Hubble’s Law of Cosmic Expansion

22.03.2015 |

Episode #3 of the course “Scientific laws and theories everyone should know”

While the 1920s rushed on and the Great Depression darkened society, Edwin Hubble was conducting cutting-edge research on astronomy. In 1929, Hubble demonstrated that other galaxies besides the Milky Way existed and that those galaxies were moving away from us in a process he termed “recession.” Thus, Hubble’s law essentially provides a rate at which the universe is expanding.

In order to numerically represent the momentum of the movement of galaxies, Hubble proposed Hubble’s Law of Cosmic Expansion (Hubble’s Law), which reads: velocity = H0 × distance. Velocity demonstrates recessional rate of movement for the galaxy while H0 is the Hubble constant. H0 is the guideline that tells the estimated rate of how fast the universe is expanding and this distance pertains to the distance between the two galaxies that are being compared. It is often referred to as the Hubble constant, but it is not really a constant at all.

Hubble’s constant has been measured and valued differently over the years, but currently the standard value is 70 kilometers/second per megaparsec. Megaparsec represents a unit of measure for the distance in the cosmos. Hubble’s law gives us a succinct and exact way to measure velocity of related galaxies. Further, the law demonstrated that the universe contains many galaxies, all of which can trace their movements back to the Big Bang. Clearly, this theory has been very useful in science overall.

Hubble’s Law served as the first real evidence of Einstein’s theory of General Relativity as applied and tested to the whole universe. The wholly applicable nature of General Relativity is the central guidepost of the Big Bang theory. The way we observe spatial expansion is at the speed that things appear to move away from our galaxy in proportion to their distance, which is Hubble’s Law.


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