Quantum mechanics
From Conservapedia
Quantum mechanics is the branch of physics that describes the behavior of systems on very small length and energy scales, such as those found in atomic and subatomic interactions. It is essential for understanding certain concepts that classical physics cannot explain, such as the discrete nature of small-scale interactions, wave-particle duality, the uncertainty principle, and quantum entanglement. Quantum mechanics forms the basis for our understanding of many phenomena, including chemical reactions and radioactive decay, as well as all computers and electronic devices today.
Another historical name for "quantum mechanics" was "wave mechanics," which is a more descriptive term because wave equations were developed to describe the position of particles.
Contents |
History
While the roots of quantum mechanics can be traced to experiments performed in the 19th century, the theory began to emerge when Max Planck proposed a "quantum hypothesis" to explain the energy spectrum of black body radiation in 1900. He proposed that the energy of what we now call a photon is proportional to its frequency. In 1905, Albert Einstein also suggested that light is composed of discrete packets (quanta) in order to explain the photoelectric effect. A decade later, Niels Bohr proposed a model of the atom in which angular momentum is quantized. Eventually, the mathematical formalism that became known as quantum mechanics was developed in the 1920s and 1930s by John von Neumann, Hermann Weyl, and others, after Erwin Schrodinger's discovery of wave mechanics and Werner Heisenberg's discovery of matrix mechanics.
Principles
- Every system can be described by a wave function, which is generally a function of the position coordinates and time. All possible predictions of the physical properties of the system can be obtained from the wave function. The wave function can be obtained by solving the Schrodinger equation for the system.
- An observable is a property of the system which can be measured. In some systems, many observables can take only certain specific values.
- If we measure such an observable, generally the wave function does not predict exactly which value we will obtain. Instead, the wave function gives us the probability that a certain value will be obtained. After a measurement is made, the wave function is permanently changed in such a way that any successive measurement will certainly return the same value. This is called the collapse of the wave function.
The uncertainty principle
As a result of the wave nature of a particle, the position of the particle can never be precisely known, given precise knowledge of its velocity. Whenever it is attempted to be measured, knowledge of the electron's velocity is lost. The inverse also applies. Hence, there is an inherent uncertainty that prevents precisely measuring both the position and the momentum simultaneously. This is known as the Heisenberg Uncertainty Principle.
Applications
An important aspect of Quantum Mechanics is the predictions it makes about the radioactive decay of isotopes. Radioactive decay processes, controlled by the wave equations, are random events. A radioactive atom has a certain probability of decaying per unit time. As a result, the decay results in an exponential decrease in the amount of isotope remaining in a given sample as a function of time. The characteristic time required for 1/2 of the original amount of isotope to decay is known as the "half-life" and can vary from quadrillionths of a second to quintillions of years.
See also
Concepts in quantum mechanics
Important contributors to quantum mechanics
External Links
For an excellent discussion of quantum mechanics, see: http://www.chemistry.ohio-state.edu/betha/qm/
