Sorry, you're right. There was a deeper reason I was asking however. There seem to be two different ways in which the scale factor can be normalised, at least as far as I can see. Either you can:
1) Change your units of time such that t_0 = 1 , and use a(t) = t^{2/3}
2) Normalise the...
Hello all! I'm trying to understand the standard normalisation of the scale factor to be set to 1 at today's time. Looking at the first Friedmann Equation for a spatially flat Robertson Walker metric with no cosmological constant gives
\frac{\dot{a}^2}{a^2} = \frac{8\pi G}{3}\rho
If we...