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I was thinking about the Hubble's law and I know that it's determined as [tex]H(t)=\frac{1}{a(t)}\frac{da(t)}{dt}[/tex] and then, thinking in the derivate of the scale factor as the speed, we've de usual formula [tex]v(t)=H(t)D[/tex]

But my question is: the distance is the distance we observe the object (so now it's in farther because of the time that takes the light to go across these distance) or the real distance of the object?

In other worlds: is the distance of the galaxy when the light was emmited or the real distance at the moment of observation (despite we observe it nearest)?

I was thinking on it and trying to solve it using the derivation of the formula but I'm not convinced on any option.

Thanks,

Javier Chornet.

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# A What distance is used in Hubble's Law.

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