The assumption of bounded/unbounded space

[michel123456]

So part of the formula had this factor a(t) multiplying it.

 

Silly question: what is its value?

 

..............

Wait a moment. Are you saying that this a(t) factor can be interpretated as acting upon time? Instead acting upon space?

[ajb]

[math]a(t)[/math] is a function of time, it describes the relative expansion of the universe. How it evolves is a dynamic question in GR and can be solved depending on the matter content.

 

In a matter dominated universe we have [math]a(t)\approx t^{2/3}[/math] and for a radiation dominated universe we have [math]a(t) \approx t^{1/2}[/math] (we have assumed a perfect fluid equation of state)

 

For details pick up any book on cosmology, I recommend Andrew Liddle's "Introduction to Modern Cosmology".