Hemma Vara, of Rangi Ruru Girl's School, asks :-

What is the shape of the universe and how big is the universe?

Alan Gilmore, an astronomer at the University of Canterbury's Mt John Observatory, responded.

This looks like a simple question, but it doesn't have a simple answer.

The most distant objects we see in the universe are probably more than 20 billion light years away from us now. They weren't that far away when the light we see started out from them, but the universe has expanded since then.

Skipping a lot of important detail, the present universe is probably around 100 billion light years across. (A light year is the distance light travels in one year: about 10 000 billion km, using U.S. billions.) Since the universe expanded from one point we have to assume it is a sphere.

The size of the universe depends on how fast it is expanding and how old it is. The current expansion rate is such that two galaxies 300 million light years apart will be moving away from each other at about 6000 km per second. Galaxies twice as far apart will be separating at twice that speed. The age of the universe seems to be around 14 billion years.

However, the rate of expansion might not stay constant. There is a theory that the early universe suddenly `inflated', expanded very quickly, then slowed to its present rate. That theory isn't proved, but it helps to explain certain properties of space. Recent observations indicate that the expansion rate is increasing again.

The study of the large-scale properties of the universe is called cosmology. It involves the complicated mathematics of relativity where our everyday notions of space and time don't apply.