Astronomers on Earth measure the red-shift of light from two galaxies in different directions. Using measured distances and speeds of galaxies, they also calculate the red-shifts that an observer in a distant galaxy, Galaxy K, would measure for two other galaxies.
| Result | Observer | Distance of target galaxy from observer in million light-years | Fractional red-shift |
|---|---|---|---|
| E | Earth (measured) | 360 | 0.024 |
| E | Earth (measured) | 900 | 0.060 |
| K | Galaxy K (calculated) | 450 | 0.030 |
| K | Galaxy K (calculated) | 1350 | 0.090 |
The astronomers also detect a faint signal from every direction in the sky, including regions with no visible stars or galaxies.
| Result | Wavelength at maximum intensity in mm | Maximum difference in intensity between directions in % |
|---|---|---|
| M | 1.10 | 0.002 |
An astronomer makes this claim:
‘Result E shows that the Earth is at the centre of the expansion of the Universe. This red-shift is the evidence that shows the Big Bang theory is correct and the Steady State theory is wrong. Result M does not help us to choose between the two theories.’
Explain how far the results support the astronomer's claim, and why the Big Bang theory is the currently accepted model for the origin of the Universe.
94 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.