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If light itself it timeless?

  1. Jul 3, 2010 #1
    If light is timeless (photons), then doesn't that mean that everything we see is just 13.7 billion year old light?
  2. jcsd
  3. Jul 3, 2010 #2
    Light is not "timeless". Your mistaking a perspective dependent sense of a sequence of events as something that has absolute meaning independent of your perspective.
  4. Jul 5, 2010 #3
    Where did you get the idea that photons were timeless? And your conclusion indicates that's not what you believe.
  5. Jul 5, 2010 #4


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    Science Advisor

    Light doesn't age. It's proper time is always a constant, because it moves along null-geodesics.

    That means from perspective of light, it's emission and absorption happen at the same time. It doesn't mean all light is the age of the universe. That right there is a strange leap of logic.
  6. Jul 5, 2010 #5


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    Staff: Mentor

    Right: it would be closer to reality to say that all light has an age of 0.
  7. Jul 6, 2010 #6
    It depends entirely on what you regard as time.
    Space is time and time is space.

    From one person's point of view a parsec is a parsec. From someone else's it could be a couple of days.

    You can't talk about the age of light any more than you can talk about it's length.
  8. Jul 6, 2010 #7
    Here's an easy way to understand it: from the photon's reference frame, the time between emission and absorption is 0, but from our frame of reference, this is clearly not the case. Light emitted 13 billion years ago (cosmic background microwaves) and light emitted from your computer screen about a nanosecond ago (From memory/really rough estimation, It seems that it should take about one nanosecond for the light coming from your computer to reach your eye), from the perspective of the photon, exists for the same duration, namely zero duration. Now, from our reference frame, they take vastly different amounts of time. Now, if you moved with the photon at a speed really close to its speed, the closer both 13 billion years and one nanosecond would be to each other, and to zero. Your speed in space affects your speed in time.
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