The Four Forces
The Strong Nuclear Force
The Weak Nuclear Force
- Alpha radiation is two protons and two neutrons (helium nuclei) ejected from the nucleus of an atom. An example of alpha radiation is uranium decaying into thorium. Alpha particles can be stopped by a piece of paper or a person's skin.
- Beta radiation are electrons or positrons that are emitted as a result of neutrons transforming themselves into protons (strontium-90). The chart at the left depicts the beta decay of a neutron into a proton and emitting an electron and an anti-neutrino mediated (enabled) by the W boson. (See bosons in Force Carriers section below.) A sheet of aluminium can stop beta radiation.
- Gamma radiation consists of very high energy electro-magnetic waves that are the result of the decay of atomic nuclei. There are some naturally occurring gamma decay sources on earth such as potassium-40. Gamma rays are primarily produced by cosmic ray interactions with our atmosphere and also by astronomical events such as supernova explosions. Thick pieces of lead are necessary to stop gamma radiation. Gamma radiation is the most dangerous kind to humans, but we are graciously protected by our upper atmosphere.
Fundamental Particle Decay
- Gluons, the strong force carriers, are responsible for quarks “sticking” together to form protons and neutrons. However, their range is extremely small, just covering the nucleus of atoms. Their force is the strongest as it has to overcome the repulsive forces of the electro-magnetic elements that they "glue" together, mainly protons.
- Photons, the electro-magnetic carriers, bind negative electrons to positive atomic nuclei to form atoms. The electro-magnetic range is infinite and quite strong, but it decreases with distance.
- Bosons, the weak force carriers (W+, W-, and Z) facilitate the decay of heavy particles into lighter particles. Their range is limited to the nucleus just like Gluons. As their name implies, they are not a strong force. The Higgs boson is a major part of the Standard Model, which has just recently been observed. See the section on Standard Model issues below.
- Gravitons, the gravitational force carriers, act between massive objects. Although they play no role at the microscopic level, they are the dominant force at the macro level (in the universe). Their range is infinite but their force is extremely weak unless one is discussing massive objects like the earth or the sun. Gravitons have only been hypothesized, have yet to be observed, and are not supported by the math of Quantum Mechanics. See the section on Standard Model issues below.
The Standard Model
Quantum Mechanics/Standard Model Issues
Although the Standard Model has been exceptionally successful in explaining all experimental phenomena, it is not expected to be the ultimate theory because of its great complexity and the many questions it leaves unanswered. Quantum Mechanics and The Standard Model do provide the best theory we now have of the sub-atomic world, but they do not encompass all the known observations. Here are some of the current issues with quantum theory:
- Although the Standard Model incorporates three of the four fundamental forces, there are no mathematical equations that derive or explain gravity and General Relativity. This is probably the biggest short coming of Quantum Mechanics. Physicists would love to incorporate gravity into The Standard Model, but at this point after many years of trying it seems a long shot.
- Critics consider it to be "inelegant" and arbitrary that 19 numerical constants have to be incorporated into The Standard Model and numerous fields have to be specified beforehand. Also, there is experimental evidence that neutrinos have mass, which The Standard Model does not currently suggest. Neutrinos with mass will require at least 7 additional constants which are also arbitrary. There are just "too many" arbitrary constants required for the theory to be the "final" theory. In the "final" theory, physicists believe the critical constants will come from the theory itself.
- The Standard Model cannot explain the observed amount of "cold dark matter" (21%) in the universe and also its calculations of "dark energy" in the universe are far too large (observed dark energy is 75%) . Only 4% of the universe is "normal" matter, i.e. quarks and leptons.
- It is difficult to accommodate into The Standard Model. the observed predominance of matter over anti-matter resulting from the big bang.
- In order to accommodate the big bang's "inflationary mechanism", The Standard Model will require a major upgrade.
- There are also several other discrepancies that have been observed that conflict with The Standard Model (CP violation, lepton count violation, etc.).
The Four Forces – The Solutions
Gravity, Electromagnetism, the Strong Force and the Weak Force – is it possible to define them and, in doing so, unify them?