Four Fundamental Interactions Mediated by Boson Particles (i.e., Force Carriers)


Electromagnetic Interactions ⇒ Quantum Electrodynamics (QFD)

  • Mediated by photons and occurs between electrically charged particles
  • Also referred to as the electromagnetic force or Lorentz force
  • Usually exhibits electromagnetic fields (e.g., electric fields, magnetic fields, light)

Weak Interactions ⇒ Quantum Flavourdynamics (QFD)

  • Mediated by \mathrm{W} and \mathrm{Z} bosons
  • Weak interactions are the mechanism of interaction between subatomic particles causing radioactive decay
    • Plays an essential role in nuclear fission (i.e., atomic nuclie breaking apart)
  • Often described in terms of electro-weak theory (EWT) since EWT best describes weak force
  • Only takes place at small, sub-atomic distance (less than the diameter of a proton)

Strong Interactions ⇒ Quantum Chromodynamics (QCD)

  • Mediated by gluons (massless particles) and occurs between quarks, hadrons (composed of quarks), antiquarks, and other gluons
  • We use color charge to best describe the way gluons interact with quarks and other gluons
    • These types of charge follow different “rules” for behavior than electric charge
  • Importantly, strong interactions behave differently depending on the distance between the two interacting particles
    • The difference between how the storng force mediates binding to neuclons together within an atom vs. binding quarks together within a nucleon
    • Most of the mass (~99%) of a hadron is due to strong force field energy
    • In the range of mediating quark behavior to form a hadron, the force carried by gluons is called “color force” (rather than the more general “strong force”)
    • Hadrons bound by the strong force (larger range) can generate new massive particles because the storng force is so large
      • Thus, if hadrons are struck by high-energy particles, rather than emitting gluons (i.e., freely-moving radiation), they give rise to new hadrons
      • It is actually the residuum of the strong interaction between quarks that make up protons and neutonrs (and other hadrons)
      • In this context (i.e., larger-scale behavior), strong force is often called the nuclear force or residual strong force


  • Most accurately described by the general theory of relativity (Einstein, 1915)
    • Describes gravity as a consequence of the curvature of spacetime (rather than a force) caused by the uneven distribuiton of mass
  • Weakest of the four fundamental interactions/forces
    • No significant influence at the atomic scale **this is important
    • Dominant force at the macroscopic scale instead
  • We still need to come up with a Quantum Gravity Theory that coincides with theories underlying QED, QFD, and QCD

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