
  7. Aug 12, 2010 #6
    Hahaha! :D
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