How did scientists determine the speed of the expansion of the universe?

Upon observing other galaxies in the universe, we find that most of them are moving away from us. These galaxies undergo redshift, or the change in wavelength from our perspective, which makes their light appear redder than that of galaxies moving toward us. This information is used to calculate the expansion's speed.

The lengthening of light waves as objects emitting them move away is a phenomenon known as redshift, and scientists have used this to measure the speed of the universe's expansion by observing the light from distant galaxies. The more redshift a galaxy has, the faster it is moving away from us, indicating the universe's expansion.

Scientists determined the speed of the expansion of the universe primarily through observations of distant galaxies. They used various techniques, including measuring the redshift of light from these galaxies and observing the cosmic microwave background radiation. The redshift of light from galaxies indicates their recessional velocity, which is a result of the universe's expansion. By analyzing the redshift of galaxies at different distances, scientists were able to infer the rate of expansion, known as the Hubble constant. Additionally, measurements of the cosmic microwave background radiation provide further evidence for the expansion of the universe and help refine our understanding of its speed over cosmic history.