The universe is incredibly vast, but the question remains: just how vast is it? In fact, the size of the universe has always been one of the fundamental questions of astrophysics.
“This is probably an issue we will never know the answer to,” says astrophysicist Sarah Gallagher of Western University in Ontario, Canada. However, this doesn’t deter scientists from attempting to answer this question.
Gallagher explains that objects closer to us are easier to measure. For instance, scientists can simply send a beam of light toward Earth’s natural satellite, measure the time it takes for the light to touch the surface of the Moon and bounce back to Earth. However, a similar approach cannot be applied when measuring distant objects within the Milky Way. Even if humanity possessed the technology to launch an extremely powerful light beam, no one could sit around for thousands of years waiting for that beam to return.
Scientists have devised some clever tricks to try to measure the most distant objects in the universe. Stars change colors over time, and based on this phenomenon, scientists can estimate the amount of energy and light they emit.
Two stars with similar energy and brightness will appear differently in Earth’s lens if one of them is farther away. Distant stars will naturally appear fainter. Therefore, scientists can compare the actual brightness of a star with what we observe from Earth and use this difference to calculate how far away it is, according to expert Gallagher.
Measuring the edge of the universe poses a different challenge. It’s essential to remember that the farther an object is from Earth, the longer it takes for light to reach our planet. Consider the scenario where light emitted from objects takes billions of years to reach our planet. This is a predicament that astrophysics has to grapple with.
“We can only see a tiny, sphere-shaped part of the universe,” says physicist Will Kinney of the State University of New York. Nevertheless, by calculating the size of this tiny sphere, scientists believe they can estimate the rest of the universe.
The universe is currently estimated to be about 13.8 billion years old, with a margin of error of several hundred million years. Additionally, the universe is continually expanding at an accelerating rate. By the time light from the universe’s edge reaches Earth, that edge has moved. Fortunately, scientists have determined that the edge of the universe has moved 46.5 billion light-years away.
In other words, even though it takes approximately 13.8 billion years for light to travel across the universe, the distance from the universe’s edge to Earth’s current position is 46.5 billion years.