Why the speed of light is constant?

Einstein considered the theoretical aspects. It can be derived from Maxwell's equations that the speed at which electromagnetic waves travel is: 

c = (ϵ0μ0)^(−1/2) = 1/√ϵ0μ0.

Since light is an electromagnetic wave, that means that the speed of light is equal to the speed of the electromagnetic waves. 

ϵ0 and μ0 are properties of the vacuum and are constants, so c will also be a constant.

According to Maxwell equations, an electromagnetic wave moving with velocity 

v = 1/√ϵ0μ0. 

Since light is an electromagnetic wave, that means that light is also propagating at this speed in vacuum. 

And since both ϵ0 and μ0 are constant, that means 1/√ϵ0μ0 is also a constant. Hence light moves at a constant speed in vacuum. 

#Maxwell 

Expansion of space is rather expansion of distance.

Space is an infinite three-dimensional extent, where objects and events contain relative position and direction. Dimension is an extension of the abstract concept of mathematics. For example, a line is one-dimensional, a plane is two-dimensional and space is three-dimensional. Therefore, space is not an entity but an abstract concept.

Expansion of space is rather expansion of distance among distant gravitationally bound objects within dimensions of space:

More specifically, spatial expansion is the increment in the distance between two distant points in the dimensions of space, at least in intergalactic scale. This is increment in distance in metric scale, where space itself does not expand. Space is rather the metric scale. 

Dark energy appears to act like antigravity, so antigravitational field interacts with gravity of gravitationally bound objects within dimensions of space, where antigravity is stronger than gravity, and so the galaxies recede from one another, and that increases distance between two distant points within the dimensions of space.

Reference Explanation

#Intergalactscale #distanceincrement #expansion #antigravity #antigravitationalfield