11.1 Cosmology and particle physics  (Page 8/20)

Explain why it only appears that we are at the center of expansion of the universe and why an observer in another galaxy would see the same relative motion of all but the closest galaxies away from her.

If there is no observable edge to the universe, can we determine where its center of expansion is? Explain.

If the universe is infinite, does it have a center? Discuss.

Another known cause of red shift in light is the source being in a high gravitational field. Discuss how this can be eliminated as the source of galactic red shifts, given that the shifts are proportional to distance and not to the size of the galaxy.

If some unknown cause of red shift—such as light becoming “tired” from traveling long distances through empty space—is discovered, what effect would there be on cosmology?

Olbers’s paradox poses an interesting question: If the universe is infinite, then any line of sight should eventually fall on a star’s surface. Why then is the sky dark at night? Discuss the commonly accepted evolution of the universe as a solution to this paradox.

If the cosmic microwave background radiation (CMBR) is the remnant of the Big Bang’s fireball, we expect to see hot and cold regions in it. What are two causes of these wrinkles in the CMBR? Are the observed temperature variations greater or less than originally expected?

The decay of one type of $K$ -meson is cited as evidence that nature favors matter over antimatter. Since mesons are composed of a quark and an antiquark, is it surprising that they would preferentially decay to one type over another? Is this an asymmetry in nature? Is the predominance of matter over antimatter an asymmetry?

Distances to local galaxies are determined by measuring the brightness of stars, called Cepheid variables, that can be observed individually and that have absolute brightnesses at a standard distance that are well known. Explain how the measured brightness would vary with distance as compared with the absolute brightness.

Distances to very remote galaxies are estimated based on their apparent type, which indicate the number of stars in the galaxy, and their measured brightness. Explain how the measured brightness would vary with distance. Would there be any correction necessary to compensate for the red shift of the galaxy (all distant galaxies have significant red shifts)? Discuss possible causes of uncertainties in these measurements.

If the smallest meaningful time interval is greater than zero, will the lines in [link] ever meet?

Find the approximate mass of the luminous matter in the Milky Way galaxy, given it has approximately ${\text{10}}^{\text{11}}$ stars of average mass 1.5 times that of our Sun.

Find the approximate mass of the dark and luminous matter in the Milky Way galaxy. Assume the luminous matter is due to approximately ${\text{10}}^{\text{11}}$ stars of average mass 1.5 times that of our Sun, and take the dark matter to be 10 times as massive as the luminous matter.

(a) Estimate the mass of the luminous matter in the known universe, given there are ${\text{10}}^{\text{11}}$ galaxies, each containing ${\text{10}}^{\text{11}}$ stars of average mass 1.5 times that of our Sun. (b) How many protons (the most abundant nuclide) are there in this mass? (c) Estimate the total number of particles in the observable universe by multiplying the answer to (b) by two, since there is an electron for each proton, and then by ${\text{10}}^9$ , since there are far more particles (such as photons and neutrinos) in space than in luminous matter.