> why do we consider the first instants of the universe maximally ordered Much higher ordering is straightforward and is essentially just statmech: 1. Run the

> why do we consider the first instants of the universe maximally ordered Much higher ordering is straightforward and is essentially just statmech: 1. Run the expansion history of the universe backwards: there are fewer degrees of freedom as the universe collapses into the big bang. 2. Run the expansion history of the universe forwards: vacuum is very high entropy (you can swap a bit of vacuum from here with a bit of vacuum from there and not tell the difference), and there is much more of it at late epochs. Assuming no-hair, black holes are also very high entropy, and there are more of them at later epochs. Maximal ordering makes some assumptions about quantum gravity with respect to (1): > A near homogeneous sea of per-subatomic particles ... would expand in such a way that the universe would remain (nearly) perfectly smooth at all epochs. We can start with the idea that there is an inherent uncertainty to the energy of empty-of-particles space. At later epochs, this uncertainty is small; but in the very early universe it is large. With slow expansion, the uncertainties average out over short distances. However, during cosmic inflation, the uncertainties are stretched and only average out on much larger length scales. The "new" vacuum produced as inflation continues has prorgressively less energy uncertainty, but are "within" the streched uncertainties from earlier. By the time inflation ends, random regions of all sizes contain subregions of overdense and underdense vacuum energy. Cosmic inflation precedes the hot big bang: it is the chaotic arrangement of vacuum energy at different densities that decays into matter (in the most general sense of matter) proportional to the vacuum energy density. More matter arises in the overdense regions than in the underdense regions. As expansion progresses, gravitation takes over: light finds it easier to leave underdense regions than overdense regions, and that (the gravitational redshift, and the spectrum being highly similar to blackbody radiation) means underdense regions look slightly hotter than average regions, and overdense regions look slightly colder. Gravitation also works on the rest of matter too, not just light: matter flows from underdense regions to denser regions; matter flows to overdense regions from sparser regions. Finally, overly-overdense regions will heat up and emit light and kick hot particles out. The balances between the vacuum energy fluctuations before the hot big bang and the gravitation-vs-radiation flow of matter afterwards are encoded in the cosmic microwave background. > less ordered than the universe of galaxies and stars and hydrogen atoms with cold areas in between The mostly-empty areas in between have much higher entropy, and those areas are even bigger (and emptier) at later times. The galaxies and stars and hydrogen atoms are not more numerous at later times: matter dilutes away with expansion.