# Age of the universe

Please can somebody explain how the age of the universe can be determined using Hubbles Constant?
If the constant is taken as 10km/s (just for the sake of easiness), how can this be figured out using calculations?

I appreciate any help!

Ambitwistor
It depends on which model of the universe you're using. e.g., if you take a simple matter-dominated Friedmann cosmology with zero cosmological constant, you end up with the age of the universe equalling two-thirds of the reciprocal of the Hubble constant. You work out formulas from this from the Friedmann equations for the evolution of such a universe (which are in turn derived from the Einstein field equation of general relativity). See, for example:

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age of universe

Thankyou for your help but what you gave me is a bit over my head.
"I have been given the task the Hubble constant is thought to be in the range 10 - 20 km/sec ^-1.
What age range does this imply for the universe?"
I am not sure where to begin...

Ambitwistor

Convert the value for the Hubble constant from km/sec/Mpc to 1/sec, and take the reciprocal. That will be roughly close to the age of the universe (in seconds); you can multiply by 2/3 if you want a Friedmann matter-dominated universe with zero cosmological constant, or multiply by some other factor if you want a different model.