Ask Ethan: Why must time be a dimension?
Ethan Siegel

This was so good I had to read it twice. I wonder if you could do something similar for red-shift. I know I’ve read an explanation before but, since all photons are moving at the same speed how do they differ?

And if we are looking at a galaxy that is 13 billion light years away has the photon traveled more or less than 13 billion light years since the universe has been expanding that whole time? And, getting back to time again, I suppose from the point of view of the photon no time has passed at all?

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