Pauline DeLong, age 13, of Carson City, Nev., for her question:
HOW BIG IS THE UNIVERSE?
The universe is made up of all the matter, light and other forms of radiation and energy that have been discovered by man. The universe also consists of everything that man believes to be present somewhere in space and time as a result of his theories. Most scientists do not know if the universe has a certain size.
Most astronomers think that bright, unusual galacies called quasars may be the most distant objects in the universe. Quasars may be as far away as 10 billion light years from earth.
Light from quasars takes so long to reach the earth that it must have been given off several billion years ago to be seen today.
Scientists cannot tell how far away a quasar is from studying its brightness alone. When an object that gives off light moves away from an observer, he sees the light as longer wave lengths. This apparent change in the wave lengths of light is called a red shift.
Scientists can study the red shift of a quasar to find out how far away the quasar is. The amount of red shift depends on the speed at which the object moves away from the observer. All the distant galaxies and quasars have enormous red shifts. Scientists believe this means that the universe is expanding, with every part of the universe moving away from every other part. This is the fundamental feature of the universe that scientists try to explain with various theories about the size of the universe.
The universe includes the earth and also everything in the solar system. All of the stars, of which the sun is one, are part of the universe. More than 100 billion stars are grouped in the shape of a giant circular galaxy called the Milky Way. The Milky Way is about 100,00 light years across. A light year is the distance that light travels in a year: about 5.88 trillion miles.
Scientists say there are at least as many galaxies in the universe as there are a stars in the Milky Way.
Galaxies tend to be grouped together into clusters and clusters are grouped into superclusters. Most astronomers believe that superclusters are the largest groups that can be distinguished in the universe.
Cosmology is the study of the behavior of the universe.
Most cosmological theories about the universe are based on the idea that any part of the universe is like any other part having the same age.
Albert Einstein's general theory of relativity also forms part of the basis for theories about the behavior of the universe. This theory, in turn, is based on two beliefs: that no signal can travel faster than the speed of light and that the laws of physics are the same everywhere in the universe.
Theories resulting from these ideas involve a universe that expands and contracts.