Science Lesson: How Old Is the Universe?

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The universe's exact age is unknown; researchers estimate that the universe is around 13.8 billion years old. Astronomers have two methods of determining the universe's age, according to the National Aeronautics and Space Administration (NASA).

Astronomers can guess the age of the universe using two methods, which are looking for the oldest stars and objects in the universe, and by calculating the rate of the universe's expansion in accordance with the Big Bang theory, which asserts that the universe began with a large explosion called the Big Bang.

Aging Stars
When looking at stars for clues to the universe's beginning, astronomers focus on globular clusters, which are believed to the earliest stars in the universe. Globular clusters are condensed pockets of stars, with approximately one million stars per cluster. Globular clusters formed at approximately the same time, which makes them a reliable source of aging other objects in the universe and figuring out the age of the universe itself. To figure out the universe's birthday using this method, astronomers must first understand the life cycle of a star. They can tell a star's age based on its mass, which also affects its appearance. Stars with a higher mass are brighter than stars with a lower mass. They also burn through their fuel supply more quickly than stars with a lower mass, which means that they have shorter lifespans. Stars with a higher mass that are two times as massive as the sun, for example, burn through their fuel in a time period of about 800 million years, while it takes a star with a mass that is 10 times the mass of the sun only about 20 million years to exhaust its fuel supply. Astronomers can determine the age of an entire globular cluster once they find the age of one star in that cluster.

Hubble Constant
The other method that astronomers use to determine the age of the universe is by measuring its rate of expansion, which is called the "Hubble constant," abbreviated as H0. The H0 is a measurement used to find the current expansion rate of the universe. Using this measurement, astronomers can compare the expansion rate to the Big Bang, which experts believe indicates the birth of the universe. There are several variable factors in this method of calculation, including the density and composition of the universe. Scientists must determine the amount of regular matter and energy compared to dark matter and energy, which helps them understand the universe's composition. Objects that have a lower density are older than objects with a higher density.

Tools and Technology
Astronomers have several ways to determine factors like density and composition of the universe. In time, their findings have become more accurate and reliable with the advent of technology, including computers and modeling tools. Sending spacecraft on missions to collect data also helps scientists gather data about the universe. A mission launched by the NASA, called the Wilkinson Microwave Anisotropy Probe, and the European Space Agency's Planck spacecraft, have been able to measure thermal radiation left over from the Big Bang, which has helped astronomers get a better understanding of the universe's age. As technology continues to improve, scientists hope to get even more accurate information down the road that tells them more precisely how old the universe is.