There are three proper distances worth keeping straight in one's mind: Today's (comoving) distance, the distance when the light set out, and the distance the light itself traveled.
Figure: Whittle's (upcoming) undergraduate textbook.
Three Distances in Cosmology |
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There are three proper distances worth keeping straight in one's mind: Today's (comoving) distance, the distance when the light set out, and the distance the light itself traveled.
Figure: Whittle's (upcoming) undergraduate textbook. |