Red-shift and the expanding universe (physics only)

The graph shows how the red-shift of light from distant galaxies depends on their distance from Earth.

(a) Describe the relationship shown by the graph. [1]

(b) Explain how red-shift provides evidence that the universe is expanding. [2]

(c) Explain how this evidence supports the Big Bang theory. [1]

(d) Observations of distant supernovae made since the late 1990s suggest that the expansion of the universe is speeding up. Name what scientists have proposed to explain this. [1]

This question is about light from distant galaxies.

(a) Complete the sentences. Choose answers from the box. Each word may be used once, more than once or not at all.

faster  |  frequency  |  red-shift  |  refraction  |  slower  |  wavelength

Light from most distant galaxies has an observed increase in __________. [1]

This effect is called __________. [1]

The further away a galaxy is, the __________ it is moving away from us. [1]

(b) Which statement describes the Big Bang theory? Tick (✓) one box. [1]

☐ The universe has always existed and has never changed in size.
☐ The universe began from a very small region that was extremely hot and dense.
☐ The universe began when a large star exploded as a supernova.
☐ The universe is shrinking towards a very small, cold region.

The table shows data for four distant galaxies.

(a) A student says: “The speed of a galaxy is directly proportional to its distance from Earth.”

Use data from the table to show that the student is correct. [2]

(b) A fifth galaxy is 950 million light years from Earth. Predict the speed at which it is moving away from Earth. [1]

(c) Which galaxy, P, Q, R or S, shows the greatest red-shift? Give a reason for your answer. [1]

Andromeda is one of the closest large galaxies to the Milky Way.

The light from Andromeda shows a decrease in wavelength. This effect is called blue-shift.

(a) Suggest what blue-shift tells scientists about the motion of Andromeda relative to the Milky Way. [1]

(b) A student says: “The light from Andromeda proves that the universe is not expanding.”

Explain why the student is wrong. [2]

Astronomers have observed the light from many distant galaxies.

Explain how these observations led scientists to the Big Bang theory, and how observations made since 1998 have changed scientists’ ideas about the universe. [6]

A line in the hydrogen spectrum has a wavelength of 656 nm when measured in a laboratory. In the light from galaxy Z the same line has a wavelength of 679 nm.

For galaxies that are not too far away, the speed $v$ at which a galaxy moves away from Earth can be found using:

$$v = \frac{\text{increase in wavelength}}{\text{laboratory wavelength}} \times c$$

where $c$ is the speed of light, $3.00 \times 10^{5}$ km/s.

(a) Calculate the speed at which galaxy Z is moving away from Earth. [3]

(b) Galaxies move away from Earth at 21 km/s for every million light years of distance.

Calculate the distance to galaxy Z in millions of light years. [1]

(c) In the light from galaxy W, the same line has a wavelength of 702 nm.

Without calculating a speed, estimate the distance to galaxy W. Give a reason for your answer. [1]

The diagram shows dark lines in the spectrum of light from the Sun, measured in a laboratory, and the same pattern of lines in the light from two distant galaxies, X and Y.

(a) Describe how the spectrum of galaxy X is different from the spectrum of the Sun. [1]

(b) What does this difference tell you about the motion of galaxy X? [1]

(c) What can you conclude about galaxy Y compared with galaxy X? Give a reason for your answer. [2]

A line in the spectrum of hydrogen has a wavelength of 486 nm when measured in a laboratory.

In the light from a distant galaxy, the same line is observed at a wavelength of 510 nm.

(a) Calculate the increase in the wavelength of this line. [1]

(b) Write down the equation that links frequency ($f$), wavelength ($\lambda$) and wave speed ($v$). [1]

(c) The speed of light is $3.00 \times 10^{8}$ m/s. 1 nm $= 1 \times 10^{-9}$ m.

Calculate the frequency of the light observed at 510 nm. Give your answer in standard form. [3]

(d) State how the frequency of the light observed from the galaxy compares with the frequency of the same line measured in the laboratory. [1]

Before 1998, many scientists expected that the rate at which the universe is expanding would be decreasing.

(a) Suggest why scientists expected the expansion of the universe to be slowing down. [1]

(b) In 1998, two independent teams of scientists reported observations of light from supernovae in very distant galaxies.

State what these observations suggested about distant galaxies. [1]

(c) Scientists accepted these new observations even though they did not match what was expected.

Explain why. [2]

(d) Scientists do not yet understand what is causing this change in the expansion. Give the name scientists use for it. [1]

A teacher uses a balloon to model the expanding universe.

Three dots, A, B and C, are drawn on the balloon. The balloon is then inflated for 20 s. The diagram shows the distances between the dots before and after inflating.

(a) Calculate the mean speed at which dot B moves away from dot A. [2]

(b) Calculate the mean speed at which dot C moves away from dot A. [1]

(c) Explain how the model shows what scientists observe about the light from distant galaxies. [2]

(d) Give one way in which the balloon is not a good model of the universe. [1]