Our Evolving Universe
Self Test 11

1. Helium is formed in the early universe, but carbon is not, because
   1. the early universe is too hot to form carbon
   2. the early universe is too cool to form carbon
   3. the process is blocked by the lack of stable nuclei with atomic mass 5 or 8
   4. the neutron lifetime is not long enough for carbon to form
   
   
2. The cosmic microwave background was emitted
   1. when matter and antimatter annihilated, a fraction of a second after the Big Bang
   2. when helium was formed, about 3 minutes after the Big Bang
   3. when electrons combined with nuclei to make neutral atoms, about 300,000 years after the Big Bang
   4. when the first stars started to fuse hydrogen to helium, several million years after the Big Bang
   
   
3. There are now about a billion times more photons than protons because
   1. almost all of the original matter annihilated with antimatter
   2. the photons carry much less energy than the protons
   3. the universe is radiation dominated
   4. the universe is expanding
   
   
4. The extreme smoothness (isotropy) of the cosmic microwave background
   1. is expected, because the universe started with a Big Bang
   2. is surprising, because the universe started with a Big Bang
   3. is expected, because the universe was smaller when the microwave background radiation was first emitted
   4. is surprising, because light did not have time to travel across the now-visible universe before the background radiation was emitted
   
   
5. The inflation theory
   1. explains why the cosmic microwave background is very isotropic
   2. predicts that the universe should be flat (zero curvature)
   3. involves a very short period of very rapid expansion a tiny fraction of a second after the Big Bang
   4. all of the above

out of 5.

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