A Sense of Scale Page 11

14 billion light years

The known visible Universe extends to 14 billion light years around us. The sheets and walls of Super Clusters give the Universe a cellular appearance.

This diagram is an impression of this entire region. The number of Super Clusters in the visible universe is estimated to 10 million.

 Dilemma In our scale model, 14 billion light years correspond with a distance of 133 billion km or roughly the size of our Solar System, including the Oort Cloud.   Remember that the average star is 1 mm in size in this scale model. So what kind of scale model is that? We make scale models to see the true scale of something in a small area. But if we want to see individual stars as grains of sand, like we do in our model, the scale model itself becomes larger than planet Earth, long before we can see the Milky Way galaxy. If we limit the size of the scale model of the visible Universe (the diagram on this page) to the size of planet Earth, we have to shrink the original model by a factor of ten million. Then we end up with our Sun having a size of 1.3 x 10-7 mm or about the size of a Helium atom. These model "atoms" are then at a typical distance of 5 mm apart within a galaxy. Can we call that a scale model? Well, that depends on what you want to see. But the bottom-line is that we cannot really say that we can comprehend distances and sizes in the Universe. We can look at the numbers and do our calculations, but we have no way of relating these to our every day experience. We can conclude however that the Universe is very empty because there is such a large distance between neighbouring stars as compared to their size, and even more so between galaxies, clusters and super clusters. The Universe is a very empty place.

Image: Atlas of the Universe

Jan Vermeer - The Astronomer
(c. 1668, Oil on canvas, 50 x 45 cm)