Comments by "bj0rn" (@TheLivirus) on "Cosmology | Lecture 3" video.

  1. To me it sounds weird that the energy of a photon would decrease over time since it gets stretched. I mean the number of wavelengths and their corresponding amplitudes are preserved right? If a photon's energy was proportional to the wavelength wouldn't it gain energy upon entering a medium with higher refractive index, thus violate the conservation of energy law? But then again, I'm altogeather uncomfortable with quantum mechanics.
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  2. Is the velocities of the outer matter in a galaxy relativistic? If so, wouldn't this play an important role when determining the mass of a galaxy?
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  3. @telephas1c Yeah that makes sense I guess.
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