World Science Scholars
3.2 Inflation
summary
Inflation is the most popular theory about the evolution of the early universe.

• The theory requires one assumption to be made: There existed a tiny region of exotic material—a fraction of the size of a proton—that was extremely hard to dilute.
• Expanding its volume resulted in its density staying almost the same.
• This tiny region doubled in size rapidly for some time, eventually becoming about the size of a marble.
• At this time, the marble-sized region slowed, cooled, and coasted while still increasing in size, ultimately encompassing the observable universe.

Inflation can account for many previously unsolved mysteries.

• The theory of inflation presents an explanation for what caused our Big Bang.
• Inflation solves the Horizon problem—in the conventional Big Bang model, a mechanism to establish uniformity would require information to travel at 100 times the speed of light. Inflation solves this by assuming the incredibly small early universe could easily establish uniformity; then, inflation stretches the region while maintaining the uniformity.
• Inflation predicts the flatness of the universe, related to the relative mass density Ω:$$\Omega = \frac{\text{Actual mass density}}{\text{Critical mass density}}$$ where the critical density depends on the expansion rate of the universe.
 $$\Omega = 1$$ $$\longrightarrow$$ Flat $$\Omega > 1$$ $$\longrightarrow$$ Closed $$\Omega < 1$$ $$\longrightarrow$$ Open
• If the universe were curved even slightly, it would have significant effects on the nature and ultimate fate of the universe. Inflation solves the mystery of how Ω is so closely “fine-tuned” to 1 (the flatness problem) because Ω is driven rapidly toward 1 in the inflationary picture.
• Quantum fluctuations in the early universe created the structure and clustering we see today, according to another prediction of the theory of inflation.
• Finally, inflation predicts gravitational waves—considered the “holy grail” and “smoking gun” of inflation. The BICEP2 team may have recently discovered the existence of primordial gravitational waves.

Recent discoveries have helped to eliminate many issues with the inflationary model.

Requirements for Inflation Recent Discovery/Solution
A substance that isn’t diluted by expansion $$\longrightarrow$$ Dark energy, discovered 1998
The existence of a scalar field $$\longrightarrow$$ Higgs field, discovered 2013
Testable Predictions $$\longrightarrow$$ Potential energy function:predictions agree strongly with measured observations

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