I think it's a pretty well-tested idea considering we experience it pretty much in our daily lives.
And actually, even though this is technically not correct since we're on earth which is a big ball with a gravitational field and we're neglecting acceleration, even if you're on a train moving at a constant velocity with windows and sound, you still wouldn't be able to prove that you were moving. All velocities are relative, that's the principle of relativity. This is getting a bit philosophical but how do you know it isn't the earth moving below the train that gives the appearance of motion (again ignoring that the earth is a big globe and other factors for sake of simplicity)? It's a question of your frame of reference. That's relativity.
As for the mathematics, what you're looking for is something called the Galilean Transformations, or something called the Lorentz Transformations which take into account the invariance of the speed of light. Those equations give you the ability to transform from one reference frame into another.
If you're looking for say, your position along the x axis in one reference frame compared to another in galilean relativity, while one reference frame is moving away from the other, the equation is $$x'= x-vt$$ Where t is time and v is the velocity.
In special relativity, where the speed of light is constant, this equation becomes $$x'= γ(x-vt)$$
Where $γ=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$ and c equals the speed of light. At low velocities, γ reduces to 1 and the whole equation reduces to the galilean transformation.
One chief difference between the lorentz transformations and the galilean transformations is that not only position changes between reference frames, but time does also, also known as time dilation.
As for why this principle of relativity is the case, i'm not really sure, it seems to be a fundamental symmetry of spacetime. There could be a quantum field theoretic explanation towards this but at this moment in time i am not aware of it.