Relativity Principles and Theories from Galileo to Einstein

Motion is always relative to something. Is this thing a concrete body like the earth, is it an abstract space, or is it an imagined frame? Do the laws of physics depend on the choice of reference? Is there a choice for which the laws are simplest? Is this choice unique? Is there a physical cause for the choice made?

These questions traverse the history of modern physics from Galileo to Einstein. The answers involved Galilean relativity, Newton's absolute space, the purely relational concepts...