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The dreaded derivation, Re: your starship-design email of 8/20
Steve VanDevender writes:
> We have an observer P whose spacetime location is [ t x y z ]. We want
> to find possible paths that correspond to light rays passing from S(t')
> to P, or from P to S(t'). We can characterize this relationship with
> the equation:
>
> (P - S(t'))^2 = 0
Sigh. While editing that last letter, I omitted the explanation that I
use shorthand U^2 = U dot U for vector quantities; I use that convention
frequently in my notebooks, but it would probably help you to know that
explicitly when reading the above-quoted section.