Briefly describe one of the three quandaries that are solved by inflation; that is, describe either the structure problem, the smoothness problem, or the flatness problem

Question

What will be an ideal response?

Answer 1

Structure problem: The fact that there are galaxies means that the density of the early universe differed slightly from place to place. The temperature differences in the cosmic background radiation show that regions of enhanced density did exist at the end of the era of nuclei, when the universe was 300,000 years old. However, the standard Big Bang theory cannot explain where these density enhancements originally came from.

Smoothness problem: Observations of the cosmic background radiation show that the density of the universe at the end of the era of nuclei varied from place to place by no more than about 0.01 percent. This means that two regions of the universe that have not had time to be in contact with each other yet are almost at exactly the same temperature. The coincidence that almost the entire universe would be in equilibrium without having contact among various regions is almost impossible.

Flatness problem: The density of the matter in the universe is around 20-100 percent of the critical density. Since the Big Bang theory does not state anything about what the density of the universe should be, why would it be so close to this density? Another way to state this problem is to say that the universe is very flat. If the universe had been 10 percent denser at the end of the era of nuclei, it would have recollapsed long ago. If it had been 10 percent less dense at this time, galaxies would never have formed before expansion spread the matter too thin.