Expansion of the universe was first observed and measured by which scientist?

• A. Isaac Newton
• B. Carl Sagan
• C. Edwin Hubble
• D. Galileo Galilei

Answer: (C)

Expansion of the universe is shown by galaxies moving away from us, with their speeds increasing the farther they are. Edwin Hubble pulled this together in 1929 by measuring how far other galaxies are and comparing those distances to how fast they’re receding (from their redshifts). He used Cepheid variables to gauge distances and then paired that with spectral redshifts, revealing a clear, proportional relationship between distance and recessional speed—now called Hubble’s law. That combination of direct distance measurements with redshift data made the expansion a measurable, testable reality.

Other figures didn’t make this discovery in the same way. Newton laid the groundwork for gravity but not the observation of cosmic expansion, Galileo contributed early telescope observations, and Carl Sagan was a popularizer rather than the one who measured this effect.