If you have ever dreamed of time travel, just look at the night sky. The shimmer you see is a snapshot of the distant past. That’s because these stars, planets and galaxies are so far away that the light itself can take tens of thousands of years to reach Earth. The universe is undoubtedly a big place.

But how big is it? Maybe we do not know that, “said Sarah Gallagher, astrophysicist at Western University in Ontario, Canada, opposite Live Science. The size of the universe is one of the fundamental questions of astrophysics. It could also be impossible to answer. But that does not stop the scientists from trying. The closer an object is to the universe, the easier it is to measure its distance, Gallagher said. The sun? Piece of cake. The moon? Even easier.

All scientists have to do is direct a ray of light upwards and measure the time it takes for this ray to bounce off the lunar surface and return to Earth. But the farthest objects in our galaxy are more difficult, Gallagher said. After all, it would take a very strong beam of light to reach it. And even if we had the technological ability to shine a light so far, then who has millennia to wait for the beam to bounce off the distant exoplanets of the universe and return to us?

Scientists have some tricks to deal with the farthest objects in the universe. Stars change color as they age.Using this color, scientists can estimate how much energy and light these stars emit. Two stars with the same energy and brightness will not appear the same from Earth if one of those stars is much further away. The farther you go, the darker it seems, of course. Scientists can compare the actual brightness of a star with what we see from Earth, and use that difference to calculate how far away the star is, Gallagher said.

But what about the absolute edge of the universe? How do scientists calculate distances to distant objects? Here it is really tricky. Remember, the farther an object is from Earth, the longer it takes the light from that object to reach us. Imagine that some of these objects are so far away that their light took millions or even billions of years to reach us.

Now imagine that the light of some object takes so long to make this journey that it has not reached the earth in all the billions of years of the universe. That’s exactly the problem that astronomers face, said Will Kinney, a physicist at New York’s State University in Buffalo, to Live Science. We can only see a little bubble [of the universe]. And what is outside of it? We do not really know, “Kinney said. However, by calculating the size of this small bubble, scientists can estimate what is outside the bladder.

Scientists know that the universe is 13.8 billion years old, give or take a few hundred million years. This means that an object whose light took 13.8 billion years to reach us should be the farthest object we can see. You may be tempted to believe that this gives a simple answer to the size of the universe: 13.8 billion light-years. Remember, however, that the universe is also expanding at an ever-increasing rate.

In the time it took the light to reach us, the edge of the bubble moved. Fortunately, the scientists know how far it has progressed: 46.5 billion light-years away, based on calculations of the expansion of the universe since the Big Bang.

Some scientists have used this number to calculate what is beyond the limit of what we can see. Based on the assumption that the universe has a curved shape, astronomers can look at the patterns that we see in the observable universe and use models to estimate how far the rest of the universe expands. One study found that the actual universe could be at least 250 times larger than the 46.5 billion light-years that we can actually see. But Kinney has other ideas: “There is no evidence that the universe is finite,” he said.”It could go very well forever.”

There is no sure saying that the universe is finite or infinite, but scientists agree that it is “really damn big,” Gallagher said. Unfortunately, the small part we can now see is the biggest we can ever see. As the universe expands at an accelerating rate, the outer edges of our observable universe actually move outward faster than the speed of light. This means that the edges of our universe move away from us faster than their light can reach us.

Gradually, these edges disappear (and all the restaurants there, as the British author Douglas Adams once wrote) out of sight. The size of the universe and the amount we can not see – that’s humiliating, said Gallagher.

But that does not stop them and other scientists from continuing to seek answers. Maybe we can not figure it out. It could be considered frustrating, “said Gallagher. But it also makes it really exciting too.