The oldest photons we detect in the universe come from a. distant quasars b. the
ID: 1566833 • Letter: T
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The oldest photons we detect in the universe come from a. distant quasars b. the first generations of stars. c. the most distant galaxies. d. the epoch of recombination. e. the first supernovae. The cosmic microwave background radiation was emitted when the universe had a size about 1/1000 of today's value. What was temperature of the microwave radiation at the epoch of recombination? a. 30 K b. 300 K c. 3000 K. d. 30.000 K e. 300,000 K The existence of the cosmic background radiation tells us that the early universe was a. much hotter than it is today. b. much colder than it is today. c. composed entirely of radiation at early times. d. composed entirely of stars at early times. e. about the same temperature as today but much more dense. After the Big Bang, as the universe cooled and protons and electrons combined, what important consequence happened? a. Protons and neutrons combined to form nuclei such as deuterium and helium. b. Neutrinos ceased to interact with normal matter, c. Dark matter ceased to interact with normal matter. d. Photons began to travel freely through the universe. e. Lithium and other light elements were formed by the fusion of hydrogen and helium. Choose the incorrect statement about the CMB. a. It is nearly isotropic. b. It is a fundamental confirmation of the Big Bang theory. c. It is a thermal signature described by a temperature of about 3K. d. It was discovered accidentally in the 1960s. c. It is thought to be produced by the first generations of stellar black holes. The CMB can be regarded a "wall" beyond which we cannot see because a. photons as hot light b. couldn't leave the before the period. c. haven't the technology to detect light from earlier epochs. d. galaxies absorb all the photons from earliest times, closer to the Big Bang. e. there existed only massive particles within the universe in the first 380,000 years of existence and no photons. e. behind the CMB "Wall" there is a huge black hole that doesn't allow light to escape.Explanation / Answer
20) The oldest photons probably must be from the earliest of stars presemt in the universe. Photon is an elementary particle of light. Hence the first light source will possess the oldest of the photons. Hence it is option (b)
21) The present temperature is 2.725 K. The Temperature is inversely proportional to the size of the universe. Hence At the time of recoombination, the size was 1000 times lesser. Hence the temperature is 1000 times higher than now. Hence the right answer is option (c)=3000 K
22) The early universe was much hotter as well as denser than the present. Looking at the options, option (a) seems to be the best fit for the fact.
23) Before when the protons and electrons were all separate, there were no neutral elements and all the particles in the universe was ionised and possessed a charge. Photons found it difficult to travel as it collided with the charged particles and its path was always obstructed. Photons had been interacting with the ionised particles and hence could not be well seen. Hence the universe was more or less opaque back then. Now the universe is transparent as there is not much ionised particles in the path of the photons. Hence to be precise, option (d) is the right answer.
24) Option (e) is the incorrect answer. Stellar black holes are formed due to the gravitational collapse of a huge star. These are not the origin of the CMBR.
25) (a). The photons couldn't leave the hot plasma before recombination. Hence we couldn't detect any light particle behind CMBR because th photons were interactive with the ionised plasma and not free to travel and to be detected by our telescopes.
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