A Thousand Problems in Cosmology: Horizons
  This is one chapter of the collection of problems in cosmology, in which we
assemble the problems, with solutions, that concern one of the most distinctive
features of general relativity and cosmology---the horizons.
  The first part gives an elementary introduction into the concept in the
cosmological context, then we move to more formal exposition of the subject and
consider first simple, and then composite models, such as $\Lambda$CDM. The
fourth section elevates the rigor one more step and explores the causal
structure of different simple cosmological models in terms of conformal
diagrams. The section on black holes relates the general scheme of constructing
conformal diagrams for stationary black hole spacetimes. The consequent parts
focus on more specific topics, such as the various problems regarding the
Hubble sphere, inflation and holography.
  The full collection is available in the form of a wiki-based resource at
universeinproblems.com. The cosmological community is welcome to contribute to
its development.
