

What is Quantum Mechanics?
Quantum mechanics definition states that it is a basic theory in physics that offers a description of the physical attributes of nature at the scale of atoms and subatomic particles. It is the basis of all quantum physics incorporating the following fields:
Quantum chemistry,
Quantum field theory,
Quantum technology, and
Quantum information science
So, what is quantum physics? Well! Quantum physics definition illustrates how everything works: the renowned description we have of the nature of the particles that form matter and the forces with which they interact.
This page explains how quantum mechanics differ from classical physics. Also, we will get to know what quantum mechanics is and who proposed it.
How is Quantum Mechanics different from Classical Physics?
From the above text, we understood that quantum physics considers the properties of nature at the atomic and subatomic particle scale. Now, how it varies from classical physics is still a question mark. So, let us understand the same.
Classical physics:
Classical physics is one of the branches of physics that talk about the collection of theories that existed before the arrival of quantum mechanics, describing several aspects of nature at an ordinary or macroscopic scale only. It indicates that it was not sufficient for describing the properties at small (atomic and subatomic) scales. We can derive most of the theories in classical physics from quantum mechanics as an approximation valid at a large (macroscopic) scale.
But discovering the properties of nature at the atomic/subatomic level still remains a question, for which quantum mechanics came into advent. Now, let us understand the difference between classical and quantum mechanics.
Difference between Classical Physics and Quantum Mechanics
Quantum mechanics vary from classical physics in a way that energy, momentum, angular momentum, and other quantities of a bound system in quantum mechanics are limited to discrete values (quantisation), where objects have features of both particles and waves (wave-particle duality).
Also, there are restrictions to how accurately the value of a physical quantity can be assumed before its measurement, given a full set of initial conditions (the uncertainty principle).
Now, let us go through remarkable differences between classical physics and quantum mechanics:
So, this was the basic variation of classical physics from quantum mechanics. Now, let us understand more about what quantum theory is.
What is The Advent of Quantum Physics
Quantum mechanics arose progressively from theories to explain observations that couldn’t be reconciled with classical physics, Max Planck's solution in 1900 to the black-body radiation problem, and the correspondence between energy and frequency in Albert Einstein's 1905 paper, which explained the photoelectric effect.
These early attempts to understand microscopic phenomena, now known as the "old quantum theory", brought about the full development of quantum mechanics in the mid-1920s by Niels Bohr, Erwin Schrödinger, Werner Heisenberg, Max Born, and others. The contemporary-day theory is formulated in numerous specially developed mathematical formalisms. In one of them, a mathematical entity known as the wave function provides information, in the form of probability amplitudes, approximately what measurements of a particle's energy, momentum, and different physical properties may yield.
Now, let us understand what quantum theory is.
What is Quantum Physics?
Do you know that the concept of the dual nature of light is the main concept of quantum mechanics and why it was brought into the physical world? Well! Quantum theory tells us that both light and matter comprise tiny particles which have wavelike properties associated with them. Light is formed of particles called photons, and matter is composed of particles called electrons, protons, neutrons.
Quantum theory deals with the behaviour of matter and light on the atomic and subatomic scale. Additionally, this theory tries to express and account for the properties of molecules and atoms and their constituents - electrons, protons, neutrons, and other more esoteric particles like quarks and gluons.
But to recognise how things work in the actual world, quantum mechanics ought to be mixed with other factors of physics – principally, Albert Einstein’s special theory of relativity, which explains what occurs whilst things move very fast – to create what are called quantum field theories.
Three different quantum field theories deal with 3 of the 4 fundamental forces by which matter interacts: electromagnetism, which explains how atoms hold collectively; the strong nuclear force, which explains the stability of the nucleus on the heart of the atom; and the weak nuclear force, which explains why a few atoms undergo radioactive decay.
Over the past five decades or so these three theories were added together in a ramshackle coalition called the “standard version” of particle physics. For all the impact that this model is slightly held together with sticky tape, it is the most correctly tested picture of matter’s basic working that’s ever been devised. Its crowning glory came in 2012 with the discovery of the Higgs boson, the particle that offers all other fundamental particles their mass, whose existence was predicted on the basis of quantum field theories as far back as 1964.
Conventional Theories of Quantum Mechanics
Conventional quantum field theories work nicely in describing the outcomes of experiments at high-energy particle smashers, including CERN’s Large Hadron Collider, wherein the Higgs was discovered, which probes matter at its smallest scales. But in case you need to understand how things work in many less esoteric situations – how electrons move or don’t move via a solid cloth and make a material a metal, an insulator, or a semiconductor, for example – things get even more complex.
Some Unresolved Questions on Quantum Mechanics
Do you know that there is no single quantum theory? There are quantum mechanics, the primary mathematical framework that underpins it all, which was first developed in the 1920s through Niels Bohr, Werner Heisenberg, Erwin Schrödinger, and others. It characterises simple things, which include how the position or momentum of a single particle or the group of a few particles changes over time.
The billions upon billions of interactions in these crowded environments require the development of “effective field theories” that gloss over a number of gory details. The difficulty in building such theories is why many important questions in solid-state physics continue to be unresolved – for instance, why at low temperatures a few substances are superconductors that permit modern without electrical resistance, and why we can’t get this trick to work at room temperature.
But underneath some of these practical problems lies a huge quantum mystery. To a primary degree, quantum physics predicts very strange things approximately how matter works that are absolutely at odds with how things appear to work in the actual world. Quantum particles can behave like particles located in a single place, or they can act like waves, dispensed throughout space or in numerous places at once. How they appear seems to rely upon how we choose to measure them, and earlier than we measure, they seem to have no definite properties at all - leading us to an essential conundrum about the nature of basic reality.
This fuzziness results in obvious paradoxes, which include Schrödinger’s cat, wherein, thanks to an uncertain quantum process, a cat is left dead and alive at the same time. But that’s not all. Quantum particles also seem so that they will have an effect on each other instantaneously even when they're some distance far from each other. This, without a doubt, the bamboozling phenomenon is called entanglement, or, in a word coined through Einstein (an incredible critic of quantum theory), “spooky action at a distance”. Such quantum powers are overseas to us but are the basis of rising technologies, including ultra-secure quantum cryptography and ultra-powerful quantum computing.
But as to what all of it means, no one knows. However, we may simply accept that quantum physics explains the material world in terms we find impossible to square with our experience in the larger, “classical” world, while some people believe that there is a more intuitive theory available to discover.
So, we conclude that in all the discoveries of quantum mechanics, there are numerous elephants in the room. For a start, there’s a fourth essential force of nature that so far the quantum theory has been unable to give an explanation for. Gravity remains the territory of Einstein’s general idea of relativity, a firmly non-quantum theory that doesn’t even involve particles. Intensive efforts over many years to bring gravity under the quantum umbrella and so give an explanation for all of the essential physics within one “theory of everything” that have come to nothing.
Meanwhile, cosmological measurements imply that over ninety-five percent of the universe includes dark matter and dark energy, stuff for which we presently haven't any clarification within the preferred version and conundrums which include the extent of the role of quantum physics in the messy workings of life continues to be unexplained. The world is at a few level quanta – however, whether quantum physics is the last word about the world remains an open question.
Facts on Quantum Theory in Physics
Father of Quantum Physics
Niels Bohr and Max Planck are two of the founding fathers of Quantum Theory. Each received a Nobel Prize in Physics for their work on quanta. On the other hand, quantum theory was proposed by Max Planck or Max Karl Ernst Ludwig Planck. He is a German theoretical physicist who originated quantum theory, for which he is considered the father of quantum physics. His premier work made him win the Nobel Prize for Physics in 1918.
However, Einstein is regarded as the third founder of Quantum Theory as he explained light as quanta in his theory of the Photoelectric Effect, for which he also won the Nobel Prize in the year 1921.
Everything in the universe is made up of waves, and particles, as we can see in the image below:
(Image will be uploaded soon)
Quantum mechanics is discrete or quantised.
The term "quantum" is derived from the Latin for "how much" and reflects the instance that quantum models always incorporate something moving in discrete amounts. Therefore, the energy comprised in a quantum field is always in integer multiples of some fundamental energy, like we see in the image below:
(Image will be uploaded soon)
FAQs on Quantum Mechanics
1. What is quantum mechanics in simple terms?
In simple terms, quantum mechanics is the branch of physics that describes the behaviour of matter and energy at the smallest scales, such as atoms, electrons, and photons. Unlike classical physics which governs large objects, quantum mechanics explains that at this micro-level, particles can behave like both waves and particles, and their properties like energy can only exist in discrete, specific amounts called quanta.
2. How does quantum mechanics differ from classical physics?
Quantum mechanics and classical physics describe the universe at vastly different scales and operate on different principles. The key differences are:
- Scale: Classical physics explains the motion and energy of macroscopic objects (like planets or a ball), while quantum mechanics explains the behaviour of microscopic, subatomic particles.
- Energy: In classical physics, energy is continuous. In quantum mechanics, energy is quantized, meaning it exists in discrete, indivisible packets.
- Certainty: Classical physics is deterministic; if you know the initial conditions, you can predict the outcome precisely. Quantum mechanics is probabilistic, governed by the Uncertainty Principle, which states you cannot know a particle's exact position and momentum simultaneously.
- Nature of Matter: In classical physics, objects are either particles or waves. Quantum mechanics introduces wave-particle duality, where particles like electrons can exhibit properties of both.
3. What are the main principles of quantum mechanics?
The fundamental principles that form the basis of quantum mechanics include:
- Quantization: Physical properties such as energy and momentum are not continuous but are restricted to discrete, specific values.
- Wave-Particle Duality: All matter and light exhibit the properties of both particles and waves, depending on how they are measured.
- The Uncertainty Principle: Formulated by Werner Heisenberg, this principle states that it is fundamentally impossible to know certain pairs of a particle's properties, like its exact position and momentum, at the same time.
- Quantum Entanglement: This is a phenomenon where two or more particles become linked in such a way that their fates are intertwined, regardless of the distance separating them.
4. Who is considered the father of quantum physics?
Max Planck is widely regarded as the father of quantum physics. His work in 1900 on black-body radiation introduced the revolutionary idea that energy is emitted and absorbed in discrete packets, or 'quanta'. This concept laid the groundwork for the entire field. Other foundational figures who developed the theory include Niels Bohr, Werner Heisenberg, Erwin Schrödinger, and Albert Einstein.
5. What is the significance of wave-particle duality?
The significance of wave-particle duality is that it is a cornerstone concept that fundamentally changed our understanding of reality at the atomic level. It successfully explains phenomena that classical physics could not, such as the photoelectric effect (where light behaves as particles called photons) and electron diffraction (where electrons behave as waves). This principle forces us to abandon classical intuitions and is essential for describing the structure of atoms and the operation of modern technologies like lasers and electron microscopes.
6. Why is the quantum mechanical model of an atom more accurate than the Bohr model?
The quantum mechanical model is more accurate than the Bohr model because it provides a more complete and realistic description of the atom. While the Bohr model correctly introduced quantized energy levels, it incorrectly depicted electrons in fixed, circular orbits. The quantum mechanical model improves on this by:
- Incorporating wave-particle duality, treating the electron as a wave.
- Using the Uncertainty Principle, it replaces fixed orbits with 'orbitals,' which are three-dimensional regions of probability describing where an electron is most likely to be found.
This approach better explains the complex spectra of multi-electron atoms and the nature of chemical bonds.
7. What are some real-world applications of quantum mechanics?
Quantum mechanics is not just a theoretical concept; its principles are the foundation for many modern technologies we use every day. Some important applications include:
- Lasers: Used in barcode scanners, fiber-optic communication, and medical surgery.
- Semiconductors and Transistors: The building blocks of all modern electronics, including computers, smartphones, and televisions.
- Magnetic Resonance Imaging (MRI): A medical diagnostic tool that uses the quantum properties of atomic nuclei.
- Atomic Clocks: Provide extremely precise timekeeping essential for GPS and global communication.
- Quantum Computing: An emerging field that uses quantum principles like entanglement to perform calculations far beyond the capacity of classical computers.
8. How did Einstein contribute to quantum theory, and why was he critical of it?
Albert Einstein was one of the founders of quantum theory. His 1905 paper explaining the photoelectric effect by proposing that light is made of discrete energy packets (photons) was a pivotal moment in the development of the theory, for which he won the Nobel Prize. However, despite his crucial contributions, Einstein was deeply troubled by the theory's implications, particularly its probabilistic nature and the concept of entanglement, which he famously termed "spooky action at a distance." He believed quantum mechanics was an incomplete theory and that a deeper, deterministic reality lay beneath it.
9. What is the difference between quantum mechanics and quantum physics?
While the terms are often used interchangeably, there is a subtle distinction. Quantum physics is the broad field of science that studies all phenomena at the atomic and subatomic scales. Quantum mechanics refers to the specific mathematical framework and set of foundational principles (like the Schrödinger equation and the uncertainty principle) that are used to describe and predict these phenomena. Essentially, quantum physics is the overall subject, and quantum mechanics is the core theory that underpins it.
10. Why can't we precisely know a particle's position and momentum at the same time?
This limitation is the core of Heisenberg's Uncertainty Principle, and it is a fundamental property of nature, not a flaw in our instruments. The reason lies in the act of measurement itself. To measure a particle's position, you must interact with it, for instance, by bouncing a photon of light off it. This interaction inevitably transfers energy and disturbs the particle, changing its momentum in an unpredictable way. The more accurately you try to pinpoint its position (by using a high-energy photon), the more you disturb its momentum, and vice versa. It's a built-in trade-off at the quantum level.

















