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RobertLee2354 t1_j8xu7iy wrote

Reply to comment by Mammoth-Mud-9609 in ELI5: Why is light extremely slow in terms of the size of the universe? by AskSouth

What was the point of this response lol? The Universe is big and light does move pretty slow in comparison to the scope of it. The correct answer is nobody really knows why the speed of light is the speed of light, and not faster or slower.

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left_lane_camper t1_j8y0hpo wrote

The speed of light is directly related to the permittivity (ε_0) and permeability (μ_0) of free space, via

c = ( ε_0 μ_0 )^1/2

as a consequence of building the wave equation from Maxwell's equations. Though whether this answer is in any way satisfying depends on whether one considers the speed of light or these other EM properties of free space to be more fundamental (and, in general, we usually define ε_0 and μ_0 with c as well, simply by re-arranging the equation above). But changing c would require changing one or both of these other fundamental constants as well.

My personal favorite answer, though, is when you ask someone who does GR or cosmology research about why the speed of light is what it is and they look at you like you have three heads and say "I don't know what you mean, the speed of light is exactly dimensionless 1".

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RobertLee2354 t1_j8z3gbt wrote

yup. that's why gravitational waves also move at the speed of light. thats the fastest anything can move through the fabric of space-time.

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