Question: what is the big bang theory

Lyndsey Fox answered on 15 Jun 2011:

I believe it’s a sit-com shown on E4…

But if you want to talk astrophysics then the big bang theory suggests that a long time ago (about 14 billion years) the Universe started as a big explosion.
All the energy and matter which exists today came from this original explosion.

The evidence for this theory comes from two observations.

1. Light from stars in other galaxies is red-shifted.
It is called a red-shift because the colour red is at the longer wavelength end of the visible light spectrum. If light appeared to be at a shorter wavelength, it would be called a blue-shift.

Astronomers have found that the further from us a star is the more its light is red shifted. This tells us that distant galaxies are moving away from us, and that the further a galaxy is the faster it is moving away. Since we cannot assume that we have a special place in the universe this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else. The Big Bang theory says that this expansion started billions of years ago with an explosion.

2. There is cosmic microwave background radiation (CMBR) everywhere in space.

Scientists discovered that there are microwaves coming from every direction in space. Big Bang theory says this is energy created at the beginning of the universe, just after the Big Bang, and that has been travelling through space ever since.