Quantum theory


Probability densities corresponding to the wave functions of an electron in a hydrogen atom possessing definite energy levels (increasing from the top of the image to the bottom: n = 1, 2, 3, ...) and angular momenta (increasing across from left to right: s, p, d, ...). Brighter areas correspond to higher probability density in a position measurement. Such wave functions are directly comparable to Chladni's figures of acoustic modes of vibration in classical physics, and are modes of oscillation as well, possessing a sharp energy and, thus, a definite frequency. The angular momentum and energy are quantized, and take only discrete values like those shown (as is the case for resonant frequencies in acoustics)

From Wikipedia, the free encyclopedia

 a branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of the Planck constant. Quantum mechanics departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales

The name quantum mechanics derives from the observation that some physical quantities can change only in discrete amounts (Latin quanta), and not in a continuous (cf. analog) way.

The earliest versions of quantum mechanics were formulated in the first decade of the 20th century. At around the same time, the atomic theory and the corpuscular theory of light (as updated by Einstein) first came to be widely accepted as scientific fact; these latter theories can be viewed as quantum theories of matter and electromagnetic radiation, respectively. Early quantum theory was significantly reformulated in the mid-1920s by Werner HeisenbergMax Born and Pascual Jordan, who created matrix mechanicsLouis de Broglie and Erwin Schrodinger (Wave Mechanics); and Wolfgang Pauli and Satyendra Nath Bose (statistics of subatomic particles). And the Copenhagen interpretation of Niels Bohr became widely accepted. By 1930, quantum mechanics had been further unified and formalized by the work of David HilbertPaul Dirac and John von Neumann,[2] with a greater emphasis placed on measurement in quantum mechanics, the statistical nature of our knowledge of reality, and philosophical speculation about the role of the observer.

the probabilistic nature of quantum mechanics is not a temporary feature which will eventually be replaced by a deterministic theory, but instead must be considered a final renunciation of the classical idea of "causality"

Everything is at the same time a wave and a particle.

New Scientist introduction to quantum world

 It successfully explained phenomena such as radioactivity and antimatter, and no other theory can match its description of how light and particles behave on small scales.

Quantum objects can exist in multiple statesand places at the same time, requiring a mastery of statistics to describe them.

Previous theories allowed atoms to vibrate at any frequency, leading to incorrect predictions that they could radiate infinite amounts of energy - a problem known as the ultraviolet catastrophe.

In 1900, Max Planck solved this problem by assuming atoms can vibrate only at specific, or quantised, frequencies. Then, in 1905, Einstein cracked the mystery of the photoelectric effect, whereby light falling on metal releases electrons of specific energies. The existing theory of light as waves failed to explain the effect, but Einstein provided a neat solution by suggesting light came in discrete packages of energy called photon

light's chameleon-like ability to behave as either a particle or a wave, depending on the experimental setup

Danish physicist Niels Bohr explained this wave-particle duality by doing away with the concept of a reality separate from one's observations. In his "Copenhagen interpretation", Bohr argued that the very act of measurement affects what we observe.

The popular many worlds interpretation suggests quantum objects display several behaviours because they inhabit an infinite number of parallel universes

Heisenberg uncertainty principle, 1927 - one can never know both the position and momentum of a quantum object - measuring one invariably changes the other.

the underlying cause of the duality seen in experiments is a phenomenon called entanglement. Entanglement is the idea that in the quantum world, objects are not independent if they have interacted with each other or come into being through the same process. They become linked, or entangled, such that changing one invariably affects the other, no matter how far apart they are - something Einstein called "spooky action at a distance".

The first teleportation of a quantum state occurred in 1998, and scientists have been gradually entangling more and more particles, different kinds of particles, and large particles.

Teleportation: according to quantum theory, atoms are far less concrete entities, and can be persuaded to interact with each other so that events affecting one instantly affect another—no matter how far apart they are. Dubbed entanglement, this could open the way to superfast quantum communications systems and ways of teleporting objects by instantly transferring their properties from place to place.

Quantum Teleportation

(One of the applications of the quantum theory)

Teleportation is the name given by science fiction writers to the feat of making an object or person disintegrate in one place while a perfect replica appears somewhere else. How this is accomplished is usually not explained in detail, but the general idea seems to be that the original object is scanned in such a way as to extract all the information from it, then this information is transmitted to the receiving location and used to construct the replica, not necessarily from the actual material of the original, but perhaps from atoms of the same kinds, arranged in exactly the same pattern as the original.

In 1993 an international group of six scientists, including IBM Fellow Charles H. Bennett, confirmed the intuitions of the majority of science fiction writers by showing that perfect teleportation is indeed possible in principle, but only if the original is destroyed. In subsequent years, other scientists have demonstrated teleportation experimentally in a variety of systems, including single photons, coherent light fields, nuclear spins, and trapped ions

Quantum theory

It began with the study of the interactions of matter and radiation

In contrast to Einstein's Relativity, which is about the largest things in the universe, quantum theory deals with the tiniest things we know, the particles that atoms are made of, which we call "subatomic" particles

In contrast to Relativity, quantum theory was not the work of one individual, but the collaborative effort of some of the most brilliant physicists of the 20th century, among them Niels Bohr, Erwin Schrödinger, Wolfgang Pauli, and Max Born. Two names clearly stand out: Max Planck (1858-1947) and Werner Heisenberg (1901-1976). Planck is recognised as the originator of the quantum theory, while Heisenberg formulated one of the most eminent laws of quantum theory, the Uncertainty Principle

Around 1900, Max Planck from the University of Kiel concerned himself with observations of the radiation of heated materials… energy is always emitted or absorbed in discrete units, which he called quanta. Planck developed his quantum theory further and derived a universal constant, which came to be known as Planck's constant. The resulting law states that the energy of each quantum is equal to the frequency of the radiation multiplied by the universal constant: E=f*h, where h is 6.63 * 10E-34 Js

Quantum theory

the theoretical basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level

by making the assumption that energy existed in individual units in the same way that matter does, rather than just as a constant electromagnetic wave - as had been formerly assumed - and was therefore quantifiable, he could find the answer to his question

History of the theory:

·         In 1900, Planck made the assumption that energy was made of individual units, or quanta.

·         In 1905, Albert Einstein theorized that not just the energy, but the radiation itself wasquantized in the same manner.

·         In 1924, Louis de Broglie proposed that there is no fundamental difference in the makeup and behavior of energy and matter; on the atomic and subatomic level either may behave as if made of either particles or waves. This theory became known as theprinciple of wave-particle duality: elementary particles of both energy and matter behave, depending on the conditions, like either particles or waves.

·         In 1927, Werner Heisenberg proposed that precise, simultaneous measurement of two complementary values - such as the position and momentum of a subatomic particle - is impossible. Contrary to the principles of classical physics, their simultaneous measurement is inescapably flawed; the more precisely one value is measured, the more flawed will be the measurement of the other value. This theory became known as the uncertainty principle,

Quantum theory and Einstein's theory of relativity form the basis for modern physics

Symphony of Science - the Quantum World!

A song with subs, introduction to quantum theory. Wonderful!

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