Expert: Jayendra Upadhye - 10/14/2008

Question
Hello Jayen,

I have one question:
Does Hubble's Constant imply the age of the Universe?
Example: If Hubble' Constant = 70 km/s/mpc,
        then at 300000/70*3.26 = 13971 --> is this the age
        of the universe in million years??

Thanks

Indro Cahyono
Jakarta, Indonesia


Answer
Hi,
Refer:- http://en.wikipedia.org/wiki/Hubble's_law

You have used the 3.26 as the parsec to light year conversion.

you have used the equations:-
v*t=distance travelled.

v=300,000 km/sec as light years involves travelling at speed of light.

Now 70 km/sec/mpc = (70 km/sec)/(3.26 Mly) has units of inverse time.
So we can use hubble time as (3.26 Mly)/(70 km/sec).

Hence v * t = distance travelled corresponds to
(300000 km/sec)*(3.26 Mly)/(70 km/sec)= (300000*3.26)/70 = 13971 Mly.

That is right.

refer to the above link:-
[Hubble time:-
The Hubble constant H0 has units of inverse time. We can therefore define “Hubble time” as 1/H0.
The value of Hubble time in the standard cosmological model is 4.35×10^17 sec or 13.8 billion years (Liddle 2003, p. 57).
The phrase "expansion timescale" means "Hubble time".

Hubble length:-
The Hubble length is a unit of distance in cosmology, defined as c/H0 or the speed of light multiplied by the Hubble time.
It is equivalent to 4228 million parsecs or 13.8 billion light years.
(The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.)
].

So basically you have calculated hubble length!

Yes, the hubble's constant does imply the age of the universe.

However the constant itself is dependent on epochs, or time since the bang.

regards
Jayen