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The Big Bang
Scientists have gathered a lot of evidence and information about the universe. They have
used their observations to develop a theory called the Big Bang. The theory states that
originally all the matter in the universe was concentrated into a single incredibly tiny point.
This began to enlarge rapidly in a hot explosion, and it is still expanding today. This
explosion is called the Big Bang, and happened about 13.6 billion years ago
Evidence of the Big Bang
There are two key pieces of evidence for Big Bang theory. These are red shift and the
Cosmic Microwave Background radiation.
You may have noticed that when an ambulance or police car goes past, its siren is
highpitched as it comes towards you, then becomes lowpitched as it goes away. This
effect, where there is a change in frequency and wavelength, is called the Doppler effect. It
happens with any wave source that moves relative to an observer.
This happens with light too. Our sun contains helium. We know this because there are black
lines in the spectrum of the light from the sun, where helium has absorbed light. These lines
form the absorption spectrum for helium.
Spectrum of the sun
When we look at the spectrum of a distant star, the absorption spectrum is there, but the
pattern of lines has moved towards the red end of the spectrum, as you can see below.
Spectrum of a distant star
This is called red shift. It is a change in frequency of the position of the lines.
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.
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The light from other
galaxies is red-shifted. The other galaxies are moving away from us.
The further away the The most likely explanation is that the whole universe
galaxy, the more its is expanding. This supports the theory that the start
light is red-shifted. of the universe could have been from a single
Cosmic Microwave The relatively uniform background radiation is the
Background remains of energy created just after the Big Bang.…read more