Eli5: Why does light travel so fast?
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While there is no direct answer to your question of “why”, there is an interesting relationship between fundamental constants of the universe and the speed of light.
Light is an electromagnetic wave. That means that it is composed of electric and magnetic fields, whose oscillation directions are mutually perpendicular. There are two fundamental constants of the universe that govern, if you will, how easily magnetic and electric fields can oscillate in a vacuum. Those are the vacuum permittivity (ε0) and permeability (μ0). It turns out, not too surprisingly, that the speed of light can be equated from those two constants as
c=1/√(ε0μ0)
You could therefore say that light travels in a vacuum at the speed it must travel, given the fundamental structure of our universe.
μ0 and ε0 are actually defined in terms of c, not the other way around, but I have always found the relationship intriguing.
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