Fundamentals

Quantum Mechanics: The Physics of the Microscopic World

A fundamental theory in physics that describes the physical properties of nature at the scale of atoms and subatomic particles.

QWiki Team 2 min read
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Introduction

Quantum mechanics 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 is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.

History and Key Postulates

Classical physics, which describes the universe at human scales, fails when applied to subatomic particles. In the late 19th and early 20th centuries, physicists discovered that energy, momentum, angular momentum, and other quantities of a bound system are often restricted to discrete values (quantization).

Key postulates include:

  • Wavefunction Representation: The state of a physical system is represented by a wave function ψ(x,t)\psi(x,t), which contains all knowable information about the system.
  • Born Rule: The probability of finding a particle at a given position is proportional to the square magnitude of its wavefunction ∣ψ(x,t)∣2|\psi(x,t)|^2.
  • Schrödinger Equation: The temporal evolution of the wavefunction is governed by the Schrödinger equation: iℏ∂∂tψ(x,t)=H^ψ(x,t)i\hbar \frac{\partial}{\partial t}\psi(x,t) = \hat{H}\psi(x,t)

Key Phenomena

  1. Quantization: Energy levels are discrete. Electrons in an atom inhabit specific shells rather than a continuous spectrum.
  2. Superposition: Systems can exist in multiple physical states simultaneously until a measurement is performed.
  3. Entanglement: Multiple particles can link states in a way that remains correlated over arbitrary distances.
  4. Tunneling: Particles can pass through barriers that they lack the classical energy to surmount.