What evidence supports the Expanding Universe Theory?

• A. Observations of the movement of distant galaxies
• B. The presence of dark matter
• C. Moon's orbit
• D. Solar eclipses

Answer: (A)

The main idea here is evidence for the universe expanding. Distant galaxies don’t just move around randomly; their light shows a telltale redshift—the spectra shift toward longer wavelengths. That redshift increases with distance, so farther galaxies appear to be moving away faster. This pattern, known as Hubble’s law, points to the fabric of space itself stretching over time, causing galaxies to recede from us and from each other. That expanding-space picture is the strongest observational support for the Expanding Universe Theory.

The other topics don’t directly demonstrate cosmic expansion. Dark matter explains why some systems rotate or lens more than visible matter accounts for, but it doesn’t reveal the large-scale expansion of the universe. The Moon’s orbit and solar eclipses are governed by gravity within the Earth–Moon–Sun system and reflect local celestial mechanics, not the expansion of space on cosmological scales.