Wilbur Holland, age 16, of Columbia, Tenn., for his question:
WHAT IS QUANTUM MECHANICS?
Quantum mechanics is a field of physics that describes the structure of the atom and the motion of atomic particles. It also explains how atoms absorb and give off energy and light, and it clarifies the nature of light.
Quantum mechanics goes beyond the limits of classical physics, which is based on the laws formulated by the English scientist Sir Isaac Newton. It ranks as one of the major scientific achievements of the 1900s.
Quantum mechanics has contributed greatly to the development of such important devices as lasers and transistors. It also has enabled scientists to gain a better understanding of chemical bonds and chemical reactions.
In an atom, tiny particles of negative electrical charge called electrons move in orbits around a nucleus of positive charge. Quantum mechanics shows that the electrons can move only in certain orbits.
Each orbit, called a quantized orbit, has a particular value of energy. When an electron is in a given orbit, it exists at a specific energy level and does not release or absorb energy. An electron remains in this normal state as long as its atom is not disturbed. But if outside forces act on the atom, the electron can change to another quantized orbit.
Scientists once believed light was a wave emitted as a continuous flow. But quantum mechanics explains that light is a stream of separate photons, which have characteristics of both particles and waves.
Quantum mechanics shows that electrons and other atomic particles of matter are also associated with waves. These waves, called matter waves, have a specific wave length. The wave length is inversely proportional to the particles momentum, which is calculated by multiplying the mass of the particle by its velocity.
A German physicist named Max K.E.L. Planck introduced the idea of quanta in 1900 to explain the spectrum of light emitted by certain heated objects. Then in 1905, another German physicist, this one named Albert Einstein, broadened Planck's idea to explain a phenomenon called the photoelectric effect.
In his explanation, Einstein firmly established that light consists of energy particles that have wave properties.
A Danish physicist named Niels Bohr proposed in 1913 the theory of the atom's electron structure. He also showed how atoms radiate light. Scientists call Bohr's work quantum theory to distinguish it from the broader system of quantum mechanics.
Physicists Ervin Schrodinger of Austria and Werner Heisenberg of Germany independently developed forms of quantum mechanics in 1925. Since that year, these forms have been unified into a system and applied to several scientific fields, including chemistry, molecular biology and solid state physics.