Cosmology (Edexcel GCSE Physics): Flashcards
Exam code: 1PH0
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Define the Big Bang theory.
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Define the Big Bang theory.
The Big Bang theory states that around 14 billion years ago, the Universe began from a very small, extremely hot and dense region in a giant explosion, and has been expanding and cooling ever since.
Define the Steady State theory.
The Steady State theory states that the Universe has always existed more or less as it is now, with new galaxies forming in the gaps as existing galaxies move apart, keeping the density of galaxies constant.
In the balloon analogy for the expanding Universe, what do the balloon and the dots on its surface represent?
The balloon represents space, and the dots represent galaxies. As the balloon inflates, the dots move further apart because the space itself is expanding.
What happens to the density of galaxies as the Universe expands, according to the Big Bang theory?
The density of galaxies falls, since the number of galaxies stays the same but the space between them increases.
Name the two main pieces of evidence for the Big Bang theory.
Galactic red-shift and Cosmic Microwave Background (CMB) radiation.
Observations of red-shift show that distant galaxies are ______ faster than nearby galaxies, and all galaxies are moving ______ from each other.
Observations of red-shift show that distant galaxies are receding faster than nearby galaxies, and all galaxies are moving away from each other.
True or False?
The Steady State theory can explain the existence of the Cosmic Microwave Background radiation.
False.
The Steady State theory cannot account for the CMB radiation, which is one of the key reasons it is no longer accepted.
Define the Doppler effect.
The Doppler effect is the change in observed frequency and wavelength of waves that occurs when a wave source moves relative to an observer.
How do the wavefronts of a stationary wave source spread out?
Symmetrically, in evenly spaced circles.
What happens to the wavelength and frequency of waves in front of a moving source?
The wavelength decreases and the frequency increases.
What happens to the wavelength and frequency of waves behind a moving source?
The wavelength increases and the frequency decreases.
If the wavelength of a wave source ______, its frequency must ______.
If the wavelength of a wave source increases, its frequency must decrease.
True or False?
A moving wave source causes the wavefronts to become squashed together on one side and stretched out on the other.
True.
Waves in front of the source are squashed (shorter wavelength) and waves behind the source are stretched (longer wavelength).
Define red-shift.
Red-shift is the increase in the wavelength of light from an object moving away from an observer, shifting it towards the red end of the spectrum.
Define blue-shift.
Blue-shift is the decrease in the wavelength of light from an object moving towards an observer, shifting it towards the blue end of the spectrum.
What is the relationship between a galaxy's distance from Earth and the size of its observed red-shift?
The greater the distance to the galaxy, the greater the red-shift, meaning the galaxy is moving away faster.
Why does red-shift provide evidence that the Universe is expanding?
Light waves are stretched by the expansion of space, increasing their wavelength. Since more distant galaxies show greater red-shift, all galaxies must be moving away from each other and from Earth.
Both the Big Bang and Steady State theories can account for the ______ of galaxies, but only the Big Bang theory is supported by the ______ radiation.
Both the Big Bang and Steady State theories can account for the red-shift of galaxies, but only the Big Bang theory is supported by the Cosmic Microwave Background (CMB) radiation.
How does the Steady State theory explain the observed red-shift of galaxies?
It suggests that as galaxies move apart, new galaxies form in the gaps between them, so more distant galaxies still show a greater red-shift even though the Universe stays the same overall.
True or False?
If you traced the expansion of the Universe back in time, the galaxies would become closer together until the whole Universe was a single point.
True.
This is consistent with the Big Bang theory, in which the Universe began from a single, extremely hot and dense point.
Define the Cosmic Microwave Background (CMB).
The CMB is electromagnetic radiation left over from the early, hot and dense stages of the Universe, detected from all directions at a uniform temperature of 2.73 K.
Why is the CMB radiation now found in the microwave region of the spectrum, rather than as high-energy gamma radiation?
The radiation has been red-shifted over about 14 billion years as the Universe expanded, increasing its wavelength from the gamma end of the spectrum into the microwave region.
Why could astronomers not detect the CMB until the development of space flight?
Microwaves are absorbed by the atmosphere, so telescopes had to be sent into orbit above the atmosphere to detect them.
Why does the discovery of the CMB support the Big Bang theory over the Steady State theory?
The CMB has the exact uniform profile expected from a hot body cooling over billions of years, which the Steady State theory cannot explain.
On a CMB temperature map, ______ regions represent a higher density of galaxies, while ______ regions represent a lower density of galaxies.
On a CMB temperature map, warmer (red/orange) regions represent a higher density of galaxies, while cooler (blue/green) regions represent a lower density of galaxies.
True or False?
The temperature of the CMB varies enormously across the sky.
False.
The CMB temperature is mostly uniform, with only minuscule fluctuations of around 0.00001 K.
Give two ways early astronomers used the sky before telescopes existed.
They used the sky for navigation and agriculture, splitting the sky into constellations and aligning monuments with the Sun and Moon to track the seasons.
What was the most important development in the history of astronomy, and roughly when did it occur?
The invention of the astronomical telescope, in the early 17th century.
Give three reasons why modern telescopes provide more data than early telescopes.
They can detect more wavelengths of the EM spectrum, be positioned above the atmosphere, detect weaker signals, have greater magnification, and use computers to process and improve data.
Name three types of electromagnetic radiation that are absorbed by the Earth's atmosphere before reaching the ground.
Near microwaves, far infrared, near ultraviolet, X-rays and gamma rays.
Space telescopes produce ______ images that are unaffected by the atmosphere, but they are much harder to ______ than ground-based telescopes.
Space telescopes produce clearer images that are unaffected by the atmosphere, but they are much harder to repair than ground-based telescopes.
Give two disadvantages of space telescopes compared with ground-based telescopes.
They are much more expensive, much harder to repair, and cannot be made too large since they must fit into a rocket.
True or False?
Moisture and air currents in the atmosphere can distort astronomical observations made from Earth's surface.
True.
Reflection of light from atmospheric moisture causes light pollution, and air currents distort the path of starlight.
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