1. Redshift:
* Doppler Effect: We know that the sound of a siren changes pitch as it approaches and moves away from us. This is the Doppler effect, and it applies to light as well. When an object moves towards us, the light waves get compressed, shifting towards the blue end of the spectrum (blueshift). When an object moves away from us, the light waves stretch out, shifting towards the red end of the spectrum (redshift).
* Spectral Lines: Every element emits and absorbs light at specific wavelengths, creating unique spectral lines. Astronomers observed that the spectral lines of distant galaxies were shifted towards the red end of the spectrum.
2. Hubble's Law:
* Edwin Hubble in the 1920s meticulously measured the redshift of galaxies and their distances. He found a direct correlation: the farther away a galaxy was, the greater its redshift.
* Hubble's Law stated that the speed at which a galaxy is moving away from us is directly proportional to its distance. This led to the conclusion that the universe is expanding.
3. Implications:
* Expansion: The redshift observations meant that galaxies were not just moving randomly, but were moving apart from each other. This indicated an expanding universe, not a static one.
* Big Bang: The idea of an expanding universe fit well with the theoretical framework of the Big Bang, which suggested that the universe began in a very dense and hot state and has been expanding ever since.
In summary, scientists observed the redshift of light from distant galaxies, which was consistent with the Doppler effect, suggesting that these galaxies were moving away from us. This observation, combined with Hubble's Law, led to the groundbreaking conclusion that the universe is expanding, a key cornerstone of the Big Bang theory.
