How Old Is The Universe?

The universe is both vast and ancient. You may have heard that the universe is about 14 billion years old, yet how exactly is this determined? Knowing the age of the universe may seem like it’s something beyond human capability, yet there are fairly simple ways of determining how old our universe is. However, it is important to note that the age of the universe is still somewhat of a mystery, and future observations will likely reveal more information. There are two primary methods for determining the age of the universe: the oldest stars and the rate of the universe’s expansion

The Oldest Stars

History of the universe
   Illustration of the history of the universe, from the Big Bang till now. 

By knowing the age of the oldest stars, astronomers can estimate how old the universe must be. The oldest known star in the universe is called Methuselah, named after the oldest individual in the bible. Even prior to calculating its age, astronomers knew Methuselah was old based on its composition. Since most elements heavier than hydrogen and helium form within stars, the first stars would have had little to no elements heavier than helium. Methuselah itself is composed almost entirely of hydrogen and helium, with no evidence of many elements heavier than helium. Thus, Methuselah must have formed when the universe contained nothing but hydrogen and helium. This would make Methuselah one of the oldest stars in the universe, yet when astronomers calculated its age, problems arose. Based on observations of other stars and the expansion of space, the best estimates for the age of the universe were around 13.8 billion years old, yet the age of Methuselah was calculated to be 16 billion years old. Obviously a star cannot be older than the universe, so either the age of the universe is wrong or the age of Methuselah is wrong. Future observations have only added to this problem, with most estimates of Methuselah’s age placing it older than the universe or the same age as the universe. Based on observations of the early universe and other stars, it seems like the age of Methusalah is probably wrong, and although the star is among the oldest stars, it likely formed around 13 billion years ago. Observations of other old stars have been consistent with a universe that is between 13 and 14 billion years old. 

Expansion Of Space

CMBR
The Cosmic Microwave Background is the oldest image of the universe. Here, we see the cosmos as it was a mere 380,000 years after the Big Bang, nearly 13.8 billion years ago. 

The expansion of space is perhaps the most reliable method at determining the age of the universe. In fact, the expansion of space was the first hint that the Big Bang actually happened. If the universe is constantly expanding, it means that the universe of the past was smaller than it is today. If you work backwards, you end up at a point where everything in space was condensed into a single point no larger than an electron. By knowing how fast space is expanding, all you need to do is put things in reverse and see how much time has passed since everything was a single point. By using this method, scientists estimate that the universe began in the Big Bang about 13.8 billion years ago. However, as is the case with much of science, future observations and data may reveal more detail about the age of the universe, revealing that the universe could potentially be older or younger than what we currently think. 

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