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Light slow downs during long journeys?

  1. Aug 7, 2009 #1


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    Is it true? I've heard this news couple years ago: Not for the short distances but during long distance travels light slow downs once in a while. İt sounds logical to me, we shouldn't expect the light will move at the same speed all the times and everywhere. During it's billions of years travel it's speed might drop a little bit every once in a while. I remember this was a british based study but I'm not sure. Anybody knows more about this subject? Thanks in advance.
  2. jcsd
  3. Aug 7, 2009 #2


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    No, the speed of light in vacuum is a constant. You may be misremembering the cosmological redshift: because of the expansion of the universe, distant galaxies are moving faster away from us than nearer ones, so their light is more heavily redshifted. This would mean that if you communicate with aliens on a far-away planet, those aliens would see photons of lower frequency and energy than someone on Earth. However, the aliens' measurements would give the same answer for the speed of light: 300 000 km/s (but in whatever units they use).
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