Matter can be converted into energy and vice versa, but it cannot be destroyed in the traditional sense; rather, it transforms into other forms of energy. Matter is defined as a form of energy with mass, and while it has mass, energy also possesses mass, as described by E=mc². The conversion of matter to energy occurs in processes like nuclear fusion and fission, while matter can be formed from energy in rare conditions, such as during the early universe. Conservation of energy holds true over short time scales, but its applicability over long time scales, particularly in an expanding universe, raises complex questions. Ultimately, while matter can change forms, it is not destroyed, aligning with the principles of physics.