What was the Big Bang?
The Big Bang is the most popular theory about the creation of the Universe. According to it, the whole Universe was created in a split second in one huge explosion. All matter was squeezed together into a tiny, super-hot, dense ball that was smaller than an atom. The ball gradually expanded as it cooled, then exploded, releasing energy and matter in all directions. We cannot see the Big Bang because it would have happened billions of years ago. But we can see that the Universe is growing steadily bigger. All the galaxies are speeding away from each other as the Universe expands.
What is the Universe made of?
The Universe is made up almost entirely of hydrogen and helium. These are the two lightest elements. All the rest of the matter in the Universe is very rare. Elements such as silicon, carbon and others are concentrated into clouds, stars and planets. The Universe is held together by four invisible forces. Gravity and electromagnetism are the two familiar forces. The other two kinds are strong and weak nuclear forces. These operate only inside the incredibly tiny nucleus of atoms, holding the tiny particles together.
How old is the Universe?
It is possible to calculate the approximate age of the Universe by looking at how fast distant galaxies are moving away from us. However, it is not possible for us to make this calculation accurately. Scientists have estimated that the Universe is between 13,000 and 18,000 million year old.