# How to calculate the age of the universe with redshift

1. Apr 3, 2007

### b_o3

Hi i am confused as to how to calculate the age of the universe with redshift
say for example

The age of the universe now is 13.4 billion years old (and a critical universe).
How do i find the age of the universe if it was a redshift at say 0.6??

Do i have to find the scale factor first?

2. Apr 3, 2007

### b_o3

someone help me with it plz

3. Apr 4, 2007

### malawi_glenn

The scale factor is related to the red shift.

R(t) = 1/(1+z) ; where R(t) is the scale factor at time t. R(t_0) = 1, t-0 is today.

What we want is the "lookback time" (t_L)

For a flat Universe, this is:

t_L = t_H * (2/3) * (1 - (1+z)^(-3/2))

t_H is the Hubble time ( 1 /H_0 ); approx 13.8 Gyr.
H_0 is the Hubble constant.

t_L = 0.337 t_H

I dont know what values you have in your book and so on, but this one way to solve it, there is probably more. The way to deduce the forumulas is pretty straightforward, it should be stated in our course book in cosmolgy.