thumb|upright=0.85|Rapidity is the value of for velocity and speed of light
thumb|upright=0.85|Rapidity is the value of for velocity and speed of light
In special relativity, the classical concept of velocity is converted to rapidity to accommodate the limit determined by the speed of light. Velocities must be combined by Einstein's velocity-addition formula. For low speeds, rapidity and velocity are almost exactly proportional but, for higher velocities, rapidity takes a larger value, with the rapidity of light being infinite.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).