quantity

interaction strength

A parameter that quantifies the magnitude of the force or coupling between particles in a system.
7 related articles

Description

Interaction strength is a fundamental parameter in physics that quantifies how strongly particles or systems influence each other. It determines the probability of interactions, the rates of reactions, and the stability of bound states. In particle physics, it distinguishes the weak, electromagnetic, and strong forces; in condensed matter, it governs phenomena like superconductivity and magnetism. The concept is central to understanding everything from the binding of quarks inside protons to the behavior of dark energy in cosmology.

History

The concept evolved from classical force laws, but the modern understanding emerged with quantum field theory in the mid-20th century, particularly through the work of Feynman, Schwinger, and Tomonaga on quantum electrodynamics.

How it works

In quantum field theory, interaction strength is encoded in coupling constants, which appear in the mathematical terms that describe how particles exchange force carriers. A larger coupling constant means more frequent or more intense interactions. In many systems, the strength can vary with energy scale—a phenomenon known as running coupling—which explains why the strong force becomes weak at high energies and strong at low energies. In statistical mechanics, interaction strength controls phase transitions, determining whether a system orders or remains disordered.

In practice

Used to design materials with tailored magnetic or electronic properties, and to predict particle collision outcomes at accelerators like the LHC.

Fun fact

The interaction strength of the strong nuclear force is so large that it confines quarks permanently inside protons, yet it becomes so weak at high energies that quarks behave as free particles—a phenomenon called asymptotic freedom.

Concept graph →

Related articles · 7

Chemical Physics2026-08-032 minarXiv:2608.02865express
Weak Molecular Bonds Step Out of the Shadows
Inside every cell, things are constantly meeting and parting. Some pairs hold tight, like Velcro, while others barely touch, like pollen on the wind. These fleeting touches, where the binding strength is comparable to a grain of salt dissolving in a glass of water, govern many of the cell's signals and decisions.
HEP Phenomenology2026-07-242 minarXiv:2607.21952express
Locked Up Forever: How Physicists Measured the Force That Holds Quarks
The proton is not a solid ball but a tiny prison. Inside it, three quarks are locked up, and the gluon field keeps them from escaping — something like invisible threads that only grow stronger if the quarks try to move apart.
HEP Phenomenology2026-05-272 minarXiv:2605.28248express
Dark matter tugs at satellites like invisible strings
A stone thrown into water leaves ripples. A satellite orbiting Earth also leaves a trace — not on water, but in the laws of physics. Its orbit is not a frozen line: it slowly rotates, like the hand of a giant clock.
Cosmology2026-05-151 minarXiv:2605.16155express
Dark Dialogue: Gravitational Lenses Reveal an Exchange of Matter and Energy
The Universe is a vast city. In it, dark matter is the invisible framework of buildings, and dark energy is the force stretching the streets. For a long time they were considered independent, but new research has caught them in secret communication.
HEP Phenomenology2026-05-012 minarXiv:2605.00339express
How to Keep Quarks Inside a Proton
If you try to break a proton apart and pull out a quark, you're in for a surprise. Ordinary forces, like the electric force, weaken as particles fly apart. Here, it's the opposite. The farther a quark gets from its neighbors, the harder it's pulled back.
Quantum Physics2026-04-242 minarXiv:2604.22593express
Invisible Obstacles in the Hunt for Quantum Gravity
Physicists are trying to hear a whisper in a noisy room. They build a soundproof booth, but even inside, their own breathing and heartbeat create interference. That's roughly how the search for quantum gravity goes: they want to see gravity bind two particles into a single whole — entangle them.
Nuclear Theory2026-02-031 minarXiv:2602.03388express
Neutron Stars Get Heavier Thanks to Invisible Particles
Inside a neutron star, matter is squeezed so tightly that a single teaspoon weighs as much as a mountain. Under such pressure, ordinary particles, protons and neutrons, can transform into exotic particles known as hyperons. These particles resemble neutrons but contain strange quarks.