The area of physics that studies the behavior and interactions of particles at the atomic and subatomic scales is called quantum physics, or quantum mechanics. Newtonian mechanics and other factors of classical physics are insufficient to explain phenomena at these scales, requiring alternative theories and principles. The main ideas, theories, applications, well-known experiments, and more in the field of quantum physics are covered in this thorough summary.
Table of Contents
Key Principles of Quantum Physics
Quantum physics is founded on several core principles that differentiate it from classical mechanics. These principles include wave-particle duality, quantization, the uncertainty principle, superposition, and entanglement.
Wave-Particle Duality
By AllenMcC. – Own work, CC BY-SA 3.0,
Wave-particle duality is a fundamental concept in quantum mechanics, stating that particles such as electrons and photons exhibit both particle-like and wave-like properties.
- Behavior: Particles can display interference patterns (wave-like behavior) and also discrete impacts or energy exchanges (particle-like behavior).
- Example: Light, for instance, behaves as a wave in phenomena like interference and diffraction, and as a particle in the photoelectric effect, where light ejects electrons from a material.
Quantization
Quantization is that certain physical quantities, such as energy, momentum, and angular momentum, can only take on discrete values rather than any value within a continuous range.
- Behavior: Electrons in an atom are restricted to specific energy levels; they cannot exist between these levels.
- Example: The energy levels of electrons in an atom are quantized, meaning electrons can only occupy specific energy states and transition between them by absorbing or emitting photons of precise energies.
Uncertainty Principle
The uncertainty principle, formulated by Werner Heisenberg, posits that certain pairs of physical properties, such as position and momentum, cannot be simultaneously measured with arbitrary precision.
- Behavior: The more accurately one property (e.g., position) is known, the less accurately the complementary property (e.g., momentum) can be known.
- Example: If the position of an electron is measured with high precision, its momentum cannot be precisely determined, and vice versa.
Superposition
Superposition is a principle where a quantum system can exist in multiple states simultaneously until it is measured.
- Behavior: A particle, like an electron, can exist in a combination of states, described by a wave function that encompasses all possible states.
- Example: Schrödinger’s cat thought experiment illustrates this principle, where a cat in a box can be simultaneously alive and dead until observed.
Entanglement
Entanglement is a phenomenon where particles become interconnected, such that the state of one particle instantaneously influences the state of another, regardless of the distance separating them.
- Behavior: Two entangled particles remain connected, so that the state of one (spin, position, etc.) directly affects the other, no matter how far apart they are.
- Example: If two entangled photons are separated by large distances, measuring the state of one photon instantly determines the state of the other.
Main Concepts and Models
Quantum physics employs different concepts and mathematical models to describe the behavior of particles and systems. These include quantum states, wave functions, operators, and the Schrödinger equation.
Quantum States and Wave Functions
Quantum states are described by wave functions (Ψ), which contain all the information about a system.
- Quantum State: The complete description of a system, representing probabilities of all possible outcomes.
- Wave Function: A mathematical function that encodes the probabilities of a particle’s position, momentum, and other physical properties.
Operators and Observables
Operators are mathematical entities corresponding to physical observables, which are measurable quantities in a quantum system.
- Operators: Mathematical objects that act on the wave function to extract information about physical observables.
- Observables: Quantities like energy, position, and momentum that can be measured in a quantum system.
Schrödinger Equations
Time-dependent Schrödinger equation:
(iℏ ∂Ψ/∂t = Ĥ Ψ)
Where:
- i is the imaginary unit,
- ℏ is the reduced Planck constant,
- Ψ is the wave function,
- t is time,
- Ĥ is the Hamiltonian operator.
Time-independent Schrödinger equation:
(Ĥ Ψ = E Ψ)
Where:
- E is the energy eigenvalue.
