Estimating the Universe’s Age with Redshift and Oldest Stars

The age of the universe is estimated to be 13.7 billion years, a figure that aligns with NASA’s estimate of roughly 13 billion winters. Scientists arrive at this number using two primary methods: one based on the redshift of distant light and another based on dating the oldest known celestial bodies.

Method 1: Redshift and Expansion Calculation

When astronomers observe starlight from distant galaxies, they see the light shifting toward the red end of the spectrum. Chemical elements emit specific colors when they gain or lose energy, but hydrogen and helium—the main constituents of stars—cannot produce the particular shades of red observed from far‑away objects. The shift therefore results from the motion of the light source.

Redshift occurs when a light source moves away from an observer, stretching the wavelength and moving the color toward red. Conversely, blueshift happens when the source moves closer, shrinking the wavelength and shifting the color toward blue. Most, if not all, far‑off stars and galaxies display redshift, indicating they are receding from us.

If these objects are moving away now, they must have been much closer together in the past. Tracking their paths suggests that everything in space originated from a single point, a singularity. This concept underlies the Big Bang theory, which posits that the universe began with an explosive event and has been expanding ever since.

Scientists measure the speed and velocity of receding galaxies, calculate the rate of expansion, and insert those values into a mathematical equation. The result of that calculation yields an age of about 13.7 billion years for the universe. As one quoted line puts it, “The red color indicates that the stars are constantly and quickly traveling away from us.”

Method 2: Age of Oldest Celestial Bodies

People have studied stars for centuries, learning the stages of their life cycles. By estimating how long the oldest stars have existed, researchers can set a lower bound on the universe’s age: the cosmos must be at least as old as its oldest constituents.

The oldest star identified so far is estimated to be 13.2 billion years old. Many other ancient stars have ages close to 12 billion years, while none have been found near 14 billion years. This pattern supports the calculations derived from redshift data. As the speaker notes, “The idea was as follows: If we find a star that is (X) years old, we now that the universe is at least older than (X).”

Although the age of a single star cannot definitively fix the universe’s age—future discoveries could shift the estimate—the agreement between this method and the redshift approach gives scientists confidence in the 13.7 billion‑year figure.

Conclusion and Recap

The universe’s age is therefore placed at 13.7 billion years. The discovery process can be summarized in three steps: first, astronomers observed that distant stars are moving away; second, they calculated the time required for those stars to reach their current positions using the expansion rate; third, they dated the oldest stars. The convergence of these independent lines of evidence confirms the estimated age of the cosmos.