This visualization of the Laniakea supercluster, which represents a collection of more than 100,000 estimated galaxies spanning a volume of over 100 million light-years, shows the distribution of dark matter (shadowy purple) and individual galaxies (bright orange/yellow) together. Despite the relatively recent identification of Laniakea as the supercluster which contains the Milky Way and much more, it’s not a gravitationally bound structure and will not hold together as the Universe continues to expand. (TSAGHKYAN / WIKIMEDIA COMMONS)

The Largest Structures In The Universe May Not Actually Exist

Which is good, because if they do, they violate the cosmological principle.

In theory, the Universe should be the same, on average, everywhere.

A simulation of the large-scale structure of the Universe. While, on small scales, various regions are dense and massive enough to correspond to star clusters, galaxies, and galaxy clusters, while others correspond to cosmic voids, on larger scales, every location is largely similar to every other location. (DR. ZARIJA LUKIC)

On the largest scales, it shouldn’t matter which direction you observe.

This image shows a map of the full sky and the X-ray clusters identified to measure the expansion of the Universe in a direction-dependent way, along with four X-ray clusters in detail imaged by NASA’s Chandra X-ray observatory. Although the results suggest the Universe’s expansion may not be isotropic, or the same in all directions, the data is far from clear-cut, and the anisotropic interpretation was heavily criticized. (NASA/CXC/UNIV. OF BONN/K. MIGKAS ET AL.)

Nor should it matter which location you’re examining.

In modern cosmology, a large-scale web of dark matter and normal matter permeates the Universe. On the scales of individual galaxies and smaller, the structures formed by matter are highly non-linear, with densities that depart from the average density by enormous amounts. On very large scales, however, the density of any region of space is very close to the average density: to about 99.99% accuracy. (WESTERN WASHINGTON UNIVERSITY)

We expect isotropy and homogeneity, with physical consequences if they’re violated.

The early Universe was full of matter and radiation, and was so hot and dense that the quarks and gluons present didn’t form into individual protons and neutrons, but remained in a quark-gluon plasma. This primordial soup consisted of particles, antiparticles, and radiation, and although was in a lower entropy state than our modern Universe, there was still plenty of entropy. (RHIC COLLABORATION, BROOKHAVEN)

Initially, the Big Bang simultaneously occurred everywhere.