# The One-Way Speed of Light - Again!

A little while ago I provided input to a video by Veritasium on the One-Way Speed of Light. You can watch the video __here__ . This is not a new idea - Einstein realised that you cannot measure the one-way speed of light, only the two-way speed, and so we assume that the one-way speed is equal to the two-way speed.

I am amazed by the reaction of most physicists when they encounter this. They are certain it must be wrong because, well, because... and a lot of foot stamping ensues. Once you realise this is a coordinate transformation, and so all the transformations are preserved, so the observables come out to be the same, eventually resignation sinks in.

But I still get emails etc with new and interesting methods to measure the one-way speed. Here's the latest.

So, I went through the equations, and (as expected) the result of the experiment is the same irrespective of whether light is isotropic or anisotropic. Physics wins again!