The Standard Model is the quantum theory that describes known elementary particles and the electromagnetic, weak and strong interactions among them, but it does not include a quantum description of gravity.
The particles of matter
The Standard Model groups matter particles into quarks and leptons arranged in three generations. Up and down quarks make protons and neutrons; electrons are leptons. The heavier generations have similar interaction patterns but are unstable and decay into lighter particles.
Each matter particle also has an antiparticle with corresponding mass and opposite quantum numbers such as electric charge where applicable.
Particles that carry interactions
Photons mediate the electromagnetic interaction, gluons carry the strong interaction, and W and Z bosons mediate the weak interaction. The theory describes these forces through quantum fields and symmetries.
Gravity is one of the four fundamental interactions but is not included in the Standard Model. At everyday and astrophysical scales it is described extremely well by general relativity.
The Higgs field and particle masses
The Standard Model includes the Higgs field, whose interaction with elementary particles helps determine their masses. The associated Higgs boson was discovered at CERN in 2012, confirming a central part of the mechanism.
Most of the mass of ordinary protons and neutrons, however, comes from the energy of the strong interaction binding quarks and gluons rather than directly from the Higgs field.
What the Standard Model cannot explain
The framework does not identify the nature of dark matter or dark energy, explain why the universe contains much more matter than antimatter, or provide a quantum theory of gravity. Neutrino masses also require extensions beyond the model’s simplest original form.
These gaps are why physicists continue precision measurements and searches for new particles and interactions.
