If we assume the distance between two points is given by ________. d = R Δx, we can assume that λ_0 = R_0 Δx. And when we receive the emission it will be: λ = R Δx. So using the idea of redshift, we can deduce... fracλλ_0 = fracRR_0. Now, here's where I'm confused. Assuming we detect the wavelength now from an emitted wavelength (some time ago). We are only getting a ratio between the scale factor then and now, in theory, wouldn't the wavelength be stretched by R_0 as well (at whatever time that is) when it was first emitted. So if we decide to use the spectral lines that we find on Earth, since they are the actual values, wouldn't it not match if we compared it to the wavelength initially emitted since it would have been stretched. Another question is, Can we also measure the distance now? (without finding the distance at the time of emission, finding the speed (assume constant) till it reaches us and multiplying it by the time that has elapsed since then, and add the two and giving the distance now)