Science, Tech, Math › Science The 4 Fundamental Forces of Physics Share Flipboard Email Print This Hubble Space Telescope view reveals thousands of galaxies stretching back into time across billions of light-years of space. The image covers a portion of a large galaxy census called the Great Observatories Origins Deep Survey (GOODS). NASA, ESA, the GOODS Team, and M. Giavialisco (University of Massachusetts, Amherst) Science Physics Physics Laws, Concepts, and Principles Quantum Physics Important Physicists Thermodynamics Cosmology & Astrophysics Chemistry Biology Geology Astronomy Weather & Climate By Andrew Zimmerman Jones Math and Physics Expert M.S., Mathematics Education, Indiana University B.A., Physics, Wabash College Andrew Zimmerman Jones is a science writer, educator, and researcher. He is the co-author of "String Theory for Dummies." our editorial process Andrew Zimmerman Jones Updated January 19, 2019 The fundamental forces (or fundamental interactions) of physics are the ways that individual particles interact with each other. It turns out that every single interaction observed taking place in the universe can be broken down and described by only four (well, generally four—more on that later) types of interactions: GravityElectromagnetismWeak Interaction (or Weak Nuclear Force)Strong Interaction (or Strong Nuclear Force) Gravity Of the fundamental forces, gravity has the farthest reach, but it's the weakest in actual magnitude. It is a purely attractive force which reaches through even the "empty" void of space to draw two masses toward each other. It keeps the planets in orbit around the sun and the moon in orbit around the Earth. Gravitation is described under the theory of general relativity, which defines it as the curvature of spacetime around an object of mass. This curvature, in turn, creates a situation where the path of least energy is toward the other object of mass. Electromagnetism Electromagnetism is the interaction of particles with an electrical charge. Charged particles at rest interact through electrostatic forces, while in motion they interact through both electrical and magnetic forces. For a long time, the electric and magnetic forces were considered to be different forces, but they were finally unified by James Clerk Maxwell in 1864, under Maxwell's equations. In the 1940s, quantum electrodynamics consolidated electromagnetism with quantum physics. Electromagnetism is perhaps the most prevalent force in our world, as it can affect things at a reasonable distance and with a fair amount of force. Weak Interaction The weak interaction is a very powerful force that acts on the scale of the atomic nucleus. It causes phenomena such as beta decay. It has been consolidated with electromagnetism as a single interaction called the "electroweak interaction." The weak interaction is mediated by the W boson (there are two types, the W+ and W- bosons) and also the Z boson. Strong Interaction The strongest of the forces is the aptly-named strong interaction, which is the force that, among other things, keeps nucleons (protons and neutrons) bound together. In the helium atom, for example, it is strong enough to bind two protons together even though their positive electrical charges cause them to repulse each other. In essence, the strong interaction allows particles called gluons to bind together quarks to create the nucleons in the first place. Gluons can also interact with other gluons, which gives the strong interaction a theoretically infinite distance, although it's major manifestations are all at the subatomic level. Unifying the Fundamental Forces Many physicists believe that all four of the fundamental forces are, in fact, the manifestations of a single underlying (or unified) force which has yet to be discovered. Just as electricity, magnetism, and the weak force were unified into the electroweak interaction, they work to unify all of the fundamental forces. The current quantum mechanical interpretation of these forces is that the particles do not interact directly, but rather manifest virtual particles that mediate the actual interactions. All of the forces except for gravity have been consolidated into this "Standard Model" of interaction. The effort to unify gravity with the other three fundamental forces is called quantum gravity. It postulates the existence of a virtual particle called the graviton, which would be the mediating element in gravity interactions. To date, gravitons have not been detected, and no theories of quantum gravity have been successful or universally adopted.