GCSE SCIENCE PHYSICS HIGH SCHOOL - The Universe - Big Bang - What causes the Doppler Effect? - Why does Red-Shift mean that the Universe is Expanding?

gcsescience.com 42 gcsescience.com

The Universe - Big Bang - Red-Shift - Expanding Universe.

Following on from the previous page, imagine that the
same object is now moving away from you at the same speed.

During the time it has taken to emit one complete wave,
the object will have moved 0·1 metres away from you.
The wavelength has increased and the frequency decreased
because the whole wave is now 1·1 + 0·1 = 1·1 metres.

An increase in the wavelength of light is called a red- shift.
In reality light travels very fast and you can't tell that
the wavelength has changed unless the object emitting
the light is moving extremely fast. The amount of time
it takes to emit one light wave is so very small. No object
seen on Earth could have moved far enough in this
short time to produce a noticeable change in wavelength.

In summary, light from an object that is
1. Moving fast towards you - wavelength decreases - blue-shift.
2. Stationary - wavelength stays the same - no shift.
3. Moving fast away from you - wavelength increases - red-shift.

Since the light from other galaxies is red-shifted, these
other galaxies must be moving away from us very quickly.
The further away the galaxy is, the greater the red-shift
and the greater the speed at which it is moving away from us.

If the galaxies in the Universe are moving away from us in
all directions, then the Universe itself must be getting bigger.
This has led to the belief that the Universe is expanding.

Links Universe The Solar System Revision Questions

gcsescience.com Physics Quiz Index The Universe Quiz gcsescience.com

Home GCSE Chemistry GCSE Physics