View source for The Physics of Quantum Mechanics

== Introduction ==

Quantum mechanics is a branch of [[Physics|physics]] that deals with phenomena on a very small scale, such as molecules, atoms, and subatomic particles like electrons and photons. It is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales. 

[[Image:Detail-18850.jpg|thumb|center|A close-up view of a complex mathematical equation representing quantum mechanics.|class=only_on_mobile]]
[[Image:Detail-18851.jpg|thumb|center|A close-up view of a complex mathematical equation representing quantum mechanics.|class=only_on_desktop]]

== Historical Development ==

The development of quantum mechanics was initially motivated by two scientific observations which could not be explained by classical physics, namely the [[Blackbody Radiation|blackbody radiation]] and the photoelectric effect. The term "quantum" itself originates from the Latin word for "how much" and reflects the fact that quantum models always involve something coming in discrete amounts. The theory of quantum mechanics began with Max Planck's discovery in 1900 that light-energy, in certain situations, can exhibit characteristics of physical matter.

== Principles of Quantum Mechanics ==

Quantum mechanics is based on several key principles which are fundamentally different from those of classical physics. These principles include wave-particle duality, superposition, and uncertainty.

=== Wave-Particle Duality ===

The principle of wave-particle duality asserts that all particles exhibit both wave and particle properties. A central concept of quantum mechanics, this duality addresses the inability of classical concepts like "particle" and "wave" to fully describe the behavior of quantum-scale objects.

[[Image:Detail-18852.jpg|thumb|center|A representation of a particle exhibiting both wave-like and particle-like properties.|class=only_on_mobile]]
[[Image:Detail-18853.jpg|thumb|center|A representation of a particle exhibiting both wave-like and particle-like properties.|class=only_on_desktop]]

=== Superposition ===

The principle of superposition states that any two (or more) quantum states can be added together, or "superposed", and the result will be another valid quantum state; and conversely, that every quantum state can be represented as a sum of two or more other distinct states. This principle is directly tied to the concept of wave-particle duality.

=== Uncertainty Principle ===

The uncertainty principle, formulated by Werner Heisenberg, is one of the fundamental principles of quantum mechanics. It states that the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory. The very concepts of exact position and exact velocity together, in fact, have no meaning in nature.

[[Image:Detail-18854.jpg|thumb|center|An illustration of the uncertainty principle in action.|class=only_on_mobile]]
[[Image:Detail-18855.jpg|thumb|center|An illustration of the uncertainty principle in action.|class=only_on_desktop]]

== Quantum Mechanics and Classical Physics ==

Quantum mechanics and classical physics are the two main theories in the field of physical science. Classical physics, the description of physics existing before the formulation of the theory of relativity and quantum mechanics, describes nature at ordinary (macroscopic) scale. Quantum mechanics, on the other hand, deals with phenomena on a very small (quantum) scale.

== Applications of Quantum Mechanics ==

Quantum mechanics has been instrumental in understanding the behavior of particles at the atomic and subatomic level. It has applications in various fields such as chemistry, electronics, computer science, and even biology. 

=== Quantum Mechanics in Chemistry ===

Quantum mechanics plays a crucial role in chemistry. It helps in understanding the behavior of particles at the molecular and atomic level. It is the basis for understanding the bonding of atoms to form molecules and their interactions.

=== Quantum Mechanics in Electronics ===

Quantum mechanics is essential in electronics for understanding how electrons move through a semiconductor. Quantum mechanics is also necessary for the understanding and design of many types of modern electronic devices such as transistors and semiconductors found in modern computers.

[[Image:Detail-18856.jpg|thumb|center|A quantum computer in a laboratory setting.|class=only_on_mobile]]
[[Image:Detail-18857.jpg|thumb|center|A quantum computer in a laboratory setting.|class=only_on_desktop]]

=== Quantum Mechanics in Computer Science ===

Quantum mechanics has also found applications in computer science, with the development of quantum computing. Quantum computers use quantum bits, or "qubits", which can be in a superposition of states, unlike classical bits that are either in a state of 0 or 1.

=== Quantum Mechanics in Biology ===

Quantum mechanics has also been used to explain various phenomena in biological systems, like the process of photosynthesis, the sense of smell, and even the behavior of birds.

== Conclusion ==

Quantum mechanics, with its principles of superposition, wave-particle duality, and uncertainty, has revolutionized our understanding of the physical world at the smallest scales. Its applications are vast and varied, from chemistry and electronics to computer science and biology.

== See Also ==

* [[Quantum Field Theory]]
* [[Quantum Computing]]
* [[Quantum Chemistry]]

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