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How long can a light ray travel

  1. May 29, 2010 #1
    I was wondering and have looked for a while on the internet to find out, in the end i found this site so i made an account.

    Can anyone tell me if light rays from stars fade out over time or if they travel for an infinite ammount of time. Incase im not clear enough, im asking if light rays lose energy as they travel and so does that mean that there is a limit to how far a light ray can travel, or can it go on forever
  2. jcsd
  3. May 29, 2010 #2
    If there is nothing in its way to absorb a photon, it will travel forever.
  4. May 29, 2010 #3
    The only way it will lose energy is interaction with other particles.

    So it can travel in a vacuum indefinitely.

  5. May 29, 2010 #4


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    Gold Member

    Not quite true. Gravitational redshift and redshift due to cosmological expansion will cause it to lose energy.

    Losing energy means it is redshifted; a photons in the visible light spectrum might redshift down to microwave mengths or radio lengths.

    However, this, in itself, will not end or impede its travel though the universe cause it to get lost. It is possible in theory for it to travel forever, redshifting as it goes.

    We are currently observing light rays that have been traveling for 13 billion years.
  6. May 30, 2010 #5
    thanks guys been helpful
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