Is minimum latency fixed by the speed of light? [closed]

Actually, it does not even travel close to the speed of light.

Firstly, the refractive index for glass is approximately 1.5, varying by the exact material. This means that light traveling through glass in a straight line only goes about 2e8 m/s, not 3e8.

And then you have to consider the curvature of the path. Even with single-mode fiber there is a lot of sideways drift along the entire run. This can easily increase the actual distance traveled by 15% or more. So what sounds like an incredible (although it actually isn't given such large distances) 3e8 m/s has been cut nearly in half.

Transmission with lasers and mirrors would be faster, but then you have to consider that things such as atmospheric perturbation, and even birds would cause communications trouble.