- Astronomers have observed that other galaxies are moving away from ours at great speed.
- Based on these observations, astronomers concluded that the universe is expanding.
- They then developed a theory about how the world began. This theory is called the Big Bang Theory.
- Before the Big Bang, the entire universe was compressed into a tiny, hot, dense mass. Then there was a huge expansion or inflation that allowed all of the universe's matter and energy, as well as space and time, to form.
- The Big Bang generated space with matter spread throughout it. Then the force of gravity began to bring matter together to form stars and galaxies and all the other types of space objects.
- The Big Bang Theory leaves some major questions unanswered, for example what caused the Big Bang?
The detection of cosmic microwave background{CMB} radiation is seen as important evidence for the Big Bang. The radiation is received from all parts of the universe and was detected by scientists using radio telescopes and satellites. Those who support the Big Bang theory say that this is energy created just after the Big Bang.