Nice

Speed of light is constant

We got a little idea of why the speed of light if constant and that it really is based on the discussion on relative mass concept and experiments done, respectively but, How does it happen? Is really unanswered.

I merrily progressed to unit 23 and found myself floundering in confusion - I had lost the internalisation of the constant nature of the speed of light! So I'm back here again (and doing other reading) to get a better grip on the concept, not just an acceptance of the 'reality'. I figured that if one were to whack a rock or lead ball with a bat, it would shoot off at a measurable speed. If the ball were replaced with a golf ball, it would move faster. If the ball had zero mass and in a vacuum, just a light blow would cause it to shoot off really fast - if it were of truly zero mass then the speed should be infinitely fast!? So why is the zero rest mass photon restricted to the finite speed of light? Energy and Mass are related so perhaps the energy of the photon gives rise to pseudo-mass??

Binary stars give us a very strong evidence about the speed of light, awesome!