8.4 Red-shift and the Big Bang
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What does the red-shift of the light from a distant galaxy show?
Choose one answer.
Correct Not quite: the answer is The galaxy is moving away from us
Mark scheme
B: The galaxy is moving away from us
Model answer
The galaxy is moving away from us (B).
State what is meant by red-shift.
Mark scheme
the wavelength of the light from a source is increased (1); because the source is moving away from the observer (1)
Model answer
The wavelength of light from a source moving away from us is stretched and moved towards the red end of the spectrum.
Describe what astronomers find when they compare the spectrum from a distant galaxy with the same spectrum in a laboratory.
Mark scheme
the same pattern of dark lines (1); but shifted towards longer wavelengths / the red end (1)
Model answer
They see the same pattern of dark lines, but all of them are shifted to longer wavelengths.
Galaxy A has a larger red-shift than galaxy B. State what this shows about the distance of each from us, and how fast each is moving.
Mark scheme
galaxy A is further away (1); galaxy A is moving away faster (1); both are moving away from us (1)
Model answer
Galaxy A is further away from us and is moving away faster than galaxy B. Both are moving away.
Explain how red-shift provides evidence that the Universe is expanding.
Mark scheme
nearly all galaxies show red-shift, so they are moving away (1); the further away the galaxy, the greater the red-shift (1); so the further galaxies move away faster, as in an expanding space (1)
Model answer
Almost all galaxies are red-shifted, so they are moving away from us, and the more distant ones have bigger red-shifts. This is what we would expect if the Universe is expanding.
Describe the Big Bang theory.
Mark scheme
the Universe began from a very small / hot / dense region (1); it expanded rapidly (1); about 13.8 billion years ago, and it is still expanding (1)
Model answer
The Universe began from a very small, hot and dense region and has been expanding ever since, about 13.8 billion years ago.
Explain what the cosmic microwave background radiation is, and why it supports the Big Bang theory.
Mark scheme
radiation from the early hot Universe (1); its wavelength has been stretched into the microwave region as the Universe expanded (1); the Big Bang theory predicted it / it comes from all directions equally (1)
Model answer
It is radiation left over from the early Universe, whose wavelength has been stretched into the microwave region by the expansion. The Big Bang theory predicted it, so it supports the theory.
State why most scientists no longer accept the Steady State theory.
Mark scheme
it cannot explain the CMBR (1); the Big Bang theory explains all of the evidence (1)
Model answer
The Steady State theory cannot explain the cosmic microwave background radiation, while the Big Bang theory explains all the evidence.
(AQA) State what dark matter and dark energy are thought to explain.
Mark scheme
dark matter: extra gravity needed to explain the rotation of galaxies (1); dark energy: the expansion of the Universe speeding up / accelerating (1)
Model answer
Dark matter explains why galaxies rotate faster than the visible matter can account for. Dark energy explains why the expansion of the Universe is speeding up.
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