Fundamental Forces

Forces that govern the various interactions between particles. The four fundamental forces, or interactions, are (in order of increasing strength): gravitational force, the weak nuclear force, the electromagnetic force, and the strong nuclear force. The strong and weak nuclear interactions are short-range forces that are effective only within atomic nuclei. The range of the strong force is ~10-15 m and that of the weak force ~10-17 m. In contrast, the electromagnetic and gravitational interactions are long-range forces, their strengths inversely proportional to the square of distance (1/r2). Although the effect of gravitation on particles is far weaker than the electromagnetic force, because matter tends to be electrically neutral, gravitation controls the overall dynamics of planets, stars, and galaxies. According to quantum theories, fundamental forces are conveyed between real particles by means of “virtual” particles called gauge bosons.

In the present-day universe, at common energy levels, the four forces are separate and have different strengths. However, at very high energies (more than ~1011 eV), the weak and electromagnetic forces merge into a single electroweak force. According to Grand Unified Theories (GUT), the strong nuclear and electroweak forces will behave as a single unified force at particle energies in excess of ~1024 eV (~1012 times higher than achievable experimentally). The fundamental forces may be summarized as follows:

  • Gravitational Force – Acts on matter and energy; mediated by graviton; experienced by all particles
  • Electromagnetic Force – Acts on flavor; mediated by γ; experienced by charged particles; component of electroweak force
  • Weak Nuclear Force – Acts on electric charge; mediated by W+, W, and Z0; experienced by quarks and leptons; component of electroweak force
  • Strong Nuclear Force
    • Fundamental – Acts on color charge; mediated by gluons; experienced by quarks and gluons
    • Residual – Mediated by mesons; experienced by hadrons

Some or all content above used with permission from J. H. Wittke.

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