Math in the Physical Sciences

Astronomy and Math

What is the Hubble constant?

Astronomers have always been interested in the age of our universe and the speed of various objects in space. The Hubble constant was devised by American astronomer Edwin Hubble (1889–1953). It is the ratio of the recessional speed of a galaxy—because the universe is expanding—to its distance from the observer. In other words, the velocity at which a typical galaxy is receding from Earth, divided by its distance from Earth.

The reciprocal of the Hubble constant is then thought to be the age of the universe, usually written in terms of kilometers per second per million light years. If the number is high, the universe would be very young; if the number is low, the universe would be much more ancient. Although there have been numerous theories, the true age of the universe is usually considered to be somewhere between 12 and 20 billion years old.

The most recent agreed-upon rate at which the universe is expanding is approximately 20 kilometers per second per 106 light years of distance. That makes the universe about 15 billion years old.


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