P1.6 The Origin of the Universe

The Universe seems to be expanding

• All the galaxies in the Universe seem to be moving away from each other
• According to the Big Bang theory, all the matter and energy in the Universe must have been packed into a very small space
• It then exploded from that single point and started expanding

Evidence for the Big Bang theory - Light from other galaxies is RED SHIFTED

• When we look at light from distant galaxies we see it at longer wavelengths than it is
• The light is shifted towards the red end of the electromagnetic spectrum. This is RED SHIFT
• It is the same effect as the vroooomm from a racing car - the engine sounds lower pitched when the car is gone past and is moving away from you. This is the DOPPLER EFFECT

The Doppler effect

• When something that emits waves (sound or light) moves towards you or away from you, the wavelengths and frequencies seem different compared to when the source of the waves is stationary
• The frequency of a source moving towards you will seem higher and its wavelength will seem shorter
• The Doppler effect happens to both longitudinal waves (sound) and transverse waves (light and microwaves)

Evidence for the Big Bang theory - Light from other galaxies is RED SHIFTED

The further away a galaxy is, the greater the red shift

• Measurements of the red shift suggest that all the galaxies, apart from a few close ones, are moving away from us very quickly in every direction

• More distant galaxies have greater red shifts than nearer ones

• This also means that more distant galaxies are moving away from us faster than nearer ones

• This is evidence that the whole Universe is expanding

Evidence for the Big Bang theory - There is MICROWAVE RADIATION coming from all directions

• Scientists have detected low frequency electromagnetic radiation coming in from all parts of the Universe
• It is called Cosmic Background Microwave Radiation (CBMR) and comes from the Big Bang