P4: The 4 Fundamental Forces
All around us, all interactions can be thought of as the sum of these 4 Forces, but how do they work? What mediates them? How strong are they? Let's explore these ideas further.
What are the 4 Fundamental Forces
The Fundamental Forces are the different forces that mediate all interactions around us. Any interactions, or actions, can be characterized through the different Fundamental Forces.
1. Electromagnetism
Electromagnetism is the most observable of the 4 Fundamental Forces, being responsible for managing the flow of electrical currents, with the motion of these charged particles resulting in the production of Magnetic Fields, like the one around Earth. This Force is mediated by the Photon, which is considered near massless, and was first theorized in 1905, by Albert Einstein, when he wrote a paper regarding the Photoelectric Effect, where light incident on a metal (which was previously thought to be a wave) would only be absorbed as complete units, which helped explain the observations made.
It also allows for Subatomic Particles to exert forces on one another, with their Magnitude and Direction being dependent on the two point-charges which the force acts.
The Formula that dictates the Force experienced on two-point charges is known as Coulomb’s Law and is calculated as:
Here, k represents Coulomb’s Constant, which like all other constants is just substituted in to ensure the correct value for the force, but never changes.
qQ is the product of our two point-charges, which can either be positive or negative. If both charges are the same (Both positive or negative), then this is a repulsive force that pushes the charges apart, whilst if both charges differ (One attractive and one repulsive), then this is an Attractive Force.
If it’s an Attractive Force, it will have a positive value, whilst if it’s a Repulsive Force, there will be a negative value.
d is the distance between our point charges, with this pattern being present in another of the 4 Fundamental Forces, where an increased distance will mean a weaker force between our two point charges.
This equation can be rearranged to show different values, such as Electric Field Strength [E] (Force needed, per unit charge, to move an Electric Charge through an Electric Field).
2. The Strong Nuclear Force
The Nucleus consists of many positively charged particles, which should repel each other, with electrons in Shells around the Nucleus that should be attracted to it, yet the Nucleus is still held together. Why is this?
The answer is the Strong Nuclear Force, which is the strongest of the 4 Fundamental Forces and acts to hold the Nucleus together. The specifics of how it works are very complicated, but in short: Gluons are exchanged between Nucleons, and this interaction is strongest when the Nucleons are at a distance of 1fm (10^15m) from neighboring Nucleons.
If they’re less than 1fm from each other, then the Strong Nuclear Force is repulsive, but if at a distance greater than 1fm, it’s an Attractive Force. It tries to keep Nucleons at this specific distance. At 1fm, the Strong Nuclear Force will have the same Magnitude as the Electromagnetic Repulsion between the Nucleons, specifically Protons.
3. The Weak Nuclear Force
The Weak Nuclear Force is the weakest of the 4 Fundamental Forces and is responsible for causing certain forms of Nuclear Decay.
Nuclear Decay is caused to maintain a balance between the Strong Nuclear Forces in the Nucleus, and the Electromagnetic Forces within the atom, and will typically evolve the emission of certain particles.
More specifically, forms of Radioactive Decay which involve a change in the particle’s identity are mediated by the Weak Nuclear Force.
This is because the Weak Nuclear Force also allows Quarks to change flavors, which in stars allows for Neutrons to transform into Protons, by changing one of the Quark’s flavors from Down to Up (uud) in the process of Beta Minus Decay, which helps with Fusion.
This is the only of the 4 Fundamental Forces, that we know of, that is mediated through 2 different bosons, those being the W and Z Bosons, which have a much higher rest energy/mass than the Gauge Bosons which mediate the other Fundamental Forces. It’s this higher rest mass that makes it the weakest of the Fundamental Forces, as it means these Bosons can’t permeate/travel as far through space.
4. Gravity
Gravity is an attraction, which pulls bodies of mass towards one another. Prior to Einstein’s General Relativity, Gravity was simply thought of as a force acting between two points, or objects, but was then revised to be thought of as being caused by Spacetime’s Curvature around bodies of mass, where a body near a point of greater gravitational influence would experience a slowed passage of time.
The main equation used in determining gravitational forces is Newton’s Law of Gravitation, which can be calculated as:
mM here is the product of our two masses, with an example being the mass of some person and the mass of the Earth, which would mean the Force calculated is the Force of Attraction between the Earth and this person. This force acts in both directions, so just as the Earth pulls us towards it, we pull the Earth towards us, though the immense mass of the Earth means the acceleration experienced is near zero.
d here represents the distance between both bodies of mass, whilst G is Newton’s Gravitational Constant, so just an unchanging value that needs to be substituted each time.
As with Coulomb’s Law, this equation has variations that can be used to calculate other values, such as the Gravitational Field Strength (The strength of the Magnetic Field, or Gravitational Force experienced per unit of Mass → same value as g)
Mediating these Forces
For all these forces, excluding Gravity, we know that they work through the exchange of Bosons between different particles.
Electromagnetism involves the exchange of Photons between particles, with the direction of this force being dependent on their charges.
The Weak Nuclear Force is mediated by 3 individual bosons: The W+ and W- (an Antiparticle Pair, with charges of +1 and -1 respectively), and the Z Boson, which has a relative charge of 0
The Strong Nuclear Force involves the exchange of Gluons.
Gravity is the only of the 4 Fundamental Forces which we have yet to observe being mediated by a Boson, or other subatomic particle.