Summary
Highlights
The universe is expanding, and we know this due to evidence from redshift. This video will explore Edwin Hubble's use of the Doppler effect to support the expanding universe theory.
Before Edwin Hubble, the universe was thought to be static. Hubble studied light from galaxies, noting that elements in a star's atmosphere absorb specific wavelengths of light. These absorptions create Fraunhofer lines in a star's light spectrum, revealing its chemical makeup and distance.
The Doppler effect is a change in wavelength and pitch for sound, or wavelength and color for light, when the source is moving relative to an observer. An example is the changing sound of a police siren as it passes. The same principle applies to light from distant stars.
When a star moves away, its light shifts to a lower frequency, moving towards the red end of the spectrum, known as redshift. Hubble observed that most galaxy light was redshifted, and the further away a galaxy was, the more pronounced its redshift. This led to his conclusion that galaxies are moving away from us, and the universe is expanding.
Comparing the sun's spectrum to a distant star's shows a shift of the absorption lines towards the red end for the distant star. This confirms their movement away from us. Redshift also supports the Big Bang theory.