I recently gave a talk at the Faith and Astronomy Workshop in Tucson, Arizona. It was wonderful to have this opportunity and to see familiar faces and to meet the new attendees as well. The talk was on the building blocks of the Milky Way.
The term “Lego” is used in particular as we now know that the Milky Way is built up from many small ‘blocks’ of material. We also have tool to see what these Legos looked like. This is because we also know that the speed of light is finite, so that when we look back in space we are necessarily also looking back in time.
Interestingly, this means that as we look out into the distant universe we are seeing objects as they looked a long time ago. If we look at a galaxy whose light took 10 billion years to reach us then we are seeing what this galaxy looked like 10 billion years ago. We have no way to know what is looks like today.
Similarly, if there are intelligent beings on a planet orbiting a star in a galaxy 10 billion light years away then they will only ever be able to observe the Milky Way as it looked 10 billion years ago. How interesting that would be! What did the Milky Way look like so long ago?
With deep Hubble Space Telescope imaging we are able to see distant, faint galaxies whose light is indeed 10 billion years old. Since we say that the universe is homogeneous and the same in all directions (isotropic), pictures of such distant objects should look rather like the Milky Way did in its youth.
When we do this, we find the Milky Way does not look like a tiny spiral galaxy, nor does it look like the giant spiral galaxy that it is today, but rather it looks like it is made of tiny fragments of stars and star forming material. We now think that these galaxy fragments, or Legos, are what was built up over billions of years to achieve the spectacular spiral galaxy in which we reside.