Physics Ontology

One map of physics, three ways in. Drill down on any quantity to see its units, the equations it lives in, and how its values span the universe.

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σ\sigma
Quantum

Cross Section

Effective area quantifying interaction probability.

SI unit

square metre (m²)

Dimension: [ L2 ][\,L^2\,]

Other units

  • square metre (m²)
  • barn (b)×1.00e-28

Order of magnitude

How values of cross section span the physical world (in m², log scale).

Neutrino scattering
10-47 m²
Nuclear reaction
10-28 m²
Lower limit10-48 m²Upper limit10-24 m²