Expert: Philip Stahl - 9/12/2008

Question
hello Philip,

It would seem that lately everybody is saying that the universe is 13.7 billion years old, but i also watched an Imax show that said we have stars older than this date-- up to 20 billion years old and that dating the stars is more accurate. What is going on here? And also I would like to ask how far can our best telescope see?

with best regards

Riccos

ps thanks very much for answers on dark matter!

Answer
Hello,

First off, "everybody" is not asserting a specific age for the universe. The 13.7 billion figure is one example, based on one accepted value for the Hubble constant but that is all. There is a certain segment that has other values in mind.

Second, the age figure is not some exact number engraved in stone, or whatever. It isn't even a measurement, but more in the way of a best estimate based on a collection of data and may be off by +/- 1 billion years, maybe even more.

Many think the figure ought to be considered a LOWER bound on the age, not an upper one.

Re: ages obtained independently, radioactive isotope studies yield up to sixteen billion years for our Galaxy, and the ages of the oldest star clusters put the limit at about 14 billion years.

If the 14 billion (approx.) Hubble-constant based age is agreed as a lower limit, this is no problem nor is there any contradiction.

At the same time, the "20 billion year" age cite your Imax noted needs to be taken with a grain of salt. First, because I have seen no (prfoessional journal)citations anywhere for stellar ages on that scale, and second, because it is an Imax film after all, and they may have simply been exaggerating for effect.

I would be much more impressed if you found a library text or other book that gave such a figure, and actually *named the stars* of such advanced age- as opposed to an Imax effort tossing out generalities.

As for as how far the best telescopes can "see" this would correspond to the most distant objects that can be pinned to a specific age. Right now that is around 12-13 billion light years for certain quasars, and 13 billion light years for one galaxy.

See, e.g.

http://news.nationalgeographic.com/news/2008/02/080213-AP-galaxy-pin.html

Hope this sheds some light!