AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Since 1998 onwards, observations of supernovae suggest that distant…
Full specification wording
Red-shift (physics only): Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding ever faster.
Supernovae of one particular type always explode with about the same peak brightness, so astronomers can use them as standard candles: compare how bright one looks with how bright it really is and…
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 6 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Supernovae of one particular type always explode with about the same peak brightness, so astronomers can use them as standard candles: compare how bright one looks with how bright it really is and you get its distance, measured independently of its red-shift. From 1998 onwards those measurements gave a surprise. The most distant supernovae were dimmer, and so further away, than an expansion that was slowing under gravity could account for. The conclusion was that the expansion of the universe is not slowing but accelerating, and that distant galaxies are receding ever faster. Nothing in the existing physics explained it, so the term dark energy was introduced for whatever is driving it. New observations had forced a change of theory.
What earns the marks
- Observations of supernovae being used to measure the distances of very distant galaxies.
- The conclusion that the rate of recession is increasing rather than slowing down.
- Describing this as an accelerating expansion of the universe.
- Naming dark energy as the proposed cause, which is not yet understood.
Common mistakes and how to put them right
Saying that supernovae push the galaxies apart.
Confusing an accelerating expansion with galaxies simply moving away, which was already known.
Claiming that dark energy has been detected directly, when it is a name for an unexplained effect.
Giving a date earlier than 1998 for these supernova observations.
Exam tips
- Quote the date, since the specification names 1998 and questions sometimes ask for it.
- Distinguish moving away from moving away ever faster; only the second is the supernova result.
- Use this example when you are asked how scientists change theories in the light of new evidence.
Try the lesson
The start of the Red-shift (physics only): Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding ever faster. lesson, made from checked teaching notes for this specification point.
Have a go first
What do observations of supernovae since 1998 suggest about distant galaxies?
Listen
Supernovae of one particular type always explode with about the same peak brightness, so astronomers can use them as standard candles: compare how bright one looks with how bright it really is and you get its distance, measured independently of its red-shift. From 1998 onwards those measurements gave a surprise. The most distant supernovae were dimmer, and so further away, than an expansion that was slowing under gravity could account for. The conclusion was that the expansion of the universe is not slowing but accelerating, and that distant galaxies are receding ever faster. Nothing in the existing physics explained it, so the term dark energy was introduced for whatever is driving it. New observations had forced a change of theory. A strong answer earns marks for these points. observations of supernovae being used to measure the distances of very distant galaxies. the conclusion that the rate of recession is increasing rather than slowing down. describing this as an accelerating expansion of the universe. naming dark energy as the proposed cause, which is not yet understood. Exam tip: Quote the date, since the specification names 1998 and questions sometimes ask for it.
Key words
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supernova observations
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measuring distance
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accelerating expansion
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dark energy
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See every definition
- supernova observations
- Observations of supernovae of one particular type, which always explode with about the same peak brightness, used to measure the distances of very distant galaxies.
- measuring distance
- Comparing how bright a supernova looks with how bright it really is gives its distance, measured independently of its red-shift.
- accelerating expansion
- The conclusion that the expansion of the universe is not slowing but accelerating, so distant galaxies are receding ever faster.
- dark energy
- The term introduced for whatever is driving the accelerating expansion, because nothing in the existing physics explained it.
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