Relation between in physics

Physics is the natural science that investigates matter, its fundamental constituents, motion and behavior in space and time, as well as energy and force. Physics is one of the most basic scientific fields, with the objective of understanding how the universe works.

Physics 

Physics is one of the oldest academic sciences, if not the oldest, because it includes astronomy.  Physics, chemistry, biology and certain aspects of mathematics have been a part of natural philosophy for much of these natural sciences originated as distinct research disciplines during the Scientific Revolution in the seventeenth century. Many interdisciplinary disciplines of investigation, such as biophysics and quantum chemistry, are intertwined with physics, and the boundaries of physics are hazy. New concepts in physics frequently explain fundamental principles explored by other sciences and propose new research directions in these and other academic subjects like mathematics and philosophy.

New technologies are usually paved by discoveries in physics. For example, advancements in electromagnetism, solid-state physics and nuclear physics led directly to the development of new products that have dramatically transformed modern society, such as television, computers, domestic appliances and nuclear weapons; The development of industrialisation was aided by breakthroughs in thermodynamics and the development of calculus was aided by advances in mechanics.

Classical physics

Classical physics refers to a set of physics theories that predate modern, more comprehensive or broadly applicable theories. If a widely accepted theory is deemed modern, and its introduction signified a major paradigm shift, previous theories or new theories based on the older paradigm, are frequently referred to as “classical physics.”

As a result, the concept of a classical theory is context-dependent. When current theories are unnecessarily complex for a given circumstance, classical physical principles are frequently applied. Classical physics usually refers to science before 1900, whereas modern physics refers to physics after 1900 that includes quantum mechanics and relativity.

In physics, the term “classical theory” has at least two different meanings. Classical theory refers to physics theories that do not utilise the quantisation paradigm, such as classical mechanics and relativity, in the setting of quantum mechanics.  Similarly, classical field theories that do not involve quantum mechanics include general relativity and classical electromagnetism. Classical theories are those that obey Galilean relativity in general and special relativity.

Quantum physics

Quantum mechanics is a fundamental physics theory that describes the physical aspects of nature at the level of atoms and subatomic particles.  All quantum physics, including quantum chemistry, quantum field theory, quantum technology and quantum information science, is built on this basis.

Classical physics or the set of theories that existed before quantum mechanics, can describe many features of nature on a large (macroscopic) scale, but it can’t describe them on microscopic (atomic and subatomic) sizes. Most classical physics theories can be derived as an approximation valid at large (macroscopic) scales from quantum mechanics.

Quantum mechanics differs from classical physics in that energy, momentum, angular momentum and other bound system quantities are restricted to discrete values (quantization), objects have both particle and wave characteristics (wave–particle duality) and there are limits to how accurately the value of a physical quantity can be predicted prior to measurement, given a complete set of initial conditions (the uncertainty principle).

Quantum mechanics arose gradually from theories to explain observations that could not be reconciled with classical physics, such as Max Planck’s solution to the black-body radiation problem in 1900 and Albert Einstein’s 1905 paper explaining the photoelectric effect, which explained the correspondence between energy and frequency. These early attempts to comprehend microscopic events, today known as “old quantum theory,” led to Niels Bohr, Erwin Schrödinger, Werner Heisenberg, Max Born and others developing quantum mechanics fully in the mid-1920s. Modern theory is expressed via a variety of mathematical formalisms that have been devised specifically for it. A mathematical entity known as the wave function is used in one of them to offer information in the form of probability amplitudes about what measurements of a particle’s energy, momentum and other physical attributes might yield.

Applications 

Quantum mechanics has been extremely successful in explaining many aspects of our universe, particularly small-scale and discrete quantities and interactions that cannot be explained using traditional approaches. [footnote 4] Quantum mechanics is frequently the only theory capable of revealing the particular actions of the subatomic particles that make up all matter types (electrons, protons, neutrons, photons and others). Quantum mechanics is essential in solid-state physics and materials research.

Modern technology operates on a scale where quantum effects are significant in many ways. Quantum chemistry, quantum optics, quantum computing, superconducting magnets, light-emitting diodes, the optical amplifier and laser, the transistor and semiconductors such as the microprocessor and medical and research imaging such as magnetic resonance imaging and electron microscopy are all important applications of quantum theory. [32] Many biological and physical phenomena, most notably the macromolecule DNA, have explanations based on the nature of chemical bonds.

Difference between quantum physics and quantum mechanics

Quantum mechanics is a branch of quantum physics, which is itself a major subject of science. Quantum physics is a discipline of science that focuses on quantum mechanics, whereas quantum mechanics is the collection of principles that explain the behaviour of matter and energy.

Quantum physics can also predict and describe the attributes of a physical system, whereas quantum mechanics can describe the properties of molecules, atoms, and subatomic particles in terms of their interactions with one other and with electromagnetic radiation. As a result, in terms of application, quantum physics differs from quantum mechanics.

Conclusion

Although the phrases quantum physics and quantum mechanics are sometimes used interchangeably, they are not interchangeable. Quantum physics is a discipline of science that focuses on quantum mechanics, whereas quantum mechanics is the set of principles that explains the behaviour of matter and energy.