authorities are entities that we place in society to resolve conflicts and establish trust between humans. These conflicts usually arise in value-bearing interactions, often as a result of scarcity. There is only so much gold in the world, therefore it bears value, and therefore when dealing with gold, we reside to needing an authority. See Need For Trust.
Blockchain systems essentially can act as digital authorities, and can be modeled in any of the ways described in Blockchain Models.