Which of the below statements about the CMB are true?
(i) The “hot” and “cold” spots are areas where photons have slightly more or less energy than average.
(ii) It shows that the Universe was accelerating at the time the CMB formed, thus measuring dark
energy early in the Universe.
(iii) The “hot” and “cold” spots were caused by sound waves created from photon pressure because
of slight density variations. If inflation is true, these density variations are a result of quantum
fluctuations during inflation.
(iv) The CMB power spectrum gives information on the overall shape (geometry) of the Universe.
(a) (i), (ii), and (iii)
(b) (i) and (iii)
(c) (i), (iii), and (iv)
(d) (i), (ii), (iii), and (iv)
The correct answer is (c) (i), (iii), and (iv). Let's break down the statements to understand why.
(i) The statement "The 'hot' and 'cold' spots are areas where photons have slightly more or less energy than average" is true. The temperature fluctuations observed in the cosmic microwave background (CMB) are directly related to density fluctuations in the early universe. These fluctuations cause slight differences in photon energies, leading to the formation of hot and cold spots in the CMB.
(ii) The statement "It shows that the Universe was accelerating at the time the CMB formed, thus measuring dark energy early in the Universe" is incorrect. The CMB primarily provides information about the conditions of the universe shortly after the Big Bang, such as the temperature, density, and composition. It does not directly measure dark energy, which was discovered much later.
(iii) The statement "The 'hot' and 'cold' spots were caused by sound waves created from photon pressure because of slight density variations. If inflation is true, these density variations are a result of quantum fluctuations during inflation" is true. During the early stages of the universe, density variations created fluctuations in the photon pressure, leading to the formation of sound waves. These variations in density are thought to have originated from quantum fluctuations during the inflationary period of the universe.
(iv) The statement "The CMB power spectrum gives information on the overall shape (geometry) of the Universe" is true. The CMB power spectrum, obtained from analyzing the temperature fluctuations in different angular scales, provides valuable information about the overall geometry of the universe. Specifically, it helps determine whether the universe is flat, open, or closed.
Therefore, the correct answer is (c) (i), (iii), and (iv).