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1. **Doppler Effect**: Redshift occurs due to the Doppler effect, where light from moving objects changes frequency. Objects moving away from us show longer (redder) wavelengths.
2. **Observed Redshift**: Astronomers observe that most distant galaxies exhibit redshift, indicating they are moving away from Earth.
3. **Hubble's Law**: Edwin Hubble discovered a correlation between a galaxy's distance and its redshift—more distant galaxies have higher redshifts, supporting expansion.
4. **Expanding Universe Model**: The redshift data suggests that space itself is expanding, causing galaxies to recede from each other over time.
5. **Big Bang Theory**: The concept of redshift aligns with the Big Bang theory, indicating that the universe has been expanding since its inception.