THE DOPPLER EFFECT
3 marks · NormalExplain how the observation of red-shifted light from distant galaxies provides evidence for the Big Bang theory.
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The observation of red-shifted light from nearly all distant galaxies shows that these galaxies are moving away from us, meaning the universe is expanding. If the universe is expanding, it must have started from a much smaller, hotter, and denser state. This expansion from an original point is strong evidence in support of the Big Bang theory, which proposes that the universe began with a massive explosion and has been expanding ever since.
Also accept: Red-shifted galaxies show expansion, implying an origin from a single point
Common mistakes: Not linking expansion to an original starting point; Discussing the Doppler effect without mention of the Big Bang
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Marking points
M1 · 1 mark · States that red-shift shows galaxies are moving away/universe is expanding.
M1 · 1 mark · Implies or states that expansion suggests a starting point or origin.
M1 · 1 mark · Links these arguments to evidence for the Big Bang theory.
Worked solution
Red-shifted light from distant galaxies shows they are moving away from us, meaning the universe is expanding. This suggests it was once smaller and denser, which supports the idea that it began with the Big Bang.