Evolution of the Universe

Gravitation is one of the four principal forces in the Universe. It is the mutual attraction between masses. If you placed two peas one metre from each other in empty space where they were not influenced by other forces, they would move toward each other until they touched, like peas in a pod.

The same thing happens to atoms. When the enormous quantities of hydrogen and helium raced through space after the Big Bang, their atoms began to collect in giant gas clouds. They pressed together, released energy and formed the first stars.

When a massive star has no more hydrogen to burn, it can explode in a supernova. Pressure and temperature then rise, and under these conditions, helium and hydrogen atoms are fused into more complex atoms such as iron, oxygen and carbon. This is the way that most of the elements were formed. All the objects of our world are built up of atoms created in stars billions of years ago.

A supernova explosion tosses material out into space, in a small version of the Big Bang. Gravitation causes these materials to form new gas clouds that in turn form new stars. This is the way our solar system, and the Earth where we live, were made.

Stars and planets have their allotted lifetimes. When they die, they give rise to new planets and solar systems. In much the same way that plants are food for animals, which in turn fertilize the earth and make plants grow, you might say that the Universe develops in a pulsating, cosmic circle of life and death.