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Chapter 34: Frontiers of Physics

College Physics (Urone)
Pages: 1215 - 1240

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57 Questions for Chapter 34: Frontiers of Physics

  1. 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.

    Found on Page 1237
  2. (a) What is the approximate force of gravity on a\({\rm{70 - kg}}\)person due to the Andromeda galaxy, assuming its total mass is\({\rm{1}}{{\rm{0}}^{{\rm{13}}}}\)that of our Sun and acts like a single mass\({\rm{2 Mly}}\)away? (b) What is the ratio of this force to the person’s weight? Note that Andromeda is the closest large galaxy.

    Found on Page 1238
  3. If the smallest meaningful time interval is greater than zero, will the lines in Figure below ever meet?

    Found on Page 1237
  4. Andromeda galaxy is the closest large galaxy and is visible to the naked eye. Estimate its brightness relative to the Sun, assuming it has luminosity\({\rm{1}}{{\rm{0}}^{{\rm{12}}}}\)times that of the Sun and lies\({\rm{2 Mly}}\)away.

    Found on Page 1238
  5. Quantum gravity, if developed, would be an improvement on both general relativity and quantum mechanics, but more mathematically difficult. Under what circumstances would it be necessary to use quantum gravity? Similarly, under what circumstances could general relativity be used? When could special relativity, quantum mechanics, or classical physics be used?

    Found on Page 1237
  6. (a) A particle and its antiparticle are at rest relative to an observer and annihilate (completely destroying both masses), creating two\({\rm{\gamma }}\)rays of equal energy. What is the characteristic\({\rm{\gamma }}\)-ray energy you would look for if searching for evidence of proton-antiproton annihilation? (The fact that such radiation is rarely observed is evidence that there is very little antimatter in the universe.) (b) How does this compare with the\({\rm{0}}{\rm{.511 MeV}}\)energy associated with electron-positron annihilation?

    Found on Page 1238
  7. Does observed gravitational lensing correspond to a converging or diverging lens? Explain briefly.

    Found on Page 1237
  8. The average particle energy needed to observe unification of forces is estimated to be\({\rm{1}}{{\rm{0}}^{{\rm{19}}}}{\rm{ GeV}}\). (a) What is the rest mass in kilograms of a particle that has a rest mass of\({\rm{1}}{{\rm{0}}^{{\rm{19}}}}{\rm{ GeV/ }}{{\rm{c}}^{\rm{2}}}\)? (b) How many times the mass of a hydrogen atom is this?

    Found on Page 1238
  9. Suppose you measure the red shifts of all the images produced by gravitational lensing, such as in figure below. You find that the central image has a red shift less than the outer images, and those all have the same red shift. Discuss how this not only shows that the images are of the same object, but also implies that the red shift is not affected by taking different paths through space. Does it imply that cosmological red shifts are not caused by traveling through space (light getting tired, perhaps)?

    Found on Page 1237
  10. The peak intensity of the CMBR occurs at a wavelength of\({\rm{1}}{\rm{.1 - mm}}\). (a) What is the energy in eV of a\({\rm{1}}{\rm{.1 - mm}}\)photon? (b) There are approximately\({\rm{1}}{{\rm{0}}^{\rm{9}}}\)photons for each massive particle in deep space. Calculate the energy of\({\rm{1}}{{\rm{0}}^{\rm{9}}}\)such photons. (c) If the average massive particle in space has a mass half that of a proton, what energy would be created by converting its mass to energy? (d) Does this imply that space is “matter dominated”? Explain briefly.

    Found on Page 1238

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