Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Boson, one of the two basic divisions of elementary particles, the basic units of matter and energy. Some bosons, called elementary bosons, are fundamental particles, meaning they cannot be divided into anything smaller. These bosons carry energy between particles of matter, affecting the behavior of matter particles and holding the particles together in larger structures. Mesons are bosons that are made of more than one particle. Bosons are named for Indian physicist Satyendra Bose, who (with German-born American physicist Albert Einstein) developed a set of equations that describe the way bosons behave. See also Elementary Particles.

Bosons fall into two main groups. One group contains the elementary bosons, or bosons that are not made up of other particles. Elementary bosons play a crucial role in transferring energy between the fermions that compose matter. The other group is called the mesons. Mesons are composite particles—that is, they are made up of other particles. Mesons play an important role in holding together the particles in atoms.