How do astronomers estimate the size of the universe?

Since we can only see the portion of the universe that is close enough to us that light from it has had time to arrive here, no one can determine the exact size of the universe. That means that any part of the universe that would require more than 14.5 billion years for light to travel to us cannot be seen. Alternatively, it is possible that the universe is infinite in size.

The sphere that surrounds us and is known as the "visible universe" has a radius of roughly 50 billion light years. This is greater than the universe's age of 14.5 billion years because the universe is expanding faster than the speed of light.

The term "red shift" refers to the method used by scientists to measure the size of the visible universe. Just as a car horn's pitch changes as it passes you because of doppler shift, light also shifts in frequency or color depending on whether it is traveling toward or away from you. The more quickly an object moves away from you, the more red shift it experiences. This allows us to estimate the distance an object is from us; the furthest objects we can see are approximately 50 million light years away.

Astronomers estimate the size of the universe using methods such as triangulation, redshift measurements, and observations of cosmic microwave background radiation.