Motion: Truth or Convention

The knowledge that certain physical concepts are relative, rather than absolute, is well-known in the scientific realm, but is also a widely disseminated idea in the lay world. Although Einstein is often assumed to be the originator of the general concept of relativity, the subject had its beginnings with Galileo. Velocity is undoubtedly the simplest quantifiable indicator of motion. However, it has been known for 400 years that the velocity of material bodies is relative rather than absolute. What is not well-known is that for the last 100 years, there has been a debate over whether velocity is also conventional, to wit, not determinable without recourse to some arbitrary prior agreement.