CosmologyEdexcel GCSE Physics: Flashcards

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What is red-shift?

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What is red-shift?: An increase in the observed wavelength (and decrease in frequency) of light from a source moving away from the observer.
What causes red-shift and blue-shift?: The Doppler effect — relative motion between a wave source and an observer changes the observed frequency and wavelength.
What is the relationship between a galaxy's distance and its red-shift?: The further away a galaxy is, the greater its red-shift, meaning it is moving away faster.
What does red-shift of distant galaxies provide evidence for?: That the Universe is expanding.
State the Big Bang theory.: The Universe began from an extremely hot, dense point and has been expanding and cooling ever since.
State the Steady State theory.: The Universe has always existed and always looks the same, with new matter continuously created as it expands.
Can both the Big Bang and Steady State theories explain red-shift?: Yes — both involve an expanding Universe, so both predict red-shift of distant galaxies.
What is cosmic microwave background (CMB) radiation?: Faint radiation detected uniformly from all directions in space, interpreted as leftover radiation from the hot early Universe.
Why did the discovery of CMB radiation support the Big Bang theory?: The Big Bang theory predicted this leftover radiation, but the Steady State theory had no convincing explanation for it.
Why is the Big Bang theory currently the accepted model?: Because there is more evidence supporting it (red-shift and CMB radiation) than the Steady State theory.
If a galaxy is moving away from Earth, is its light red-shifted or blue-shifted?: Red-shifted — its wavelength increases and frequency decreases.
What evidence for the Big Bang is 'limited to' according to the spec?: Red-shift of galaxies and cosmic microwave background (CMB) radiation.