Which is good, because if they do, they violate the cosmological principle.
In theory, the Universe should be the same, on average, everywhere.
On the largest scales, it shouldn’t matter which direction you observe.
Nor should it matter which location you’re examining.
We expect isotropy and homogeneity, with physical consequences if they’re violated.
Initially, the Big Bang simultaneously occurred everywhere.
All locations possessed equivalent temperatures and densities.
Only tiny, 1-part-in-30,000 imperfections get superimposed atop them.
Those imperfections then evolved gravitationally, limited by our physical laws.
Tremendous cosmological structures formed: stars, galaxies, and the great cosmic web.
We expect a structural size limit: ~1.2 billion light-years.
Anything larger wouldn’t have sufficient time to form.
We’ve discovered many enormous galaxy “walls” in space.
Similarly, great cosmic voids exist between them.
These largest structures approach, but don’t significantly exceed, the expected cosmic limits.
But two classes of structures threaten this picture.
Three separate large quasar groupings are clustered across too-large cosmic scales.
Similarly galaxy groups from gamma-ray burst mapping surpass these limits.
If real, these structures defy our present cosmic understanding.
However, they may be purely phantasmal.
These signals may emerge from underlying random noise, with statistics incorrectly “discovering” non-existent patterns.
Only superior data, sufficiently mapping out our Universe, will decide.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
Starts With A Bang is written by Ethan Siegel, Ph.D., author of Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.