Some hundreds of years ago it was thought that the Earth was the centre of the universe, that our planet was stationary, and that all the other bodies we see in the sky orbited around us in different layers. Nowadays, this vision of the universe is known as the geocentric model.
This conception of the universe changed when Nicolaus Copernicus published an article where he demonstrated that the Earth and the other planets orbited around the Sun, consequently creating the heliocentric model. Although Copernicus published this article in 1543, more than a century went by before the heliocentric model was accepted by the scientific community and the Church, due to the revolution and changes that entailed this statement at that time.
Nowadays, our vision of the universe has been radically changed, after having discovered uncountable galaxies formed each of them by hundreds of billions of stars. We have realised that the Earth doesn’t occupy any privileged position in the universe, and it is only a small planet orbiting the Sun in one of the branches of the Milky Way, our galaxy.
The centre of the observable universe
As we have just seen, the Earth doesn’t occupy any special place in the universe. In fact, as it has been studied for many years, and as we will see in a coming post, it is very likely that there is not even a point that is the centre of the universe.
However, it is also true that we find ourselves in the centre of our observable universe. From the Earth, we observe that, in all directions, the universe spreads out as far as 14 billion light years in distance. This is due to that, since the universe was formed, only the light of the objects that are found inside this sphere of 14 billion light years of radius, has been able to reach us.
In other words, the Earth is found in the centre of a sphere (the universe) 14 billion light years in radius. However, this not only happens with the Earth, but with any other body in the universe that is taken as a reference. For example, a planet on the other side of the galaxy will have a different observable universe than we have, because the light of bodies that are found beyond our observable universe will have been able to reach that planet.