Comments by "Mikko Rantalainen" (@MikkoRantalainen) on "What Actually Expands In An Expanding Universe?" video.

  1. To me James Clerk Maxwell is even more important than Einstein. As far as I know, Special Relativity and General Relativity directly follows from Maxwell's equations when you apply the single assumption that time is relative and speed of light is always contant. Obviously, that's a pretty bold assumption to do and you have to solve lots of complex math about the results which is where Einstein did most of the work. It could have been turned out that the universe doesn't work that way and the bold assumption is not true, but luckily for Einstein, his assumption was the correct one.
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  2.  Science Revolution  Walk away from the computer and breath. You might have your brain overheating slightly. Photon is not a particle in sense that you could stop it and measure its mass. However, some effects that photons cause to matter behave like it were a particle. And some other effects behave like it was a wave instead. This is called wave particle duality. For more information, see https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality As for the stars and galaxies billions of light years away - we don't know if they still exist or not. There's no known reason to believe that they wouldn't still exist but if something happened to them say 100 million years ago, we still wouldn't know about it because according to Einstein, there's no way any information can travel such distances faster than light.
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  3.  @TeguhNugrahaPratama  It's also interesting to note that Maxwell was able to correctly measure the speed of electromagnetic force fields caused by electricity and it was only much later figured out that light is actually electromagnetic radiation, too.
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