Universe is 13.7 billion years old

Simple version: Using Hubble’s Law, we can run the clock backwards, to see how long it has taken for it to have expanded to its current observable size
Ho = Hubble constant in km s-1 Mpc -1
1/Ho = Hubble time  14 billion years
But this all assumes that Hubble’s constant is really constant – is it?

Simple version: Using Hubble’s Law, we can run the clock backwards, to see how long it has taken for it to have expanded to its current observable size