Matter refers to anything that occupies space and has mass. It is the physical substance that constitutes the observable universe. According to classical physics, matter was traditionally understood as composed of particles, such as atoms and molecules, which were thought to be solid, discrete entities.
However, with the advent of quantum mechanics in the early 20th century, scientists discovered that matter can also exhibit wave-like properties. This led to the understanding that particles, like electrons and protons, can behave both as discrete particles and as waves. This duality is known as wave-particle duality.
In quantum mechanics, matter is described by wave functions, which represent the probability distributions of finding particles at different locations or having different properties. The behavior of matter is governed by the principles of quantum mechanics, which include phenomena like superposition (particles existing in multiple states simultaneously) and entanglement (particles being connected in a non-local way).
So, in summary, matter is a broad term that encompasses particles and waves. It can exhibit both particle-like and wave-like characteristics, depending on the context and the experimental conditions. Our current understanding of matter is based on quantum mechanics, which provides a framework for describing its behavior at the microscopic level.