Quiz #2 (07/18/96)

1. The Cosmic Microwave Background Radiation (CMBR) has a characteristic temperature of about 2.7 K, which means that most of it is emitted in the microwave region of the electromagnetic spectrum. Has this temperature always been the same? If your answer is "no", explain why and how it has changed from the time of emission.

2. It would be extremely interesting to observe directly what happened in the first few minutes after the Big Bang. Why is this (even in principle) not possible?

3. 1. If it is not possible to directly observe the first few minutes of the Universe, why do we think we know what happened during this time?
   2. What role do the observed primordial abundances of H² (deuterium) and He⁴ play in this context?

4. Until a few years ago, no fluctuations of the temperature of the CMBR had been detected - the radiation appeared to be perfectly isotropic. Why was this observation very troublesome for astronomers who tried to explain the formation and evolution of structure in the Universe?

5. Even after the necessary fluctuations of the temperature of the CMBR have been detected by improved observations in recent years, astronomers still must include dark matter in their calculations to be able to reproduce the structure we observe in the Universe today.
   1. How does dark matter accelerate structure formation?
   2. Is dark matter a purely theoretical idea, or do we have any observational evidence for its existence?
   3. What might dark matter consist of (give 2 examples).

6. Instead of assuming that dark matter consists of some type of exotic particles that have never been observed, many astronomers would prefer to assume that dark matter is normal (baryonic) matter (consisting of protons, neutrons, and electrons). This matter would be locked up in objects that emit very little light (such as planets or low-luminosity galaxies) and can therefore not be observed directly. According to our standard theory of primordial nucleosynthesis, why must this be wrong?

7. 1. What is the so-called "Horizon Problem" in cosmology and how does inflationary theory solve it?
   2. What is the so-called "Flatness Problem" in cosmology and how does inflationary theory solve it?

8. Stars greater than a solar mass have more fuel to burn than stars like the Sun. Explain qualitatively why they nevertheless do not live as long.

9. Where were most of the atoms of these elements created?
   1. hydrogen (mass=1)
   2. helium (mass=4)
   3. carbon (mass=12)
   4. oxygen (mass=16)
   5. iron (mass=56)
   6. iridium (mass=192)

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