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Speed of light/electromagnetic waves is constant??

  1. Jan 20, 2016 #1
    Since Edwin Hubble proposed distant galaxies move apart from each other as spectra of each galaxy is shifted towards the red end. this created the law that universe is expanding exponentially since big bang. and these galaxies spectra are due to stretching of wavelength of light incident from moving apart galaxies. Stretching more wavelengths of light could been light disappears completely? Although, photons acquire their energy and speed in universe. till its wavelength have affected so does it speed too?
     
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  3. Jan 20, 2016 #2

    BvU

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    Hello Yash, :welcome:

    No, it doesn't disappear. But the wavelength gets longer and longer the further you look. Until you see the 'light' from the big bang -- when the wavelength is in the microwave range. The so called cosmic microwave background. Very interesting subject.

    Speed stays the same: 299792458 m / s exactly.
     
  4. Jan 20, 2016 #3

    Chalnoth

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    It will eventually, though! After about a trillion years, redshifts will be to the point that no galaxies outside the local cluster will be visible as the wavelengths of their light will have redshifted to be longer than the cosmological horizon.

    Of course, the Earth will be long gone by then.

    Not really. The expansion has changed over time as the density of the universe has changed. Only in the special case where the density is constant is there exponential expansion (which may be the case in the far future, if the cosmological constant is non-zero).
     
  5. Jan 20, 2016 #4

    Drakkith

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    It does not. A photon of any energy travels at c in a vacuum.
     
  6. Jan 20, 2016 #5
    Outer space isn't vacuum! so? Although classical law stated that speed of light is constant in vacuum, going to lesser in denser medium and zero in superatomic field. Condition of ideal vacuum is not satisfied by expanding space between galaxies!!
     
  7. Jan 21, 2016 #6

    Drakkith

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    Of course it is.
     
  8. Jan 21, 2016 #7

    Chalnoth

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    It's close enough that it doesn't really matter.
     
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