ConceptCheck 15-1: Because if the universe is infinitely large, then there should be stars in every possible direction you look, resulting in a light night sky instead of a dark night sky.
ConceptCheck 15-2: The spectral shift toward the shorter blue wavelengths means that the Andromeda Galaxy is moving toward our Milky Way Galaxy.
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ConceptCheck 15-3: The two most important observations are that galaxies have redshifted spectra and that the most distant galaxies are moving away from us fastest.
ConceptCheck 15-4: The cosmological principle applies over very large regions of outer space; it does not apply to the distribution of stars in objects as small as a galaxy.
ConceptCheck 15-5: The age of the universe, T0, is calculated as 1/H0; so, if H0 is larger, then T0 must be smaller.
ConceptCheck 15-6: The observable universe becomes larger as more light from never-before-seen distant galaxies has sufficient time to reach us.
ConceptCheck 15-7: The expansion of the universe over the past 13.7 billion years has stretched and redshifted these photons to such a great degree that they are now low-energy, long-wavelength microwave photons.
ConceptCheck 15-8: Earth formed about 4.5 billion years ago, when the universe was about 9 billion years old, and the universe has been dominated by matter for most of its history.
ConceptCheck 15-9: The universe had to be sufficiently cool for atoms to form, so if the early universe was hotter for longer, the first atoms would have appeared more slowly.
ConceptCheck 15-10: The WMAP data shows slight differences in temperature at various locations from which astronomers think were the locations for the initial formation of galaxies and is significantly more detailed than earlier observations.
ConceptCheck 15-11: No. The universe underwent a very brief but dramatic expansion, right after the Big Bang.
ConceptCheck 15-12: The strong nuclear force dominates in the short-distance realm of atomic nuclei.
ConceptCheck 15-13: In a closed universe, any beam of light eventually comes back to its starting point, so in this geometrical sense, Earth is a closed universe.
ConceptCheck 15-14: The slope of the line with value H0 will be shallower for a rapidly expanding universe.
ConceptCheck 15-15: Astronomers must make the assumption that all Type Ia supernovae have identical luminosities, regardless of the galaxy in which they are found.
ConceptCheck 15-16: Today’s universe is dominated by dark energy, followed by matter, and lastly by radiation energy.
CalculationCheck 15-1: Because z = the change in wavelength (λ − λ0) divided by the original λ0, z = (725.6 nm − 656.3 nm) ÷ 656.3 nm = 0.11.
CalculationCheck 15-2: Hubble’s Law, ν = H0d, can be rearranged as d = ν ÷ H0. Using H0 = 73 km/s/Mpc, d = ν ÷ H0 = 10,000 km/s ÷ 73 km/s/Mpc = 134 Mpc (million parsecs).
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