A guide to the visualization
What you are looking at. ✕ Helium-4 is a bound system of two protons and two neutrons, called an alpha particle. Its ground state has total angular momentum zero and positive parity. This explorer uses published nuclear calculations for its density views and explicit diagrams for structure at the quark level.
01 / Constituent diagrams The four nucleon centers, soft envelopes, quark symbols and connecting paths form a moving explanatory layout. Each nucleon changes position independently, and each valence-quark cloud shifts within its parent nucleon. Smooth, irregular rearrangements remove the impression of a rigid assembly. Labels and coupling ribbons follow the moving centers. They are not a measured configuration, hard particle boundaries, a fixed tetrahedral structure or classical orbits. Spreading the diagram only separates the symbols. The motion is an animation of symbols, not nuclear dynamics: neither measured particle tracks nor trajectories from a quantum calculation. Keeping the diagram centered and its labels separated is a visual convention, not a nuclear force law. The Density view separately samples the published stationary one-body distribution.
02 / Published nuclear density The Density and Interactions views use Robert B. Wiringa’s Argonne tables, from 500,000-sample variational Monte Carlo calculations. Choose either the Norfolk chiral EFT interaction NV2+3-Ia or Argonne v18 plus Urbana X. Both include two- and three-nucleon terms. These are model predictions, not an exact solution of QCD or an experimental photograph.
The one-body table describes point-nucleon centers relative to the nuclear center of mass. The supplied isospin-symmetric ⁴He tables use the same spatial distribution for protons and neutrons. Real small charge-symmetry-breaking differences are not resolved here. Linear interpolation and a small normalization correction make each displayed species integrate to two. The chart uses a normalized radial probability density.
P(r) = 4πr²ρ(r) / ∫4πr²ρ(r) dr
Each dot in Density is an independent sample of that one-body marginal, not one of four simultaneously observed nucleons. Dots fade and are resampled without paths. The underlying ground-state density stays stationary; the animation clock is arbitrary. The glow is a tone-mapped line-of-sight integral. It is not an additional physical field.
03 / What three quarks means A proton has valence content uud, a neutron udd. Up and down quarks carry electric charges +⅔e and −⅓e. Thus the nucleus has six net up and six net down valence quarks. This does not mean there are exactly twelve quarks in the full quantum state: gluons and sea quark–antiquark contributions are essential, and parton distributions depend on the probing scale.
The colored symbols show a representative color basis. The nucleon is a color singlet, not three permanent colored balls. Gluons carry color charge and couple to each other as well as to quarks. Reshaping light patches, flexing ribbons and renewing sea symbols make the diagram visibly active. Changing RGB hues emphasize that no valence quark has a permanent color assignment; these blends are illustrative, not computed color-state probabilities. None of these patterns calculates a gauge-field strength, quark probability density, physical lifetime or parton trajectory. The speed slider controls the illustration only. In the ground state, expectation values of time-independent observables are stationary.
|color⟩ = (rgb − rbg + gbr − grb + brg − bgr) / √6
04 / Binding and correlations The residual strong interaction binds color-singlet nucleons. Its long-range part can be described by pion exchange; nuclear interactions also contain shorter-range, spin, isospin, tensor and many-body terms. The golden links symbolize coupling, not permanent bonds or freely traveling gluons between nucleons. Repulsive electromagnetic interactions act between protons.
The pair chart displays a probability of separation, not a force or a potential. Each pair curve is divided by its pair count and normalized: one pp, one nn and four np pairs. The same supplied curve is used for pp and nn. Short-distance behavior depends on the nuclear interaction model. Probing r does not move the quantum state. The pair diagram changes orientation while preserving the selected three-dimensional separation. The pp Coulomb readout is the point-charge estimate 1.43996448/r MeV; at overlapping separations the finite extent of nucleons matters.
B = (2mₚ + 2mₙ − mα)c² ≈ 28.296 MeV
The binding energy is the energy needed to separate this nucleus into free nucleons. It is not obtained by adding the diagram’s links. The measured RMS charge radius, 1.6785(21) fm, includes internal charge structure and is not the RMS radius of the point-nucleon centers.
Sources & data Version 3 · All tables and drawing code are embedded in this HTML. The app works offline. No external scripts or fonts are required. Reduced-motion preferences pause the animation initially.
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