# Cosmology

## STELLAR STRUCTURE AND EVOLUTION

## Cosmology and astrophysics

... Ordinary matter dilutes as it expands. According to the second law of thermodynamics, its pressure on

the walls should be positive, which exerts a force, and energy is lost in the expansion. On the other hand, vacuum energy is always the same, independent of the volume of the region, and thus, **according to the second law, its pressure must be negative and of the same magnitude as the energy density.** This negative pressure means that the volume tends to increase more and more rapidly, which explains the exponential expansion of the universe **dominated by a cosmological constant.**

## Cosmic microwave background

https://en.wikipedia.org/wiki/Cosmic_microwave_background

Astronomy 162: Professor Barbara Ryden

https://www.nobelprize.org/uploads/2018/06/wilson-lecture-1.pdf