Expert: Jayendra Upadhye - 6/13/2008

Question
Hello Jayen,

Many thanks for below answer. But I'm still wondering about this: for example if the Hubble constant (HC) is 70 km/s per MPC, then the observable universe would be about 13.971 billion light years away in all directions, because beyond that distance, recessional velocities will be > C, if HC is 75 km/s per MPC, then the distance will be 13.04 billion light years, if 80 km/s per MPC, then the distance will be 12.225 billion light years .
Are these numbers then automatically regarded as THE AGE OF THE UNIVERSE?? Could it be possible a 13.971-billion-years-old universe has a HC of 80 km/s per MPC, thus in this universe, at a distance of 12.225 billion light years, recessional velocities = C ??

Thanks again

Indro
Jakarta, Indonesia

YOUR PREVIOUS ANSWER:

Hi Indro,
There is more to this than "meets the eye"!
1) -
You see the early history of the universe is "inflationary".
Meaning the universe doubled and quadrupled in size, and the bang happened not at a single point but "over an area" so to speak.
That implies it expanded faster than light during that phase, "appearing" at more than one location "almost simultaneously" in time.
And thus violating the sacrosanct speed/velocity limit C.
From a "wee bit" later in time, it proceeded to expand at velocity C.

Obviously, two points at either opposing ends of this universe would never see one another!!

We will forever be cutoff from those areas, by virtue of their location in space and time during the inflationary phase.

2) - for a time after the bang, matter / energy or whatever one calls that state, was too hot to exist as separate distinct entities, and so no information is available in the CMB (Cosmic Background Radiation) about it.

The decoupling happened after a considerable time elapsed. That ‘flash’ when electromagnetic radiation decoupled as a separate entity, is the source of the CMB, and also its isotropy. (And small scale anisotropy, which predicted the large scale structure of the universe, as amplified by gravity).

3) -
Then the universe entered the dark-age, when the first stars were in the process of forming, and the skeletal spiral galaxies (globular clusters were already forming in the galactic haloes) emerged. In due course these would collide and form irregular and elliptical galaxies.

The universe was expanding during that dark time and by the time the first stars winked on in the visible light, (which we would some day observe for red shifting), further volume of the universe "went over the visible edge"!

So fitting that 13.7 billion years into all this is a bit tricky.
All I can say is that from that "first winking" of the stars, the time elapsed is 13.7 billion years.

I do not make it a point to remember particulars, after all one can always "look them up". But the foregoing is what happened.

You may trace the recession rate with distance from sites evaluating the Hubble's constant, and distance relationships with recession rate, plug in the value and get your answer.

Elsewhere on the site I have listed those sites in other answers.
But I think I should leave some "research" to you so you can share the excitement.

Regards
Please do rate the answer if you find it informative.
Jayen  

Answer
Hi,
I cannot throw much light beyond what i said earlier.

There are some disputes regarding valuation of the hubble's constant itself if memory serves me right.
But i havent readup on that much recently.

secondly as we see farther out, we see farther back in time.
At the "edge", if you see all stars in general that belonged to the universe say 12 billion years ago. then knowing the time that would have elapsed from the time of the matter energy decoupling or time of release of the CMB (Cosmic Background Radiation), to the observed state of the universe at the edge, one could reach the time when the bang started and thus predict the age of the universe.
(within the framework of theory predicting what happened immediately after the bang, till the CMB flash).

The current temperature of the background and observed volume of the universe, can also help us do a back calculation knowing that by nature of its definition, the universe resembles gas that is cooling adiabatically.

I cannot offer much more than this on the subject.

Regards
Please do rate the answer if you find it informative.
Jayen