What red-shift is, why more distant galaxies show more of it, how that supports the Big Bang theory, and what dark matter and dark energy are. Physics only content.
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1.What is red-shift?
An increase in the observed wavelength of light from a source that is moving away from us.
2.What happens to the frequency in red-shift?
It decreases, because the wavelength has increased and the speed of light is unchanged.
3.Why is it called red-shift?
The light is shifted towards the red end of the visible spectrum, which has the longest wavelength.
4.What is observed in light from distant galaxies?
There is a red-shift, showing that they are moving away from us.
5.What is the relationship between distance and red-shift?
The further away a galaxy is, the greater its red-shift.
6.What does a greater red-shift indicate?
The galaxy is moving away faster.
7.What does that relationship tell us about the universe?
That the more distant galaxies are receding faster, which means the universe is expanding.
8.How is red-shift detected?
By looking at the pattern of dark lines in the spectrum of light from a galaxy, and seeing that the whole pattern has shifted towards longer wavelengths.
9.Why is the pattern of lines important rather than the colour alone?
The pattern is fixed for each element, so any shift in it can be measured precisely.
10.Does red-shift mean we are at the centre of the universe?
No. Space itself is expanding, so an observer in any galaxy would see the same pattern of recession.
11.What is the Big Bang theory?
The theory that the universe began from a very small, very hot and very dense region, which has been expanding ever since.
12.What evidence supports the Big Bang theory?
The red-shift of light from distant galaxies, and the cosmic microwave background radiation.
13.What is the cosmic microwave background radiation?
Low level microwave radiation found in all directions in space, left over from the early universe.
14.Why can the Big Bang theory only explain the universe from a moment after it began?
The conditions at the very beginning are not understood, so the theory describes what happened afterwards.
15.How has the accepted model of the universe changed over time?
Improved observations, particularly of supernovae, have shown the expansion is accelerating, which was not expected.
16.What is dark energy?
A proposed form of energy thought to be responsible for the accelerating expansion of the universe.
17.What is dark matter?
Matter that cannot be seen directly but whose gravitational effects on galaxies can be observed.
18.Why do scientists think dark matter exists?
Galaxies rotate faster than the visible matter in them can account for, so there must be additional mass we cannot see.
19.Why is much about the universe still uncertain?
Dark matter and dark energy make up most of the universe but are not understood, so current models are incomplete.
20.What would blue-shift indicate?
That an object is moving towards us, since the wavelength would be shortened.
21.Why is observing distant galaxies also looking back in time?
Light takes a very long time to reach us, so we see those galaxies as they were when the light left them.
22.How do scientific theories like the Big Bang change?
They are modified or replaced when new observational evidence appears that the existing model cannot explain.
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