What phenomenon occurs when matter and antimatter collide?

When matter and antimatter collide, they undergo a process known as annihilation. During this phenomenon, the particles of matter and their corresponding antiparticles—such as electrons and positrons—interact and convert their mass into energy, as described by Einstein's famous equation, E=mc². This process typically results in the production of high-energy photons, such as gamma rays.

This annihilation reaction is incredibly efficient; it releases energy at a higher ratio than nuclear reactions or chemical reactions, making it a significant topic of study in both theoretical physics and practical applications like particle physics research and potential future energy sources. The interactions of matter and antimatter provide insights into fundamental questions about the universe, including why there is an abundance of matter over antimatter.

The other options do not accurately describe the fundamental interactions that occur in an antimatter-matter collision. Fusion typically describes the combination of light elements to form heavier ones, while the formation of stable compounds and a complete cessation of existence without effects are both inaccurate representations of the events that unfold in such collisions.