Matter

Matter is commonly defined as the substance of which physical objects are composed. It constitutes the observable Universe. According to the theory of relativity there is no distinction between matter and energy, because matter can be converted to energy (see annihilation), and vice versa (see matter creation). Philosophically, matter constitutes the formless substratum of all things, which exists only potentially and from which reality is produced. In the sense of content, matter is also used in contrast to form.