## Astronomy The Solar System

Physics & Astronomy

## Quiz 22 :

Cosmology

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Q22 Q22 Q22

The figure below shows a graph of the scale factor, R

_{U}, with time, for three different scenarios.The age of the universe is the difference between now and the time at which R_{U}is zero.Which curve illustrates a universe that is expanding at a constant rate?Free

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Multiple Choice

Q62 Q62 Q62

At what temperature would the peak wavelength of blackbody radiation correspond to electron-positron pair production? This would have been the lowest temperature in the early universe at which this effect was common.(Note that a photon's energy is equal to , the cosmic background at any point in time has a blackbody spectrum that peaks at a wavelength , and the mass of a single electron or positron is 9.11 10

^{-31}kg.)Free

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Multiple Choice

Q75 Q75 Q75

The critical mass density of the universe today is 9.5 10

^{}^{27}kg/m^{3}.Using (only) the currently observed amount of luminous matter, what would be the average mass density in the universe? If protons were spread evenly throughout the universe, what would be their typical separation? (Note that the typical separation between protons would be roughly equal to the cubic root of the average volume occupied by one proton, and the mass of a proton is 1.67 10^{}^{27}kg.)Free

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Essay

Q95 Q95 Q95

What was the temperature of the universe when photons were no longer able to spontaneously create proton-antiproton pairs? (Note that a photon's energy is equal to , the cosmic background at any point in time has a blackbody spectrum that peaks at a wavelength , and the mass of a single proton is 1.67 10

^{}^{27}kg.)Free

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