- #26

bapowell

Science Advisor

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Sure, that works. I only mentioned the explicit mapping so that you can see how to go from k <-> N in general. But, yes, if you have k = aH as a function of N, you just pick the k of interest, read off the N, then solve for r at that N.Oh, that is why I should specify at which ##k=aH## I want to measure ##r## and that would give me the corresponding ##N##. Typical back in the days are ##aH=0.05/0.002 h^{-1} Mpc##. But why should I take the derivative of ##k=aH## with respect to ##N##? I could just plot ##k=aH## vs ##N## and find the ##k=aH## based on Planck data and get the corresponding ##N##?

That's right.As a sidenote, is ##k## defined as ##k=aH##? I thought ##k## is an independent quantity and we just set a condition ##k=aH## to specify the Hubble crossing.