Hey RobSab

Here's a great new site

http://www.newscientistspace.com

Enjoy
Dave

Hello, Socks.

Astronomers are very careless when discussing the size of the universe. Usually it does not matter, but now that they are beginning to reach cosmological distances, you can expect more and more problems like this.

First, current theory is that the universe is a lot bigger than the observable universe, which is currently a sphere centered on the Earth [See startling information at the end of this post]. The observable part keeps growing at the speed of light, so more of the universe keeps coming into view.

Second, space continues to expand, though at a slow rate, so that if you mark two spots in space a million light years apart, then measure them again a few million years later you will find that they are more than a million light years apart. General Relativity says that this expansion is slowed by gravity, so a dense young universe would decelerate quickly. If you had marked two spots in space a light year apart a million years after the creation, they would be more than a thousand light years apart today. [At least, that is what I seem to recall.] Space is expanding much more slowly today. So the rate of expansion is not a constant, but a function of time. In 1998 we finally got some observations supporting an old hypothesis that the rate of expansion would eventually start speeding up again, so we now think that it reached a minimum before Sol and Earth formed and has been slowly speeding up for billions of years.

When the gamma ray burst occurred 12.7 billion years ago, it was noticeably closer to the Earth than 12.7 billion light years. But the gamma rays had to cover space that kept being created in front of them until they finally reached Earth. And space was also being created behind them. So the gamma ray burster is a lot farther away than 12.7 billion light years today. If I remember correctly (and I probably do not) the radius of the observable universe today is not about 13.6 billion light years but more like 45 billion light years. Don't put too much faith in my fallible memory. It might be 75 billion light years.

But the point is, accurate figures for this expansion are only beginning to fall into place, so astronomers are used to making statements that ignore the expansion of the universe. . . . except when they do include it, confusing everybody.

mycrofth

Thanks Dave. I think I may get to like this site. I usually spend a lot of time on the NASA web site which is the most amaizing resource library I have ever come across..... it is however a highly complicated site to nagivate, but most fullfiling when you are looking for something specific.