Review

#06

The idea is that the fusion of H to He could occur in the early universe. The abundance would be the same everywhere, and then stars would eventually form out of this material, so all stars have similar He abundances.

#07

It takes higher and higher temperatures to form heavier elements beyond He, but the temperature in the universe decreases as it expands.

#13

Inflation is a period that may have caused the universe to expand much more rapidly at it beginning moments than we see it expand today.

#14

Inflation permits the possibility that distant parts of the universe were in much closer contact in the early universe. This would account for how the microwave background at opposite sides of the universe can have such similar temperatures.

#15

There is no reason why the universe should be so flat. It could have any kind of curvature. Supposing it originally had some wildly non-flat curvature originally, inflation would stretch out space by such incredibly large factors, that the curvature would appear flat for the extent of the universe that we can observe.