4.3 : Cosmology

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Our understanding of modern cosmology has developed from...
Edwin Hubble's discovery that the Universe is expanding.
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What is the Doppler Effect?
The principle that when we receive waves from sources that are moving relative to us, their wavelength is variable. This causes blueshift (an increased wavelength of approaching waves) and redshift (a decreased wavelength of departing waves).
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What can the Doppler Effect determine about a certain galaxy?
Whether it is moving towards or away from us.
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How is the change of wavelength of a spectral line related to the galaxy's radial velocity?
(Observed wavelength of spectral line - true wavelength of spectral line)/(true wavelength of spectral line) = (radial velocity)/(speed of light).
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How is the Doppler Effect evidence for the Universe's expansion?
Since all distant galaxies exhibit redshift, they are moving away and therefore the Universe is expanding.
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What is Hubble's Law?
The recession velocity of a galaxy is proportional to its distance from us -- v = Hd, where H is Hubble's constant.
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What does the Universe's expansion imply about the beginning of the Universe?
The Universe began as an extremely small initial point. This extremely small, dense and hot 'singularity' expanded rapidly in the Big Bang.
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What is the believed age of the Universe and how was it interpreted?
It was found by inverting Hubble's constant (unit: per second) to give a value of 13.8 billion years.
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What is the Solid State theory?
The theory models an expanding Universe with matter being constantly created so that the overall density of the Universe remains constant. There is no observational evidence for this.
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What is the Cyclic Universe theory?
The theory suggests that there have been a series of Big Bang/Big Crunch scenarios and that these will continue in the future. This lacks hard evidence.
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What is one of the main pieces of evidence for the Big Bang theory?
The existence of cosmic microwave background (CMB) radiation that pervades the Universe and perfectly matches the radiation emitted by a 'black body' with a temperature of 2.7K.
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How can CMB radiation be observed?
As a faint background 'glow' of radiation at microwave wavelengths in the space between galaxies, which merely appears black through the eye of an optical telescope.
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How was CMB radiation discovered and by who?
Arno Penzias and Robert Wilson were attempting to detect faint reflections of radio waves from Echo balloon satellites at the Bell Laboratories in Holmdel, New Jersey using a giant horn radio antenna, which picked up a steady uniform 'noise' -- CMB.
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How does CMB provide evidence for the Big Bang theory?
George Gamow predicted that if the Universe was extremely hot and dense, it would now have cooled (as it expanded) to a temperature just a few degrees above absolute zero. This matched the temperature of CMB radiation.
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What was NASA's COsmic Background Explorer (COBE) satellite used for and what does its findings suggest about the early Universe?
The satellite used very sensitive detectors to study CMB. It confirmed the uniform nature (isotropy) of CMB on a large scale, but also detected minute fluctuations. This data aided the study of the distribution of energy/matter in the early Universe.
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What did the Wilkinson Microwave Anisotropy Probe (WMAP), COBE's successor, discover?
It studied CMB in greater detail and also provided data that enabled cosmologists to estimate the contribution of dark matter in the Universe and to confirm the existence of dark energy.
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What is dark matter and what could it include?
Matter that is invisible to astronomers (it does not emit or reflect radiation) but has detectable gravitational effects. It could include black holes, neutrinos and Weakly Interacting Massive Particles (WIMPs).
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Why was dark matter first proposed?
It was proposed as an explanation for stars at large distance from the central nucleus were observed to be travelling much faster than expected, given the mass of the central nucleus. The galaxy must have contained a great deal of 'invisible mass.'
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What is gravitational lensing and how can it be explained by the existence of dark matter?
This is where images of the same galaxy are distorted by the gravitational pull of a huge amount of matter. Dark matter provides a source of this matter.
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How much of the total mass of the Universe is believed to be dark matter?
90%.
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What is the 'Big Crunch'?
The contraction of the Universe after it has exceeded a 'critical density.'
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How does dark energy cause the acceleration of the Universe's expansion?
It provides a mysterious repulsive force of 'negative' gravity, observed from distant supernovae.
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Other cards in this set

Card 2

Front

What is the Doppler Effect?

Back

The principle that when we receive waves from sources that are moving relative to us, their wavelength is variable. This causes blueshift (an increased wavelength of approaching waves) and redshift (a decreased wavelength of departing waves).

Card 3

Front

What can the Doppler Effect determine about a certain galaxy?

Back

Preview of the front of card 3

Card 4

Front

How is the change of wavelength of a spectral line related to the galaxy's radial velocity?

Back

Preview of the front of card 4

Card 5

Front

How is the Doppler Effect evidence for the Universe's expansion?

Back

Preview of the front of card 5
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