Quantum mechanics

Quantum mechanics is a branch of physics that deals with matter on the smallest known scales. While debate still exists within the scientific community as to the field’s precise definition, physicists generally agree that quantum mechanics begins when scientific inquiry extends beyond the atomic and subatomic levels and enters the realm of nanoscales—the tiniest units of measurement yet devised. Alternately known as quantum physics or quantum theory, quantum mechanics is inhabited by abstract mathematical equations and pliable principles that often seem to be at odds with the laws of classical physics.

The Development of Quantum Mechanics

Quantum mechanics arose from advancements in chemistry, particularly those made during the nineteenth and twentieth centuries when chemists discovered and arranged the elements in the periodic table and identified and studied atomic structures. In the late nineteenth century, scientists determined that atoms themselves are comprised of even smaller particles and that subatomic structures are dominated by two major phenomena: waves and particles. In physics, a wave is an energy-based entity that moves from one place to another through a specific medium such as space. A particle is a matter-based entity existing in a localized area with quantifiable characteristics including size, volume, and mass.

These discoveries were revolutionary and forced physicists to rethink their understanding of small-scale physics. This, in turn, gave rise to a new generation of concepts and theories that attempted to explain the observed behaviors and properties of subatomic waves and particles. First emerging between 1900 and 1930, this new field of inquiry came to be known as quantum mechanics.

Key Principles in Quantum Mechanics

While quantum mechanics has grown to encompass a broad and complex range of concepts and theories, it largely arose from two foundational principles: quantized properties and the relationship between particles and waves. In addition to these bases, the development of quantum mechanics was also heavily influenced by the famous Schrodinger Equation, as well as a theory known as the Heisenberg Uncertainty Principle. These advancements coincided with Albert Einstein’s revolutionary theory of relativity, a mathematical system that attempted to explain the movement of objects traveling at extremely high speeds.

The concept of quantized properties upended a longstanding principle of classical mechanics, which held that the physical characteristics of an object, such as its position, its color, and the speed of its motion, were bound to a continuum. Discoveries in the field of quantized properties found that these attributes do not always conform to a smooth, flowing, and continuous pattern but sometimes abruptly “jump” from one quantity to another. This idea is most readily demonstrated by examining the behavior of subatomic particles, which were previously thought to orbit an atom’s nucleus in a smooth and unbroken route. Scientists subsequently discovered that these particles sometimes “jumped” from one position to another, rather than continuously proceeding along a predetermined orbital path.

The boundaries between waves and particles, two objects that were previously believed to be discrete and mutually exclusive phenomena, also became blurred. For example, early researchers found that energy-based waves of light sometimes behaved more like matter-based particles, and particles sometimes displayed the physical characteristics of waves. As a result, quantum physicists began to consider particle properties and wave properties as different manifestations of a single underlying idea: that there is no functional distinction between the energy of a wave and the matter of a particle at the subatomic level. This idea was codified into a unifying theory known as the Principle of Wave-Particle Duality.

Scientists began to search for a way to explain the unpredictability of subatomic wave and particle behaviors, which led to the Schrodinger Equation. The Schrodinger Equation remains one of the single most important ideas in the field of quantum mechanics, and entire volumes have been dedicated to examining its intricacies and complexities. At its most basic level, the equation is actually made up of two different mathematical formulas, both of which attempt to predict the behavior of a waveform. One equation is time-based while the other is time-independent.

The Schrodinger Equation is closely tied to the Heisenberg Uncertainty Principle, which describes the limitations of quantum mechanics. While the Schrodinger Equation proved useful in predicting the behaviors of subatomic waveforms, scientists increasingly found that the very study of subatomic particles influenced their activity. As such, there were limits to the degree of certainty scientists could have in regard to their findings. The Heisenberg Uncertainty Principle attempted to define and correct for these disturbances, thus realigning scientific observations to more closely conform to what would likely have happened if outside events had never affected the subatomic structure.

Such ideas were revolutionary when they were first forwarded in the early part of the twentieth century, and it took years for them to become widely accepted within the scientific community. However, after decades of continued research, they remain central concepts in the field of quantum mechanics.

Major Figures in the Development of Quantum Mechanics

While Albert Einstein is often associated with quantum mechanics, he actually had only a peripheral and indirect influence on its development. The field was pioneered by a group of physicists including J.J. Thompson, Max Planck, Louis de Broglie, Erwin Schrodinger, and Werner Heisenberg.

J.J. Thompson (1856-1940) was an English scientist credited with the 1897 discovery of electrons. His findings signaled that there were, in fact, particles smaller than atoms. The German physicist Max Planck's (1858-1947) groundbreaking studies of light beams and wave motion helped him capture the 1918 Nobel Prize in Physics. Louis de Broglie (1892-1987), a French scientist, is credited with formulating the Principle of Wave-Particle Duality, which remains a central concept in quantum mechanics. The Austrian-born scientist Erwin Schrodinger (1887-1961) and the German physicist Werner Heisenberg (1901-1976) contributed two of the field’s defining principles. Schrodinger’s famous equation continues to largely form the basis of inquiry into quantum physics, and while contemporary researchers have been debating the merits of the Heisenberg Uncertainty Principle, its development was a watershed moment in the evolution of the discipline.

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