> That would require the emission and absorption events location in the space to be the same would it not? I think they're referring to the distance in Minkows

> That would require the emission and absorption events location in the space to be the same would it not? I think they're referring to the distance in Minkowski space,[0] where the time component and space component cancel out for light. [0]: https://en.m.wikipedia.org/wiki/Spacetime#Spacetime_interval https://en.m.wikipedia.org/wiki/Spacetime#Spacetime_interval