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  ASTR 2010 Modern Cosmology Spring 2022: Clicker Questions

Tue 2022 Mar 29:

1. The units of the Hubble constant \(H_0\) are 1/time. What fundamental property of the Universe does that time, \(1/H_0\), measure?
   A. The smallest possible time, a Planck time, \(\sqrt{G \hbar / c^5} \approx 10^{-43}\) seconds.
   B. The period of rotation of the Earth, 1 day.
   C. The orbital period of the Earth, 1 year.
   D. The age of the Solar System, 4.6 billion years.
   E. The age of the Universe, 14 billion years.
2. What is the largest region around us that has turned around from the Hubble expansion, and is not expanding?
   A. The Solar System.
   B. The Milky Way.
   C. The Local Group of galaxies.
   D. The Local Supercluster of galaxies.
   E. The observable Universe.
   
3. Why does \(1/H_0\) not exactly measure the age of the Universe?
   A. Because measurements of the Hubble constant have some uncertainty.
   B. Because Hubble's law applies only to distant galaxies.
   C. Because the Universe has decelerated and/or accelerated since the Big Bang.
   
4. What does the symbol \(\Omega\) (the last letter of the Greek alphabet) signify in cosmology?
   A. The size of the Universe.
   B. The age of the Universe.
   C. The rate of expansion of the Universe.
   D. The rate of acceleration of the Universe.
   E. The ratio of the actual mass-energy density of the Universe to the critical density required to make it spatially flat.
   

Th 2022 Mar 31:

5. The announcement in 1998 of what remarkable observation ushered in the Standard ΛCDM Model of Cosmology?
   A. The Universe is expanding.
   B. The Universe is accelerating.
   C. The Universe contains Dark Matter.
   D. The detection of microwaves from the early Universe.
   E. The Universe has a flat spatial geometry.
   
6. Why was it necessary to use a satellite (COBE) to obtain a clear view of the Cosmic Microwave Background?
   A. Because the CMB comes from so far away.
   B. Because astronomers observing from the ground would be cooked by microwaves.
   C. Because water vapor in the atmosphere absorbs microwaves.
   D. Because of interference from TV and other microwave communications.
   E. Because scientists are in cahoots with NASA to fly big expensive missions.
7. What thing in the room you are sitting in is closest to thermodynamic equilibrium? (What does thermodynamic equilibrium mean? Answer: An equilibrium state in which there are no macroscopic flows of energy, momentum, particles, or other conserved quantities.)
   A. Your brain.
   B. Your body.
   C. The lights.
   D. The air conditioning.
   E. The air.

The CMB was released at “Recombination,” when hydrogen in the Universe went from being ionized and opaque, to neutral and transparent, at a temperature of about 3000 Kelvin. The temperature of the CMB today is about 3 Kelvin. As the Universe expanded, its scale factor \(a\) increased, the wavelength \(\lambda\) of CMB photons were stretched by the expansion, and the temperature \(T\) of the CMB decreased correspondingly, \(T \propto 1/\lambda \propto 1/a\).

8. By what factor has the Universe expanded since Recombination?
   A. \(10^{-3}\).
   B. \(1\).
   C. \(10^3\).
   D. \(10^6\).
   E. \(10^{12}\).

Tue 2022 Apr 5

9. Which of the following statements about the Cosmic Microwave Background (CMB) is true?
   A. It is remarkably uniform, showing temperature fluctuations of a few \(10^{-5}\).
   B. It has an exquisitely accurate thermal (blackbody) spectrum at a temperature of 2.7255 Kelvin.
   C. It comes to us from the time of “Recombination,” when hydrogen in the Universe went from being ionized and opaque, to neutral and transparent, at a temperature of about 3000 Kelvin.
   D. It comes to us from when the Universe was 400,000 years old.
   E. All of the above.
10. What set the characteristic scale (spatial length) of fluctuations in the CMB?
    A. Quantum fluctuations at the Big Bang.
    B. Gravity.
    C. The wavelength of light waves (photons) at Recombination.
    D. The horizon size (about 400,000 lightyears) at Recombination.
11. Classroom Task 6: Science vs. Pseudoscience. Shall we do it?
    A. Yes.
    B. No.
    How can we decide whether the power spectrum of the CMB is real, not a fake made up by scientists?
12. Gravity causes galaxies to cluster.
    A. True.
    B. False.
13. The characteristic scale of galaxy clustering (about 100 Mpc, or 300 Mlyr, a supercluster scale) was set by the scale of clustering seen in the Cosmic Microwave Background.
    A. True.
    B. False.

Th 2022 Apr 7

14. The tiny temperature fluctuations seen in the Cosmic Microwave Background grew by gravity into the large scale structures that we see today: galaxies, clusters of galaxies, and superclusters of galaxies.
    A. True.
    B. False.
15. The characteristic scale of the tiny fluctuations in the CMB is \(1^\circ\), corresponding to the horizon size (400,000 lightyears) at Recombination. That scale corresponds to what scale today?
    A. The size of a solar system.
    B. The size of a galaxy.
    C. The size of a Local Group of galaxies.
    D. The size of a supercluster of galaxies.
    E. The size of the observable Universe.
16. Most of the “baryonic” (i.e. atomic) matter in the Coma rich supercluster of galaxies is in:
    A. Planets.
    B. Stars.
    C. Hot intergalactic (10⁸ Kelvin) gas.
    D. Non-baryonic Dark Matter.
    E. Dark Energy.
17. What do you see in this image of the Abell 1689 supercluster of galaxies?
    A. Stars, the bright points with cross-hair diffraction spikes indicating that they are unresolved.
    B. Yellowish blobs, which are are galaxies in the galaxy cluster.
    C. Bluish arcs, which are background galaxies lensed by the galaxy cluster.
    D. Darkness between the bright stars and galaxies.
    E. All of the above.
    
18. What is the best astronomical evidence for non-baryonic dark matter?
    A. Laboratory detection of dark matter.
    B. Galaxy rotation curves.
    C. Dark matter in clusters of galaxies deduced from gravitational lensing.
    D. The Bullet cluster.
    E. The power spectrum of the CMB requires non-baryonic cold dark matter.

Tue 2022 Apr 12

19. A team of astronomers tentatively claim to have detected a galaxy at redshift of \(z = 13\). By what factor has the Universe expanded since the galaxy emitted its light?
    A. 12.
    B. 13.
    C. 14.
    D. This question has no definite answer.
    
20. What is the main evidence that the Universe today is currently accelerating?
    A. The Hubble diagram of high redshift Type Ia (thermonuclear) supernovae.
    B. The power spectrum of temperature fluctuations in the Cosmic Microwave Background.
    C. The clustering of galaxies.
    D. The ages of the oldest stars.
    E. This question has no definite answer.
    
21. Are the fundamental laws of physics the same at different times?
    A. Yes.
    B. No.
    What is the evidence for that?
22. Are the fundamental laws of physics the same at different places?
    A. Yes.
    B. No.
    What is the evidence for that?

Th 2022 Apr 14

23. The tiny temperature fluctuations seen in the Cosmic Microwave Background grew by gravity into the large scale structures that we see today: galaxies, clusters of galaxies, and superclusters of galaxies.
    A. True.
    B. False.
24. The Hubble diagram of high redshift Type Ia (thermonuclear) supernovae shows that the Universe today is accelerating. In general relativity, gravitational acceleration is proportional to \(- ( \rho + 3 p )\). Which of the following kinds of energy is gravitationally repulsive?
    A. Radiation (relativistic stuff), \(p = \tfrac{1}{3} \rho\).
    B. Matter (non-relativistic stuff), \(p = 0\).
    C. Curvature, \(p = - \tfrac{1}{3} \rho\).
    D. Vacuum, \(p = - \rho\).
25. The expansion problem is: Why is the Universe expanding? Why is this a problem?
26. The horizon problem is: How can parts of the CMB more than about 1° apart have almost the same temperature? Why is this a problem?

Tue 2022 Apr 19

27. Jocelyn Bell and her academic advisors in 1967 concluded that the radio pulses they were receiving were not aliens (Little Green Men). Why not?
    A. Because the signal was far too bright.
    B. Because the signal did not vary in a way that a message would.
    C. Because the signal was coming through at many radio frequencies, and LGM would have concentrated on one frequency.
    D. Because LGM is just a crazy idea.
28. The gravitationally repulsive Dark Energy seen in today's Universe appears to have the properties of vacuum energy (\(p = -\rho)\). Is the Dark Energy the same as the vacuum energy hypothesized to drive inflation?
    A. Yes.
    B. No.
29. Is it likely that more of our Universe lies beyond our horizon?
    A. Yes.
    B. No.
30. A plucked guitar string carries several frequencies (harmonics). Is it true that lower frequencies take a longer time for the string to oscillate?
    A. True.
    B. False.

Tue 2022 Apr 26

31. Which of the following is not observational evidence for the Standard ΛCDM Model of Cosmology?
    A. The Hubble diagram of high redshift Type Ia (thermonuclear) supernovae.
    B. The clustering of galaxies.
    C. The power spectrum of temperature fluctuations in the Cosmic Microwave Background.
    D. The abundance of light elements H, He, D, and Li.
    E. The 4.6 Gyr age of the solar system.

Th 2022 Apr 28:

32. Is Hawking radiation visible to an observer inside the horizon of a black hole?
    A. Yes.
    B. No.
33. Is the singularity of the ideal mathematical solution for a Reissner-Nordström black hole gravitationally attractive or repulsive (what does the river model for RN black holes say)?
    A. The singularity is gravitationally attractive.
    B. The singularity is gravitationally repulsive.
34. From the point of view of an observer outside the outer horizon of a white hole, is the white hole gravitationally attractive or repulsive?
    A. The white hole is gravitationally attractive.
    B. The white hole is gravitationally repulsive.
35. Would you vote in favor of making a baby Universe?
    1 A. I think that it is immoral to attempt to make a baby Universe. I vote no.
    3 B. If this is the only way that our Universe can reproduce, then I think society has a moral duty to make it happen. I vote yes.
    1 C. I don't think society should waste resources attempting to make a baby Universe. I vote no.
    3 D. I don't have a strong moral opinion, but I support the notion that society should attempt to make a baby Universe. I vote yes.
    0 E. I don't really care either way. I probably won't bother to vote.
36. If society were presented with the one-time opportunity to make a baby Universe, what do you think the eventual outcome would be?
    6 A. All out war between the yes and no factions.
    0 B. Fierce political discussion, resolved by the democractic process.
    1 C. Fierce political discussion, leading to deadlock.
    1 D. Nothing. Society would not care, and would just go about its business.
    0 E. C, but the hero and heroine wade in and break the deadlock.
37. You are the leader of the “No-baby-Universe” faction. You believe deeply that your cause is right. You strive for right. But your faction has lost the vote. What do you do?
    3 A. Continue to argue non-violently for your cause.
    4 B. Fight for right. Start a guerilla war.
    1 C. Spread disinformation about your opponents and their theory of making baby Universes.
    0 D. Something else.
38. How should the movie end?
    A. As the science says: the people outside the black hole never know whether a baby Universe was made, or what might be the nature of that baby Universe.
    B. The baby Universe should expand out into the old Universe, destroying it, and starting afresh.
    C. Somehow there is an unexpected line of communication from inside the black hole to outside, that allows people outside the black hole to discover what happened.
    D. Postpone the conclusion to a sequel.
    E. Something else.

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Updated 2022 Apr 28