> I was immediately asking myself: what about the CMB? Surely that would have a stonking big anisotropy if the speed of light wasn't close to the same in all di

> I was immediately asking myself: what about the CMB? Surely that would have a stonking big anisotropy if the speed of light wasn't close to the same in all directions? No, you can always cancel it out by making the whole rest of physics suitably anisotropic too. Which would, of course, be ridiculous.