To understand what Americans are experiencing with this winter blast, we need to look more than 20 miles above the surface of Earth, to the stratospheric polar vortex.
The Lambda Cold Dark Matter (Lambda CDM) model is the current cosmological model and explains much of what we see in the cosmos. One of Lambda CDM's core features is the prediction that structure grows hierarchically from the bottom up. It begins with dark matter density fluctuations, then dwarf galaxies form, then those dwarfs merge to form more massive galaxies, which merge into still larger galaxies. Eventually, there are galaxy clusters.

