GCSE · Physics · AQA · Spec 8463
Red-shift and the Big Bang
Almost everything we know about distant galaxies comes from their light. And light from most of them arrives stretched out, with an increased wavelength.
Red-shift
View
now switch to the further galaxy
This galaxy is moving away from us. Line up the first peaks: the blue peaks are further apart than the grey ones, so the light arrives with its wavelength increased. That increase is red-shift.
Not to scale. Grey: light with no red-shift. Blue: the light we actually observe from the galaxy.
From stretched light to the Big Bang
Reason it through
How does stretched light from distant galaxies end up as evidence for the Big Bang theory?
First link · your turn
Start with what is actually measured. What do we notice about the light from most distant galaxies?
Physics · How science works
Observed, concluded, or still a mystery?
Where does each statement belong: something observed, a theory or conclusion drawn from observations, or something still not understood?
Still to sort
Observed (0)
Measured or seen by scientists.
Where the line is: An observation is what was measured. A conclusion is what scientists decide the measurements mean.
Theory or conclusion (0)
What scientists concluded from the observations.
Where the line is: A theory is built on observations and supported by them. It isn't something anyone measured directly.
Still not understood (0)
Things scientists have named but can't yet explain.
Where the line is: Having a name for something is not the same as understanding it.
Scientists use observations to arrive at theories. Sort each statement to see which is which.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Red-shift, and how one pattern in that stretch became evidence for the Big Bang.
What you need to know
- Red-shift: an observed increase in the wavelength of light from most distant galaxies, which are moving away from us.
- Further galaxy → moving faster → bigger increase in wavelength.
- That change of speed with distance is evidence that space itself is expanding, and supports the Big Bang theory.
- Know which statements are observations, which are theories built on them, and what is still not understood (dark mass, dark energy).
The big picture
Light from most distant galaxies is observed with an increased wavelength. This is red-shift. The further away the galaxy, the faster it is moving and the bigger the increase. That change of speed with distance is evidence that space itself is expanding, and the observed red-shift supports the Big Bang theory: the universe began from a very small region that was extremely hot and dense. Since 1998, supernova observations have suggested that distant galaxies are receding ever faster. Much is still not understood, such as dark mass and dark energy.
Key points
Worked example
Problem
A news headline reads: "Astronomers watch galaxies turn red as the universe grows." Rewrite it so that it is scientifically accurate, and explain each change you make.
⚠ Watch out
Treating red-shift as a colour: "the galaxy has turned red". Red-shift is an observed increase in the wavelength of the light. The other trap is getting the pattern backwards: the bigger increase comes from the galaxies that are further away, not the nearer ones.
Memory hook
Far, fast, stretched. The further the galaxy, the faster it moves away and the more its light is stretched. A universe where that is true is an expanding one.
Check yourself
Cover the page. What is red-shift, how does it change with a galaxy's distance, and which theory does it support? Then name one thing still not understood.
Flashcards
(11)What is red-shift?
Is red-shift seen in light from galaxies moving towards us or away from us?
Does red-shift mean a galaxy is red?
How does the size of the red-shift change with a galaxy's distance?
How does a galaxy's speed change with its distance from us?
What is the change of each galaxy's speed with distance evidence of?
Which theory does the observed red-shift support?
According to the Big Bang theory, how did the universe begin?
What have observations of supernovae suggested since 1998?
How do scientists arrive at theories such as the Big Bang theory?
Give two examples of things about the universe that are still not understood.
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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