Whois & Analysis for asergeev.com

Perturbation theory comprises mathematical methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem.

A critical feature of the technique is a middle step that breaks the problem into "solvable" and "perturbation" parts.

Perturbation theory is applicable if the problem at hand cannot be solved exactly, but can be formulated by adding a "small" term to the mathematical description of the exactly solvable problem.

Quantum mechanics (QM; also known as quantum physics or quantum theory), including quantum field theory, is a branch of physics which is the fundamental theory of nature at small scales and low energies of atoms and subatomic particles.

Classical physics, the physics existing before quantum mechanics, derives from quantum mechanics as an approximation valid only at large (macroscopic) scales.

Quantum mechanics differs from classical physics in that energy, momentum and other quantities are often restricted to discrete values (quantization), objects have characteristics of both particles and waves (wave-particle duality), and there are limits to the precision with which quantities can be known (Uncertainty principle).

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.

Molecules are distinguished from ions by their lack of electrical charge.

However, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions.

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.

Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms.

Atoms are very small; typical sizes are around 100 picometers (a ten-billionth of a meter, in the short scale).

An image (from) is an artifact that depicts visual perception, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person, thus providing a depiction of it.