- #1
mistergrinch
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OK I'm still new to cosmology and this question is bugging me: if a photon is emitted toward me from a distant galaxy at a distance D, how do I calculate the time it takes to reach me? I assume the universe is expanding exponentially with a DeSitter scale factor a = exp(Ht), (H = Hubble constant). Is there a simple way to do this calculation?
I tried using special relativity velocity addition to add -c + Hx, where Hx = speed of expanding space at a distance x. This gives me dx/dt = (-c + H*x) / (1 - H*x/c) = -c. I.e. t = D/c. Is this correct? Intuitively it seems like the expansion of space would increase the time it takes for the photon to reach me.
I tried using special relativity velocity addition to add -c + Hx, where Hx = speed of expanding space at a distance x. This gives me dx/dt = (-c + H*x) / (1 - H*x/c) = -c. I.e. t = D/c. Is this correct? Intuitively it seems like the expansion of space would increase the time it takes for the photon to reach me.