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B Does speed of light change?

  1. Aug 16, 2016 #1
    Light travels more slowly through light-transmitting substances such as air or glass, otherwise no lens would refract light. so does this mean that the speed of light is not a universal constant?
  2. jcsd
  3. Aug 16, 2016 #2
    Yes, the speed of light in various media is not a universal constant.
  4. Aug 16, 2016 #3
    The universal constant is the speed of light in a vacuum
  5. Aug 16, 2016 #4


    Staff: Mentor

    The speed c is a universal constant. It is the only speed which is invariant, and it happens to also be the speed of light in vacuum as well as the speed of any other form of massless radiation. The speed of light in a medium is not equal to c.
  6. Aug 17, 2016 #5
    The speed of light is not slowing. You can test this easyly with an prisma at the end. You will see that the ones that come first are less uv/blue (heat) than the ones later. Because the medium absorbes and be heaten. Between put water or glass. The glass or water will absorbe the first ones. How longer the distance in the medium, how slower it will look. That's why you get the idea that light slows. My idea. Blaim it on me
  7. Aug 17, 2016 #6
    May i post here something about light? Because i got a general warning and i do'nt know what the post or not. But it is great knowledge to about light. I know a lot about the behavior of light to.

    I had told climate change and the absorbation of sunlight. Particles in our atmosohere absorbe sunlight. So in automn is the sun more red (less/blue) because that light/radiation has to travel a longer distance in our atmosphere. The moon is more red near the horzon for this reason,

    What i want to share is this and i think it's great, so does the light of an star. So dark matter and light etc;) if there were particles that absorbed light in our universum etc. I think that this is great to know.
  8. Aug 17, 2016 #7


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    Tahir, your responses are incoherent and wrong. The question was already answered in the first few responses.
  9. Nov 4, 2016 #8
    Question, is this true?

    (13.8 billion years ago all the mass of the Universe was concentrated in a small area. Since time slows as we near mass then the speed of light would have been hundreds if not thousands of times faster than the speed of light today. This would explain the inflation theory.)
  10. Nov 4, 2016 #9

    Vanadium 50

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    2017 Award

    No. It's abject nonsense.
  11. Nov 4, 2016 #10


    Staff: Mentor

    On that note, I think it is time to put this thread out of its misery.
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