Electromagnetic interaction

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The electromagnetic interaction is one of the four basic forces in physics . Like gravity , it is easy to experience in everyday life, which is why it has long been researched in depth and has been well understood for over 100 years. The electromagnetic interaction is responsible for most everyday phenomena such as light , electricity and magnetism . Together with the exchange interaction, it determines the structure and properties of atoms , molecules and solids .


The starting point of the research was an investigation of the forces between electrical charges . The law of Coulomb of about 1785 is this force between two point-like charges very similar to the law of gravity to. The effect of electric forces on distant charges is described by the concept of the electric field . This is not only caused by electrical charges, but also by changes in magnetic fields over time . This finding is mainly due to Michael Faraday . While static electrical charges apparently have nothing to do with the phenomena of magnetism, a moving electrical charge turns out to be the cause of a magnetic field, as Hans Christian Ørsted recognized in 1820. If a second charge moves in this field, it experiences a magnetic force according to the laws of classical electrodynamics , which is about as great as the electric force when the relative speed is in the order of magnitude of the speed of light . Classical electrodynamics is the first example of a field theory that fulfills Einstein's principle of relativity. If electrodynamics were only invariant to Galileo transformations , then there would be no induction phenomena and no propagation of electromagnetic waves.

The theory of classical electrodynamics goes back to James Clerk Maxwell , who in the 19th century recognized the laws of electricity, magnetism and light as different aspects of a fundamental interaction, electromagnetism , in the Maxwell equations named after him . The electromagnetic interaction, which is itself the result of the summary of the theory of electrical and magnetic interaction, has been described together with the weak interaction as an electroweak interaction since 1967 . The aim is to integrate the strong interaction into the common unified field theory .


It is characteristic of the electromagnetic interaction that it has a large (in principle infinite) range and at the same time is saturable, i.e. H. the effect of a negative and a positive charge on a distant third charge practically cancel each other out. The strength of the electromagnetic interaction is determined by the fine structure constant , this coupling constant is about a factor of 100 smaller than that of the strong interaction, but several orders of magnitude larger than that of the weak interaction and a lot larger than that of gravity.

Properties of electromagnetism may also be observable when no electric charge is present in tangible distance, such as the electromagnetic waves or the decay of the - pion in two gamma - photons .

In the area of ​​the smallest particles, the electromagnetic interaction is described by quantum electrodynamics . The electromagnetic potentials are understood as field operators, through which the photons, the interaction particles of the electromagnetic interaction, are generated or destroyed. This clearly means that the interaction between charged particles, i.e. the exchange of momentum and energy, is the result of the exchange of photons between these particles.

Classification of the electromagnetic interaction

Fundamental interactions and their descriptions
Strong interaction Electromagnetic interaction Weak interaction Gravity
classic Electrostatics & magnetostatics ,
Newton's law of gravitation ,
general relativity
( standard model )
Quantum electrodynamics Fermi theory Quantum gravity  ?
Electroweak Interaction
( Standard Model )
Big Unified Theory  ?
World formula ("theory of everything")?
Theories at an early stage of development are grayed out.