GCSE Physics P1 Question

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The 'Big Bang' Theory uses red-shift as evidence to explain the beginning of the Universe.

How does red-shift from distant galaxies provide evidence for the beginning of the Universe? (3 marks)

I found this question in a past paper but I can't find the mark scheme for it: (Physics P1 Higher Tier. Wednesday 20th June 2012) and it would be really helpful if you could let me know.. Thanks :)

Posted Sun 13th January, 2013 @ 14:31 by Crystal Blue ♥

1 Answer

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Red shift happens because the light waves from distant galaxies is basically stretched. The longer wavelengths of visible light are red and the shorter ones are blue. So distant galaxies appear a red colour, because the wavelength has been stretched.

In order for the light to be stretched, it means that the galaxies must be moving away from us, because as they move away the light is being pulled making the wavelength longer. If the galaxies are moving away from us, it means that they have always been moving away from us. This means that if we reverse this, then all of the galaxies must come together to one single point. If they have always been moving away, they must have started somewhere - the small point which was where the big bang happened.

Answered Sun 13th January, 2013 @ 15:04 by Tilly - Team GR