The **key difference** between quantum physics and quantum mechanics is that** quantum physics is a branch of science that focuses on quantum mechanics whereas quantum mechanics is the set of principals used to explain the behaviour of matter and energy.**

People use the terms ‘quantum physics’ and ‘quantum mechanics’ with different meanings. Although we sometimes use these terms to describe the same thing, there is a difference between quantum physics and quantum mechanics. We can identify quantum physics as a branch of science that study theories like quantum mechanics and quantum field theory. In other words, mechanics is a set of theories we study in the branch of science known as physics.

### CONTENTS

1. Overview and Key Difference

2. What is Quantum Physics

3. What is Quantum Mechanics

4. Side by Side Comparison – Quantum Physics vs Quantum Mechanics in Tabular Form

5. Summary

## What is Quantum Physics?

Quantum physics is a branch of science that focuses on systems explained by theories such as quantum mechanics and quantum field theory. Scientists and researchers focus on this area in order to use this knowledge to understand the behaviour of particles at the subatomic level. However, sometimes we use the terms “quantum physics” and “quantum mechanics” interchangeably.

## What is Quantum Mechanics?

Quantum mechanics is the set of principle that explains the behaviour of matter at atomic (or subatomic) scale. The word ‘quantum’ itself describes a fundamental concept of quantum mechanics – the quantized or discrete nature of matter and energy.

Quantum mechanics was born when Max Plank introduced the concept of quantized energy (E =nhf) to explain the blackbody thermal radiation. Then, Einstein came up with the concept of ‘photon’ to explain the particle nature of light. It led to a theory known as ‘wave-particle duality’, which describes the possession of both ‘wave’ and ‘particle’ qualities by matter and energy. Louis de Broglie introduced this concept.

Fundamental concepts of quantum mechanics also include Bohr models to describe atomic structure by Niels Bohr, Schrödinger equation (widely used equation to calculate quantum waves) by Erwin Schrödinger, uncertainty principle (which explains the probabilistic nature of matter and energy) by Werner Heisenberg, and Pauli Exclusion Principle by Wolfgang Pauli. The explanation known as Copenhagen interpretation and the phenomenon known as quantum entanglement also belong to the quantum mechanics.

## What is the Difference Between Quantum Physics and Quantum Mechanics?

Quantum physics is a major branch of science while quantum mechanics is a branch of quantum physics. So, the key difference between quantum physics and quantum mechanics is that quantum physics is a branch of science that focuses on quantum mechanics whereas quantum mechanics is the set of principals that explain the behaviour of matter and energy.

Furthermore, quantum physics can predict and describe the properties of a physical system while quantum mechanics can describe properties of molecules, atoms and subatomic particles regarding the interactions between them and with electromagnetic radiation. Therefore, this is the difference between quantum physics and quantum mechanics in terms of their usage.

## Summary – Quantum Physics vs Quantum Mechanics

Although we use the terms quantum physics and quantum mechanics interchangeably, they are different from each other. The key difference between quantum physics and quantum mechanics is that quantum physics is a branch of science which focuses on quantum mechanics whereas quantum mechanics is the set of principals that explains the behaviour of matter and energy.

##### Reference:

1. Squires, Gordon Leslie. “*Quantum Mechanics*.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 3 Aug. 2018, Available here.

##### Image Courtesy:

1. “3871213” (CC0) via Pixabay

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