Theories of the Universe

• Steady State Theory: The Universe has no beginning or end, it is expanding and new matter is being created as it expands.

• Big Bang Theory: The Universe started about 14 billion years ago in a huge explosion called the Big Bang. Since then the universe has been expanding and changing and may have an end depending on its density. Now new matter is being created.

What’s the evidence?

Doppler Effect• As an emergency vehicle’s siren

passes you, its pitch gets lower. This is known as the Doppler effect.

Doppler Effect• What two things does pitch

depend on?

• Pitch depends on the Wavelength and frequency of the sound wave.

Doppler Effect

Doppler Effect• The sound waves behind a moving

sound source become ‘stretched’, making the frequency lower and the wavelength longer and so the sound becomes lower in pitch.

• The opposite happens in front of a sound source.

• So what’s this got to do with the universe?

• This same effect happens with light, but sound doesn't make a noise, but it can change colour!

The picture above shows the EM spectrum. The wave length changes as you move along. Right in the middle we have visible light, which is what

stars produce. So what would happen to the light from a star if it was coming towards you?

Red Shift

The light we can see with our eyes is called visible light. The wavelength of visible light varies, the

violet part has a smaller wavelength (higher frequency) then the red part.

Red Shift

Stars produce mainly yellow light. If a star was to move away from us, the wavelength of the light

would increase. This would make the light appear red!

Red Shift

Stars produce mainly yellow light. If a star was to move towards us, the wavelength of the light

would decrease. This would make the light appear blue!

Red Shift

• This is the evidence for both theories, as they both state the universe is expanding. But what is the evidence for only the big bang?

The observation of red shift is a key piece of evidence for the Big Bang theory about the origin of the Universe.

The other key piece of evidence for the Big Bang theory is cosmic microwave background radiation (CMB).

This states that the Universe ‘began’ with a colossal explosion 13,700 million years ago and has been expanding ever since.

CMB is radiation remaining from the Big Bang explosion and fills the whole of the Universe.

This radiation has cooled as the Universe has expanded andis now slightly less than 3 degrees above absolute zero.

Cosmic Microwave Background Radiation