So, on the 10^n scale, today Space.com posed the interesting question “What Is the Biggest Thing in the Universe?”
Scientists have created the first map of a colossal supercluster of galaxies known as Laniakea, the home of Earth’s Milky Way galaxy and many other. This computer simulation, a still from a Nature journal video, depicts the giant supercluster, with the Milky Way’s location shown as a red dot.
What’s bigger than a galaxy? Well, groups or clusters of galaxies and then superclusters.
[Wiki] A supercluster is a large group of smaller galaxy clusters or galaxy groups, which is among the largest-known structures of the cosmos. The Milky Way is part of the Local Group galaxy cluster (that contains more than 54 galaxies), which in turn is part of the Laniakea Supercluster. This supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years. The number of superclusters in the observable universe is estimated to be 10 million.
On the scale of space and time, the Space.com article notes:
The biggest supercluster known in the universe is the Hercules-Corona Borealis Great Wall. It was first reported in 2013 and has been studied several times. It’s so big that light takes about 10 billion years to move across the structure. For perspective, the universe is only 13.8 billion years old.
But what really struck my interest was a point about the existence of such structures and cosmology’s guiding principle of universal homogeneity — the cosmological principle.
A 2013 article from Discovery News (a partner site to Space.com) pointed out that this structure appeared to go against a principle of cosmology, or how the universe formed and evolved. Specifically, this principle says that matter should be uniform when seen at a large enough scale. The cluster, however, is not uniform.
That caveat about the cosmological principle — “when viewed on a large enough scale” — has always seemed fuzzy to me. It boggles the mind when galaxies are viewed as pixels on a cosmic map, eh.