AstronomyLesson 1 of 1 in the course The Big Bang

Inflation and the Early Universe: Puzzles, Forces, and Evidence

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

The hot Big Bang model successfully explains the expansion of the universe, the cosmic microwave background (CMB), and the abundance of light elements. Yet it leaves important questions about the universe as a whole unanswered. This lesson introduces two major puzzles: why the universe has critical density and why the CMB has nearly the same temperature in every direction.

All flashcards

Critical density
The density associated with spatial flatness in the simplified cosmological model; substantial departures are associated with curvature.
Horizon distance
The maximum distance over which information could have traveled to or from a region during a specified period.
Horizon problem
The puzzle of how regions unable to communicate came to have nearly the same CMB temperature.
Cosmic inflation
A hypothesis that the early universe underwent a brief period of extraordinarily rapid expansion.
Grand unified theory (GUT)
A proposal that the strong, weak, and electromagnetic forces were unified under early-universe conditions.

Quiz questions

  1. Which forces do grand unified theories, as described here, propose were once unified?Answer: The strong, weak, and electromagnetic forces
  2. Compared with the other fundamental forces, how strong is gravity between elementary particles?Answer: It is by far the weakest.
  3. What role does the strong nuclear force play in ordinary atomic nuclei?Answer: It holds protons and neutrons together.
  4. The Planck time refers to the interval from the beginning of the universe to approximately what time?Answer: 10⁻⁴³ second
  5. Which possible observation is discussed as an indirect test of inflation?Answer: A gravitational-wave imprint in the cosmic microwave background

Based on Astronomy 2e by Andrew Fraknoi, David Morrison, Sidney Wolff (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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