Scientists believe that about 14 billion years ago all matter in the Universe was in one extremely tiny and dense place. It then suddenly exploded, and has been expanding ever since. This expansion is shown by the red-shift of galaxies and the energy of the explosion can be seen everywhere in the Universe as the CMBR.
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If we examine the light spectra for distant galaxies we can see that the wavelengths of the light have become longer. We call this stretching of the waves ‘red-shift’. It tells us that the galaxies producing the light are moving away from us .The further away a galaxy is, the greater its red-shift, so it is moving even faster. This is evidence that the Universe is expanding and so it supports the Big Bang Theory.
Microwave radiation can be detected EVERYWHERE in the Universe. These are the stretched remains of high energy gamma radiation that would have been produced in the explosion that created the Universe. They have stretched because the Universe is expanding. |
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This is called the Doppler Effect. If something that emits a wave moves whilst it is doing so (imagine a noisy motorbike coming towards you then going further away, emitting sound waves the whole time) then the wavelength of the sound will become shorter as it is moving towards you, increasing the frequency, and stretched as it is moving away, decreasing the frequency.
You will hear this as a change in pitch, getting higher as it approaches and lower as it moves away. The same thing happens for a moving object that is emitting light waves –e.g. a galaxy. |
The further away a galaxy is the greater its red-shift and hence the faster it is moving away from us.
More distant galaxies have greater red-shift and therefore are receding faster because the space between all galaxies is stretching as the universe expands.
