ESS Regents Practice Exam

The main idea being tested is what lines of evidence most strongly support the Big Bang model. The strongest trio of clues are the observed red shift of galaxies, the cosmic microwave background, and the primordial abundances of light elements.

Red shift shows that galaxies are moving away from us, and more distant galaxies are receding faster. This implies that space itself is expanding, pointing to a single hot, dense origin for the universe rather than a static cosmos.

The cosmic microwave background is the faint, uniform glow left over from the early, hot era of the universe when photons decoupled from matter. Its existence and nearly uniform temperature across the sky match precise predictions of a universe that started hot and has been expanding and cooling over time.

The observed abundances of light elements—mostly hydrogen and helium with trace amounts of lithium—align with what Big Bang nucleosynthesis predicts for the amounts produced in the first minutes after the initial expansion. This quantitative agreement across multiple elements provides a strong test of the model’s early conditions.

Other options don’t fit as evidence for the Big Bang. Flat rotation curves of galaxies point to dark matter distribution within galaxies rather than to the origin of the universe. The existence of black holes concerns extreme gravity and stellar evolution, not initial cosmic expansion. The absence of distant supernovae isn’t a recognized line of evidence for the Big Bang; in fact, observations of distant supernovae have played key roles in understanding the universe’s expansion history, including the discovery of late-time acceleration.