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Schrödinger equation

physical science Maturity 7-9 Next article →

The Schrödinger equation is a fundamental partial differential equation in quantum mechanics. It describes how the wave function of a non-relativistic quantum system changes over time. In classical physics, we use Newton's second law to predict the path of an object. The Schrödinger equation serves as the quantum counterpart to that law. Instead of predicting a specific path, it predicts the evolution of a wave function. This function characterizes an isolated physical system. Understanding this equation is essential for modern physics and chemistry.

Erwin Schrödinger (1933)
Erwin Schrödinger (1933)

To understand how the equation works, one must look at the wave function, often denoted by the Greek letter psi. This function assigns a complex number to every point in space and time. The equation relies on two main types of energy. The first is kinetic energy, which relates to the motion of the particle. The second is potential energy, which represents the environment or forces acting on the particle. By combining these into a mathematical operator called the Hamiltonian, scientists can solve the equation. The result shows how the wave function evolves.

Wavepacket-a2k4-en
Wavepacket-a2k4-en

There are two main versions of the equation used by physicists. The first is the time-dependent Schrödinger equation. This version describes how a system changes as time passes. The second is the time-independent Schrödinger equation. This is a special case used when the Hamiltonian does not change with time. This version is an eigenvalue equation. It helps scientists find stationary states. These states are like standing waves that do not change their overall form over time.

StationaryStatesAnimation
StationaryStatesAnimation

Quantum mechanics can be studied through different mathematical frameworks. One approach is wave mechanics, which uses the Schrödinger equation. Another is matrix mechanics, which was introduced by Werner Heisenberg. A third is the path integral formulation, developed largely by Richard Feynman. The Schrödinger equation is specifically non-relativistic. This means it treats space and time differently. It uses a first derivative for time and a second derivative for space. This is an approximation that works well for many situations but lacks the symmetry of relativity.

QuantumHarmonicOscillatorAnimation
QuantumHarmonicOscillatorAnimation

History shows how these ideas grew through collaboration and refinement. Erwin Schrödinger, an Austrian physicist, postulated the equation in 1925. He published his findings in 1926. His work was based on a postulate by Louis de Broglie. De Broglie suggested that all matter has an associated matter wave. Schrödinger's equation successfully predicted the bound states of atoms. This matched what scientists saw in experiments. For this massive contribution, Schrödinger received the Nobel Prize in Physics in 1933.

Erwin Schrödinger (1933)
Erwin Schrödinger (1933)

Later scientists worked to fix the limits of the original equation. Paul Dirac incorporated special relativity into quantum mechanics. He created the Dirac equation. This equation uses a single derivative for both space and time. It also describes particles with a property called spin-1/2. Another equation, the Klein–Gordon equation, was also a relativistic wave equation. However, it faced problems with probability density. The density could sometimes be negative, which is physically impossible. Dirac fixed this by using Dirac matrices.

Infinite potential well
Infinite potential well

In a modern context, the equation is part of a larger mathematical structure. The state of a system is defined as a vector in a complex Hilbert space. This space can change depending on what is being studied. For example, describing position and momentum requires a specific type of function space. Physical quantities like energy or spin are represented by operators. When we measure a system, the result is an eigenvalue. The probability of getting that result is determined by the Born rule. This rule uses the square of the wave function's absolute value.

Hydrogen Density Plots
Hydrogen Density Plots

Finally, the equation possesses the important property of linearity. This means that if two different wave functions are solutions, their sum is also a solution. This allows for the existence of quantum superposition. Superposition means a system can exist in a combination of different states at once. The equation also maintains unitarity. This ensures that the total probability of all possible outcomes always stays equal to one. This mathematical consistency is vital for the reliability of quantum mechanics. It connects the tiny world of atoms to the broader laws of the universe.

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🖼️ Images & Media (7)
File:Wavepacket-a2k4-en.gif
Wavepacket-a2k4-en.gif
File:StationaryStatesAnimation.gif
StationaryStatesAnimation.gif
File:Infinite potential well.svg
Infinite potential well.svg
File:QuantumHarmonicOscillatorAnimation.gif
QuantumHarmonicOscillatorAnimation.gif
File:Hydrogen Density Plots.png
Hydrogen Density Plots.png
File:Erwin Schrödinger (1933).jpg
Erwin Schrödinger (1933).jpg
File:Grave Schroedinger (detail).png
Grave Schroedinger (detail).png
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