The Universe - CCEA

• The origin of the Universe (the Big Bang).

• Evidence for the Big Bang.

Scientists have gathered a lot of evidence and information about the Universe.

They have used their observations to develop a model called the Big Bang to help explain its formation and evolution.

The theory states that about 13.8 billion years ago all the matter in the Universe was concentrated into a single incredibly tiny point.

From this tiny point, the whole Universe expanded outwards to what exists today.

• The Universe is thought to have originated 13.8 billion years ago from a very small, extremely hot and dense region called a singularity. The Big Bang was a massive expansion that blew space up like a gigantic balloon.

• Initially, the Universe expanded rapidly. Rapid expansion is always accompanied by cooling, so, as the Universe got bigger, it cooled down. This enabled protons and neutrons to form.

• Further expansion and cooling allowed protons and neutrons to combine to form nuclei.

• The Universe continued to expand, although now more slowly. As it cooled even more, electrons combined with neutrons and protons to form atoms of hydrogen.

• The force of gravity acted on the atoms of hydrogen, pulling them together into bigger and bigger clumps.

• Some 400,000 years later the first stars formed from the clumps of hydrogen and begin to light-up the Universe.

Evidence for the Big Bang includes:

• All other galaxies are moving away from us.

• The further away a galaxy is, the faster it is moving away.

• The Universe is filled with the left over energy from the Big Bang known as Cosmic Microwave Background Radiation, CMBR. This is received from all parts of the Universe and is thought to be the heat left over from the original explosion.

You may have noticed that when an ambulance, fire engine or police car goes past, its siren is high-pitched as it comes towards you, and then becomes low-pitched 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 towards or away from an observer.

If the object is moving towards an observer, the waves are shifted to a higher frequency, shorter wavelength.

If the object is moving away from an observer, the waves are shifted to a lower frequency, longer wavelength.

This happens with light as well as sound.

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.

When we look at the spectrum of a star in another distant galaxy, the absorption spectrum is there, but the pattern of lines has moved, or ‘shifted’, towards the lower frequency, longer wavelength, red end of the spectrum, as you can see below:

This is called red-shift.

Light is shifted towards the long wavelength, red end of the spectrum.

This tells us that:

• Other distant galaxies are moving away from our galaxy.

• The Universe is expanding.

Astronomers have found that the further from us a star is, the more its light is red-shifted.

This tells us that:

• The further away a galaxy is, the faster it is moving away

Since we cannot assume that we have a special place in the Universe, it suggests that everything is moving away from everything else as you would expect with an explosion.

Further evidence for the Big Bang comes from the discovery of cosmic microwave background radiation (CMBR).

Astronomers discovered cosmic microwave background radiation in the 1960s.

The wavelength of this radiation appears to be the same no matter where in space that it comes from and it corresponds to a temperature of about –270 °C.

It comes from all directions and from all parts of space.

Scientists believe that the continuous microwave background radiation is the remains of the heat energy from the Big Bang, spread thinly across the whole Universe.

The Big Bang is currently the only model that explains the existence of CMBR.