Irreversible momentum is a term used to describe a situation where the velocity of an object cannot be altered. Some synonyms for irreversible momentum include inescapable force, unstoppable motion, unalterable motion, and irretrievable momentum. These terms all convey the idea of a force or momentum that cannot be changed or reversed. Irreversible momentum can be found in many natural phenomena, such as the movement of planets in the solar system or the motion of ocean waves. It can also be observed in social and political situations, where a certain momentum or force cannot be changed or undone. Using synonyms like these can help to add variety and depth to your writing.