In a recent popular video by Veritasium it is claimed that no one has devised an experiment that measures the one-way speed of light, and that in theory a directional difference in the speed of light is possible.
I can understand that it's difficult to design experiments to test this on earth, but does cosmology not provide us with pretty strong bounds on the devation of the one-way speed of light versus the two-way speed of light?
I would imagine that if light traveling in one direction is significantly slower than the other way around we would see cosmological effects that we do not:
A significant gradient in the temperature of the cosmic microwave background radiation. In the extreme event that in one direction the one-way speed of light is instant, we would not see a CMBR in one direction at all.
A significant difference in the development stage of galaxies in one direction v.s. the other. E.g. more young stars that pulsate less than older stars.
Is my intuition correct? Or would the night's sky in a universe with a one-way speed of light that significantly differs from our conventional two-way speed of light look identical to one that matches it?
