Science › Fields & particles
The Standard Model
1975· Theory
ProvenTested many times; part of working physics.
The theory of all known particles and three of the four forces, assembled in the 1970s and confirmed by every collider test since.
See it on the Science map →How it works
It lists 17 fundamental particles: six quarks, six leptons (including the electron and three neutrinos), four force carriers (photon, gluon, W and Z) and the Higgs boson. Each is a ripple in a quantum field. The rules of how they interact follow from a few symmetries. About 19 numbers, such as particle masses, must be measured rather than predicted.
Why it matters
It is the most successful theory ever, explaining everything in a lab except gravity. Every particle it predicted has been found.
Think of it like
Like a fully specified building code: it covers every material and connection on site, but not the ground beneath (gravity) or why the code numbers are what they are.
How we know
Predicted particles found on schedule: W and Z (1983), top quark (1995), tau neutrino (2000), Higgs (2012). Precision measurements at CERN and Fermilab agree to many decimal places.
Still a mystery
It omits gravity, dark matter and dark energy, does not predict neutrino masses, and cannot explain why matter beat antimatter.
Connections (11)
▸Quantum field theory is the framework of The Standard ModelProven
The relationship
The Standard Model is a specific quantum field theory: a list of fields, and rules for how they interact set by symmetries. Quantum field theory supplies the grammar; the Standard Model is the particular sentence that describes our universe. Every calculation of a collider result runs on this framework.
How the link was found
Built from 1954, when Chen-Ning Yang and Robert Mills generalized QED's symmetry. Gerard 't Hooft and Martinus Veltman proved in 1971 such theories give finite answers (Nobel 1999).
Why it's proven
Thousands of collider measurements over 50 years agree with Standard Model calculations.
Open questions and mysteries
Quantum field theory may only be an approximation of something deeper that also includes gravity.
▸QED: the theory of light and electrons is one part of The Standard ModelProven
The relationship
QED, the theory of light and electrons, became part of a larger 'electroweak' theory. At everyday energies, electromagnetism and the weak force look separate. At energies above about 100 times a proton's mass, they behave as one. QED is the low-energy face of that combined theory, which is one pillar of the Standard Model.
How the link was found
Sheldon Glashow (1961), Steven Weinberg (1967) and Abdus Salam (1968) built the electroweak theory; Nobel 1979.
Why it's proven
Predicted 'neutral current' interactions were seen at CERN in 1973, and the W and Z particles in 1983, at the predicted masses.
Open questions and mysteries
Why the electroweak force split into two at a particular energy is described, but not deeply explained.
▸The strong force and quarks is one part of The Standard ModelProven
The relationship
Quantum chromodynamics, the theory of quarks and gluons, is the strong-force piece of the Standard Model. It uses the same kind of symmetry-based field theory as the electroweak part but with three types of 'color' charge. Combined with electroweak theory, it covers every particle interaction seen in a lab.
How the link was found
Murray Gell-Mann, Harald Fritzsch and Heinrich Leutwyler (1973), with the key discovery of Gross, Wilczek and Politzer the same year.
Why it's proven
Particle jets at colliders, gluons seen at DESY in 1979, and precise calculations of proton collisions all match.
Open questions and mysteries
The strong and electroweak forces sit side by side but are not truly unified. Grand unified theories that would merge them remain unconfirmed.
▸The weak force and radioactivity is one part of The Standard ModelProven
The relationship
The weak force is described in the Standard Model through the electroweak theory, combined with electromagnetism. Its W and Z carriers are heavy, which is why it is weak at low energies. It is the only part of the model that changes one particle type into another, like a neutron into a proton.
How the link was found
Glashow, Weinberg and Salam, 1961-68. Gerard 't Hooft proved in 1971 the theory gives finite answers.
Why it's proven
W and Z bosons discovered at CERN in 1983 (Nobel 1984 to Carlo Rubbia and Simon van der Meer), with properties since measured very precisely.
Open questions and mysteries
Neutrinos turned out to have mass (1998), which the original model did not include. How they get it is unknown.
▸The Higgs field and boson (2012) completes The Standard ModelProven
The relationship
Without the Higgs field, the W and Z bosons, electrons and quarks would all be massless, and the theory's predictions would break down at high energies, giving probabilities above 100%. The Higgs field fixes both problems. It was the last predicted particle of the Standard Model to be found, completing the set.
How the link was found
Proposed in 1964 by Peter Higgs, by François Englert with Robert Brout, and by Guralnik, Hagen and Kibble. Weinberg built it into the electroweak theory in 1967.
Why it's proven
Found in 2012 at the Large Hadron Collider. Its measured interactions with other particles so far agree with predictions.
Open questions and mysteries
Why the particles' interactions with the Higgs, and so their masses, have the values they do is not explained.
▸Symmetry and group theory is the blueprint of The Standard ModelProven
The relationship
The Standard Model is built by demanding particular local symmetries, called gauge symmetries. Requiring them forces force-carrying particles to exist: the photon for electromagnetism, W and Z for the weak force, gluons for the strong force. The symmetry groups dictate how those forces behave; the Higgs mechanism explains why some symmetry is hidden.
How the link was found
Chen Ning Yang and Robert Mills introduced the approach in 1954; Glashow, Weinberg and Salam built the electroweak theory (1961–1968); the strong-force theory followed in 1973.
Why it's proven
W and Z bosons were found at CERN in 1983, the Higgs boson in 2012, and countless precision tests match predictions.
Open questions and mysteries
Why these particular symmetry groups and not others; why the particles have the masses they do; how gravity fits in.
▸The four forces of nature has three described by The Standard ModelProven
The relationship
The Standard Model describes electromagnetism, the weak force and the strong force in one consistent quantum framework. Electromagnetism and the weak force are truly merged into one electroweak force; the strong force sits alongside under the same rules. Gravity is left out entirely.
How the link was found
Assembled 1961-1975 by Glashow, Weinberg, Salam, Gell-Mann, 't Hooft, Gross, Wilczek, Politzer and many others.
Why it's proven
Every lab-scale experiment involving these three forces matches the model's predictions.
Open questions and mysteries
Why three forces with such different strengths? Whether they fully unify at very high energy, as some theories suggest, is untested.
▸The Standard Model leaves out gravity, so it is not A theory of everythingOpen question
The relationship
The Standard Model covers three forces and all known particles, but it has no place for gravity. Adding gravity using the same methods produces infinite answers that cannot be removed. It also leaves out dark matter and dark energy, and has about 19 numbers it cannot explain. A theory of everything would need to contain it as a special case.
How the link was found
The gravity problem was shown in 1974 by 't Hooft and Veltman and confirmed by Marc Goroff and Augusto Sagnotti in 1986.
Is it proven?
Its gaps are clear: it misses gravity and dark matter. No proposed successor has been confirmed.
Open questions and mysteries
Whether the Standard Model is a low-energy approximation of string theory or something else, nobody knows.
▸The Standard Model cannot explain Dark matterOpen question
The relationship
Dark matter must be stable, heavy enough to clump, and almost invisible to light. No Standard Model particle fits. Neutrinos come closest but are far too light and fast-moving; they would smear out galaxy formation. So if dark matter is a particle, it lies outside the Standard Model, a clear sign the model is incomplete.
How the link was found
Fast neutrinos were ruled out as the main dark matter by structure-formation simulations in the early 1980s.
Is it proven?
Not a proof that new particles exist, but a strong inference. Large Hadron Collider searches and underground detectors such as LZ have found no candidate so far.
Open questions and mysteries
Is dark matter one particle or a whole hidden sector? Could it interact with ordinary matter only through gravity, making it undetectable?
▸Gerard 't Hooft proved the math consistent (Nobel 1999) The Standard ModelProven
The relationship
Early versions of the Standard Model gave infinite, meaningless answers in detailed calculations. 't Hooft proved the infinities could be systematically removed, a property called renormalizability. That turned the electroweak theory from a promising sketch into a precise calculator.
How the link was found
Gerard 't Hooft with his adviser Martinus Veltman at Utrecht, 1971-72. They shared the 1999 Nobel Prize in Physics.
Why it's proven
The theory's precise predictions were confirmed: W and Z particles at CERN in 1983, the top quark's mass before its 1995 discovery, and the Higgs boson in 2012.
Open questions and mysteries
Why the Standard Model's parameters have their values, and how to include gravity, remain open.
▸The Standard Model would need new particles like WIMPs: heavy, shy particlesSpeculative
The relationship
The Standard Model has no particle that is heavy, stable and dark. But theories built to fix a different puzzle, why the Higgs boson is so light, often add one. In supersymmetry, every known particle has a heavier partner, and the lightest partner, in many versions the neutralino, cannot decay. It would be a natural WIMP, at about the mass scale the LHC was built to explore.
How the link was found
Heinz Pagels and Joel Primack (1982) suggested supersymmetric dark matter; Haim Goldberg (1983) and John Ellis and colleagues (1984) singled out the neutralino.
Is it proven?
Not proven. The LHC has found no supersymmetric partners, ruling out those of quarks and gluons up to roughly 1–2 TeV, about 1,000–2,000 proton masses, in simple versions.
Open questions and mysteries
Is supersymmetry absent, or just heavier than the LHC can reach? Without it, the light Higgs and the WIMP lose their shared explanation.