The standard model of matter
  • The standard model of matter is an attempt to achieve a unified theory of matter.
  • It theorises that all matter and force is composed of small elementary sub atomic particles, and is the result of all evidence we have gathered.
  • The subatomic particles are split into three groups as shown.


Particle Name Symbol Electric charge
Up u $+\frac{2}{3}$
Down d $-\frac{1}{3}$
Charm c $+\frac{2}{3}$
Strange s $-\frac{1}{3}$
Top t $+\frac{2}{3}$
Bottom b $-\frac{1}{3}$
  • Quarks are point-like, fundamental particles with a spin of $\frac{1}{2}$
  • They also each have an anti-matter match-ups with exact opposite properties.
    • For example, an anti-up quark would have a charge of $-\frac{2}/{3}$
  • They are almost never by themselves, as they are affected by the strong force.
  • Each quark has a spin of $\frac{1}{2}$
  • This is mediated by a theory known as Quantum Chromodynamics
    • Each quark has something known as a colour charge.
    • There are three charges for matter: red, green and blue and three charge for antimatter: anti-red, anti-green, and anti-blue
    • Quarks form products when a "white" colour charge is achieved.
      • This is either a "red+green+blue" trio or a "colour+anticolour" pair.
  • The products of quarks are known as Hadrons, and can be split into two major groups:
  • Baryons: These are particles made of 3 quarks
    • This is the "red+green+blue" combo
    • Most notable ones are:
      • Protons (uud)
      • Neutrons (udd)
    • They have half-integer spin, as they are made of 3 quarks.
      • Thus they are qualified as fermions, and obey Pauli's exclusion principle
  • Mesons: These are made of two quarks.
    • Notable mesons are pions (anti-up+down), which mediate the strong nuclear force.
    • As it is a mixture of matter and anti-matter, they decay almost instantaneously.
    • They have integer or zero spin, and are treated like Bosons. Thus, they don't obey Pauli's exclusion principle.


Particle Name Symbol Electric charge
Electron $e^{-}$ -1
Electron neutrino $v_{e}$ 0
Muon $\mu^{-}$ -1
Muon neutrino $v_{\mu}$ 0
Tau $\tau^{-}$ -1
Tau neutrino $v_{\tau}$ 0
  • Leptons are fundamental particles that don't experience the strong force
  • They have very little to no mass
  • They are often the remnants from nuclear decay.
  • Muons and Tau leptons often quickly decay into electrons with a neutrino and an antineutrino


  • Force between particles, according to the standard model, is caused by the exchange of Bosons.
  • There are four basic forces: Strong, Weak, Electromagnetic and Gravity
Force Relative Strength Range (m) Force Carrier
Strong 1 $10^{-15}$ Gluons
Electromagnetic $\frac{1}{137}$ $infinite$ Photon
Weak $10^{-5}$ $10^{-17}$ W and Z Bosons
Gravity $6 \times 10^{-39}$ $infinite$ Graviton? (Yet to be discovered)
  • Strong: This is the force that keeps quarks together.
    • It is extremely strong, and almost always manages to prevent quarks from existing by themselves
    • Its force carrier, the gluon, mediates the colour charge of quarks.
    • Interestingly, the gluon itself has a colour charge.
  • Electromagnetic: This is the simple electromagnetic forces on charged or magnetised objects.
    • The force carrier is the photon, which we know travels at light speed.
    • Quantum Electrodynamics, a subset of this study, suggests that like charges repel as they "sense" each other through exchange of photons.
  • Weak: This is the force that mediates nuclear decay and other changes in colour charge
    • When decay occurs, the particle decays into a W/Z boson, and immediately decays again into the proper particles
    • For this reason, W/Z bosons are extremely large compared to other force carriers.
    • It has been discovered that, at very very small distances ($10^{-17}m$) the electromagnetic force and the weak force have comparable strengths.
    • Thus, they have concluded that the electromagnetic force and the weak force are related in a theory known as Electroweak.
  • Gravity: This is the force that attracts two particles with mass together.
    • Currently, it is not known whether Gravity fits with the standard model as no Graviton has ever been observed.

Pros and cons.


  • Explained the composition of subatomic particles
  • Explained how forces were mediated
  • Named all of the subatomic particles
  • Explained interactions of subatomic particles
  • Predicted existence of some particles
  • Able to link several theories such as Quantum Chromodynamics, Quantum Electrodynamics and Electroweak theory.


  • Incompatible with General Relativity
  • Cannot explain number of particles
  • Cannot generate mechanism for the observed mass of particles (Mass of proton > Mass of its quarks)