- In version 1, how many neutrons are left at 50 seconds or later?
- The Universe is too hot to make helium before 150 seconds. In version 1, how much helium was made in the Big Bang (remember that helium is made of two protons and two neutrons)?
- Look at the equilibrium reaction speed column in Table 1.
Why might the equilibrium neutron fraction be incorrect at 50 seconds?
- Circle groups of two neutrons and two protons (helium nuclei).
- What fraction of helium did you get by
**number**? ie. What is:# helium/(# helium + # deuterium + # protons)

- Assume each proton and neutron weigh the same. What fraction of
**the mass**is now in helium? What fraction of the mass is in deuterium? - What fraction of helium did you get by
**number**? i.e. what is: #helium/(#helium+#deuterium+#protons) - What fraction of
**the mass**is now in helium? What fraction of the mass is in deuterium? - Did you get more or less helium when deuterium formed earlier?
- Version 3 of the Early universe is a fairly accurate reflection
of the models astronomers actually use. Is your mass fraction in the usual
range of 20-30 percent that theoreticians predict?
- Deuterium forms sooner when there is more matter in the universe.
Suppose that the most accurate theoretical calculations predict that for a
helium fraction of 25%, the density of ordinary matter (stars, gas, people
etc...) is 2 x 10
^{-31}grams per cubic centimeter. If observers measured a definitive helium fraction of 30 percent what would you predict about the actual density of ordinary matter compared to this value?