Which theory explains the expansion of the universe from a dense initial state?

• A. Steady State Theory
• B. Big Bang Theory
• C. Heliocentric Model
• D. Plate Tectonics

Answer: (B)

The idea being tested is how scientists explain the universe expanding from a hot, dense beginning. The Big Bang Theory says the universe started from an extremely dense and energetic state and has been expanding over billions of years. This fits a wide range of evidence: distant galaxies are redshifted, meaning they are moving away and faster as they’re farther away (Hubble’s observations); there is a faint afterglow everywhere called the cosmic microwave background, leftover radiation from the early hot phase; and the amounts of light elements like hydrogen and helium observed in the cosmos match predictions from early rapid nucleosynthesis. Together, these clues point to a history of expansion starting from a dense origin.

The other ideas don’t align with this broad set of observations. The Steady State view suggests matter is continuously created to keep density constant as the universe expands, but it doesn’t explain the cosmic microwave background or the specific elemental abundances. The Heliocentric Model describes the Sun’s position in our solar system, not the expansion of the universe. Plate Tectonics explains movements of Earth’s crust, not cosmic-scale evolution.