Cosmology Flashcards
All 30 cards in this deck
What does the Big Bang theory say about the origin of the Universe?
The Universe began from a single point in a huge explosion/expansion and has been expanding ever since.
What does the Steady State theory say about the Universe?
The Universe has always existed, is expanding, and new matter is created as it expands so its appearance/density stays the same.
Name one thing the Big Bang and Steady State theories agree on.
Both say the Universe is expanding.
Give one key difference between the Big Bang and Steady State theories.
Big Bang says the Universe had a beginning; Steady State says it has always existed (with new matter continuously created).
Which theory of the origin of the Universe is currently accepted, and why?
The Big Bang theory, because there is more evidence supporting it than the Steady State theory.
True or false? The Steady State theory cannot explain the red-shift of galaxies.
False. Steady State also has an expanding Universe, so it explains red-shift; it cannot explain the CMB radiation.
What is the Doppler effect?
The change in observed frequency and wavelength of a wave when the source moves relative to the observer.
What happens to the observed wavelength and frequency when a wave source moves away from an observer?
Observed wavelength increases and observed frequency decreases.
What happens to the observed wavelength and frequency when a wave source moves towards an observer?
Observed wavelength decreases and observed frequency increases.
Why does the siren of an ambulance sound lower in pitch as it drives away from you?
The observed frequency is decreased (wavelength increased) because the source is moving away — the Doppler effect.
True or false? The Doppler effect changes the speed of the waves travelling to the observer.
False. The wave speed stays the same; only the observed wavelength and frequency change.
True or false? The Doppler effect happens for light as well as for sound.
True. Light from a moving source shows a change in observed wavelength and frequency, e.g. red-shift.
What is red-shift?
An increase in the observed wavelength (decrease in frequency) of light from an object moving away from us.
What happens to the absorption lines in the spectrum of a galaxy that is moving away from Earth?
They move towards the red end of the spectrum compared with the same lines measured on Earth.
How does the red-shift of a galaxy depend on its distance from Earth?
The further away the galaxy, the greater its red-shift.
What does a large red-shift tell you about a galaxy's recession velocity?
It is moving away from us at a high speed — the bigger the red-shift, the faster the recession velocity.
Why is the red-shift of galaxies evidence that the Universe is expanding?
Almost all galaxies are moving away from us and from each other, and the most distant move fastest — so space itself is expanding.
True or false? Red-shift shows that the Earth is at the centre of the Universe because all galaxies move away from us.
False. Galaxies are moving away from each other everywhere; every observer would see the same red-shift.
What does CMB stand for?
Cosmic Microwave Background (radiation).
What is cosmic microwave background radiation?
Low-energy microwave radiation that comes from all directions in space, left over from the Big Bang.
How does CMB radiation provide evidence for the Big Bang theory?
The Big Bang was an initial explosion that released radiation, which has spread out and is still detected today.
Why did the discovery of CMB radiation make the Big Bang the accepted model?
The Big Bang theory can explain the CMB but the Steady State theory cannot, so Big Bang had more supporting evidence.
True or false? CMB radiation is only detected when telescopes point towards the centre of our galaxy.
False. CMB radiation is detected coming from all directions in space.
True or false? CMB radiation was predicted before it was discovered.
True. The Big Bang theory predicted leftover radiation, which was later detected as microwaves.
How were the stars and planets first observed, before telescopes were invented?
With the naked eye.
What advantage do telescopes have over the naked eye for observing the Universe?
They collect more light, so fainter and more distant objects can be seen in greater detail.
Apart from visible light, name two types of electromagnetic radiation used by modern telescopes to observe the Universe.
Any two of: radio, microwave, infrared, ultraviolet, X-ray, gamma.
Why are some telescopes placed outside the Earth's atmosphere?
The atmosphere absorbs much of the radiation (e.g. X-rays, UV, some infrared) and distorts/blurs the light that does get through.
Give one advantage, other than the atmosphere absorbing radiation, of a space telescope over a ground-based one.
No light pollution or cloud, and no atmospheric distortion, so images are clearer.
True or false? All types of electromagnetic radiation from space reach the Earth's surface.
False. The atmosphere absorbs much of it, e.g. X-rays and most ultraviolet, so those telescopes must be in space.