Red Shift And The Expanding Universe P
Übersicht
Hydrogen glowing in a laboratory tube gives out light at a fixed and unmistakable set of wavelengths. Point a telescope at a galaxy so far away that its light left before there were people to look at it, and you find the same set of wavelengths, in the same order, with the same arrangement, sitting in the wrong place. The whole group has slid towards the long end. The hydrogen has not changed. Something happened on the way here.
This lesson is about what that something is, and it is one of the few places in the course where a single measurement leads all the way to a claim about everything that exists. You will start with an ambulance siren, because the same physics runs a siren and a galaxy. You will then learn how to build the argument that takes you from a displaced set of lines to a universe with a beginning, why the careful version of that claim is that space itself is stretching rather than that the galaxies are flying through it, and why a faint hiss of microwaves arriving from every direction at once is the piece of evidence that decided the question.
Ziele
- If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency. This is known as the Doppler effect. Students should understand that: the wave source could be, for example, light, sound or microwaves; when the source moves away from the observer, the observed wavelength increases and the frequency decreases; when the source moves towards the observer, the observed wavelength decreases and the frequency increases.
- There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. This effect is called red shift. The observed red shift suggests that space itself is expanding and supports the Big Bang model (that the universe began from a very small initial point). Students should be able to explain how red shift provides evidence for the Big Bang.
- Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe. It comes from radiation that was present shortly after the beginning of the universe.
- Scientists believe that the universe began with a ‘big bang’, 14 thousand million years ago. The Big Bang theory is currently the only theory that can explain the existence of CMBR.
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- A source of sound moves away from a stationary observer. What happens to the sound observed by the observer? A. The wavelength increases and the frequency decreases B. The wavelength decreases and the frequency increases C. Both the wavelength and the frequency increase D. Both the wavelength and the frequency decrease Answer: A
- What is meant by red shift? A. A decrease in the observed wavelength of light from a distant galaxy B. An increase in the observed wavelength of light from a distant galaxy C. A change in the colour of a star as it becomes hotter D. The absorption of red light by dust between the galaxies Answer: B
- Which statement about cosmic microwave background radiation is correct? A. It is emitted by the nearest stars in our own galaxy B. It is a form of sound that fills the space between galaxies C. It is electromagnetic radiation filling the universe, from radiation present shortly after the beginning of the universe D. It is produced by microwave transmitters on artificial satellites Answer: C
- Spectra observed from many different galaxies show red shift. What have these observations done? A. Proved that the Big Bang theory is correct B. Shown that the Earth lies at the centre of the universe C. Provided further evidence that supports the Big Bang model D. Shown that the space between the galaxies is fixed in size Answer: C
- How long ago do scientists believe the universe began? A. 14 thousand years B. 14 million years C. 14 thousand million years D. 14 million million years Answer: C
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