Working drawings for the smallest things. The Standard Model is the most precisely tested theory in human history — and it is incomplete.
Twelve fermions, four gauge bosons, one Higgs scalar. SU(3)C × SU(2)L × U(1)Y. Constructed piece by piece from the 1950s through the 1970s; verified, decimal by decimal, ever since.
FIG. 01 · STANDARD MODEL — THREE GENERATIONS, FOUR FORCES, ONE HIGGS
Mediator: 8 gluons. Range: ~1 fm. Coupling αs ≈ 0.118 at MZ. Confines quarks; binds protons and neutrons via residual force.
Mediator: photon (massless). Infinite range. Coupling α ≈ 1/137. Holds atoms together; carries light, chemistry, electricity.
Mediator: W±, Z0. Range: ~10⁻¹⁸ m. Drives β-decay, neutrino interactions, hydrogen → helium fusion in the Sun.
Hypothetical graviton (spin-2). Infinite range. ~10⁴⁰× weaker than EM. Quantum description: still missing.
The Standard Model Lagrangian, schematically:
Term by term:
Spontaneous symmetry breaking → mass
1964: Peter Higgs, François Englert, Robert Brout, and others propose a scalar field whose nonzero vacuum expectation value gives mass to the W and Z bosons (and, via Yukawa coupling, to fermions). The photon stays massless.
2012: ATLAS and CMS at the LHC announce a 125 GeV scalar — the Higgs boson — at 5σ. Higgs and Englert share the 2013 Nobel.
Without it, electroweak symmetry would be unbroken, electrons would be massless, atoms would not exist, and you would not be reading this.
Branching ratios at mH = 125 GeV
Richard Feynman, 1949. Time runs left to right. Straight lines: fermions (arrows show particle direction). Wavy: photons. Curly: gluons. Dashed: scalars. Each vertex carries a coupling constant.
To probe distance d, you need wavelength < d; for matter waves, that means momentum > ħ/d. To resolve 10⁻¹⁹ m you need TeV scales. Hence the LHC.
CERN's Large Hadron Collider is a 26.7 km synchrotron under the Franco–Swiss border. Two counter-rotating proton beams collide at 13.6 TeV in the ATLAS, CMS, ALICE, and LHCb detectors.
Cathode rays are particles ~2,000× lighter than the proton. The electron.
Gold-foil scattering: atoms have tiny dense nuclei.
Relativistic equation for the electron predicts antimatter. Confirmed by Anderson's positron, 1932.
Neutrino postulated to save β-decay's energy budget. Detected 1956 by Cowan & Reines.
π-meson found in cosmic rays — Yukawa's predicted strong-force carrier.
Quarks proposed to organize the hadron zoo. Confirmed by SLAC deep-inelastic scattering, 1968.
Glashow–Iliopoulos–Maiani; asymptotic freedom (Gross, Politzer, Wilczek — Nobel 2004).
W and Z bosons observed at CERN's SppS — Rubbia and van der Meer Nobel.
Top quark confirmed at Fermilab — last quark of generation 3.
Atmospheric neutrino oscillations — neutrinos have mass.
Higgs boson, m = 125 GeV.
Combined aμ tension with theory: 4.2σ. New physics or hadronic uncertainty?
Concentric layers — silicon trackers, electromagnetic and hadronic calorimeters, muon chambers. A single bunch crossing yields ~30 pile-up vertices; reconstruction software disentangles them in real time.
1867–1934. Discovered radium, polonium; only person with Nobels in two sciences.
1902–84. Relativistic QM, antimatter, magnetic monopoles. Famously laconic.
1918–88. QED, path integrals, diagrams, bongos. Nobel 1965.
1912–97. Co-found parity violation in β-decay, 1956.
1929–2019. Strangeness, the Eightfold Way, quarks. Nobel 1969.
b. 1951. M-theory unification, Fields Medal 1990.
1929–2024. Predicted scalar boson, 1964. Nobel 2013.
b. 1960. ATLAS spokesperson during Higgs discovery; CERN DG since 2016.
Neutral, almost massless, near-light-speed. Each second, ~6.5 × 10¹⁰ solar neutrinos cross every cm² of you. Almost all pass through unhindered.
They oscillate between flavors (e, μ, τ) — observed by SNO and Super-K, Nobel 2015. This requires nonzero mass; sums of mass eigenstates < 0.12 eV from cosmology.
|να⟩ = Σ Uαi |νi⟩
Open: are they Majorana (their own antiparticles)? Is there CP violation in their mixing? Both could explain the cosmic matter–antimatter asymmetry.
Sinusoidal flavor mixing
5× more than baryonic matter. Not in the SM. Candidates: WIMPs, axions, sterile νs, primordial black holes, dark photons.
SM has them strictly massless. Seesaw mechanisms add right-handed Majorana νR at high scale.
Why mH = 125 GeV ≪ MPl = 1.2 × 10¹⁹ GeV? Quantum corrections should push it up. SUSY? Compositeness?
QCD allows CP violation θ̄ ≤ 10⁻¹⁰. Why so small? Peccei–Quinn symmetry → axion.
Sakharov conditions: B-violation, C/CP-violation, departure from equilibrium. SM CP-violation insufficient.
No renormalizable QFT for spin-2 gravity. Strings. Loop quantum gravity. Asymptotic safety.
"The first principle is that you must not fool yourself — and you are the easiest person to fool."
Supersymmetry posits a partner for every SM particle differing in spin by ½: squarks for quarks, sleptons for leptons, gauginos for gauge bosons. Elegantly cancels the quadratic divergences in the Higgs mass. Predicts a stable lightest supersymmetric particle — a natural dark matter candidate.
After 13 years of LHC data, no superpartners have been found below ~2 TeV. The minimal scenarios are excluded; less natural ones remain alive but bruised.
Three approaches knock heads against quantum gravity:
Coupling constants α1, α2, α3 nearly meet at ~10¹⁶ GeV under SUSY running — hint at a Grand Unified Theory.
2030 onwards. ×10 luminosity. Higgs self-coupling, rare decays, precision electroweak.
100 km tunnel under Geneva, e⁺e⁻ then 100 TeV pp. Decision pending; commissioning ~2045.
3–10 TeV in compact ring; muons radiate less synchrotron — but hard to cool. R&D underway.
Long-baseline neutrino oscillations; CP violation in lepton sector; proton decay.
Multi-tonne liquid xenon, kilometres deep. WIMP cross-sections under 10⁻⁴⁸ cm².
Resonant cavities sweep μeV–meV axion masses. Could find dark matter this decade.
Plus Veritasium "Why this Higgs result is so important" — and Fermilab's Don Lincoln channel for unfiltered detail.
Drawing reviewed for accuracy as of 2026.05. Standard Model is provisional pending discovery of new physics at higher scales.