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Grand Unified Theory: The Four Fundamental Forces


Justin Gallagher

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While I visited the Rochester Institute of technology over the break, I talked to a Junior who was majoring in Physics. He was explaining to me what he was working on and theorized. He was currently working on the Grand Unified Theory. This interested me quite a bit so I did some research into this subject.

It all starts with the Fundamental forces and their Interactions.

There are 4 fundamental forces that have been identified. In our present Universe they have rather different properties.

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Properties of the Fundamental Forces:


  1. The Strong Nuclear Force is very strong, but very short-ranged. It acts only over ranges of order 10-13 centimeters and is responsible for holding the nuclei of atoms together. Since the protons and neutrons which make up the nucleus are themselves considered to be made up of quarks, and the quarks are considered to be held together by the color force, the strong force between nucleons may be considered to be a residual color force. In the standard model, therefore, the basic exchange particle is the gluon which mediates the forces between quarks. Since the individual gluons and quarks are contained within the proton or neutron, the masses attributed to them cannot be used in the range relationship to predict the range of the force. When something is viewed as emerging from a proton or neutron, then it must be at least a quark-antiquark pair, so it is then plausible that the pion as the lightest meson should serve as a predictor of the maximum range of the strong force between nucleons.



  2. The Electromagnetic Force manifests itself through the forces between charges (Coulomb's Law) and the magnetic force, both of which are summarized in the Lorentz force law. Fundamentally, both magnetic and electric forces are manifestations of an exchange force involving the exchange of photons . The electromagnetic force holds atoms and molecules together. In fact, the forces of electric attraction and repulsion of electric charges are so dominant over the other three fundamental forces that they can be considered to be negligible as determiners of atomic and molecular structure. Even magnetic effects are usually apparent only at high resolutions, and as small corrections.


  3. The Role of the Weak Nuclear Force in the transmutation of quarks makes it the interaction involved in many decays of nuclear particles which require a change of a quark from one flavor to another. It was in radioactive decay such as beta decay that the existence of the weak interaction was first revealed. The weak interaction is the only process in which a quark can change to another quark, or a lepton to another lepton - the so-called "flavor changes".



  4. The Gravitational Force is weak, but very long ranged. It is by far the weakest of the four interactions. The weakness of gravity can easily be demonstrated by suspending a pin using a simple magnet (such as a refrigerator magnet). The magnet is able to hold the pin against the gravitational pull of the entire Earth. Yet gravitation is very important for macroscopic objects and over macroscopic distances. It is the only interaction that acts on all particles having mass; it has an infinite range, like electromagnetism but unlike strong and weak interaction; it cannot be absorbed, transformed, or shielded against and it always attracts and never repels.

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