Scale factor Definition and 56 Threads

Hi, I am in my second astronomy course and just received a twenty question take home final exam, and I am having trouble with two of the questions. In 2004 astronomers reported finding evidence that certain white dwarfs are 12.1 +- 0.9 billion years old. Assuming an inflationary model in...

EDIT: I corrected a typo below: I had forgotten to put my entire expression for a(t) to the power 1/3. It's corrected now This may sound like a silly question but it's bugging me quite a bit. Consider a cosmological model, let's say the simple case of no pressure, no cosmological...

I will be writing my final exam tomorrow evening, and I am currently terribly stuck on the following practice problems. I have posted my thoughts below each problem. They look tricky to me. It would be very nice if someone could help me out and I will remain eternally grateful for your help...

We are given a form of Einstein's field equations: 3R'' = -pR R''R + 2((R')^2) = p(R^2) where p is a constant and R' = dR/dt Assuimg that R and R' are both positive, we are asked to show that the general solution is R(t) = A*[(t-ti)^(2/3)] I'm very confused about this. If we...

What is the ratio of the scale factor now to the scale factor at the end of the inflationary era? Edit: In other words, what is the z value of the end of the inflationary era?

The scale factor in the R-W metric is there to account for the expansion of the universe. My question is whether this scale factor is put in by hand just to account for observations? Or can it be derived from more basic assumptions? Thanks.