Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo

Key Terms

subatomic particle with the same mass and lifetime as its associated particle, but opposite electric charge
baryon number
baryon number has the value B=+1B=+1 for baryons, 11 for antibaryons, and 0 for all other particles and is conserved in particle interactions
group of three quarks
Big Bang
rapid expansion of space that marked the beginning of the universe
particle with integral spin that are symmetric on exchange
property of particles and that plays the same role in strong nuclear interactions as electric charge does in electromagnetic interactions
cosmic microwave background radiation (CMBR)
thermal radiation produced by the Big Bang event
study of the origin, evolution, and ultimate fate of the universe
dark energy
form of energy believed to be responsible for the observed acceleration of the universe
dark matter
matter in the universe that does not interact with other particles but that can be inferred by deflection of distance star light
electroweak force
unification of electromagnetic force and weak-nuclear force interactions
exchange symmetry
property of a system of indistinguishable particles that requires the exchange of any two particles to be unobservable
particle with half-integral spin that is antisymmetric on exchange
Feynman diagram
space-time diagram that describes how particles move and interact
fundamental force
one of four forces that act between bodies of matter: the strong nuclear, electromagnetic, weak nuclear, and gravitational forces
particle that that carry the strong nuclear force between quarks within an atomic nucleus
grand unified theory
theory of particle interactions that unifies the strong nuclear, electromagnetic, and weak nuclear forces
a meson or baryon
Hubble’s constant
constant that relates speed and distance in Hubble’s law
Hubble’s law
relationship between the speed and distance of stars and galaxies
a fermion that participates in the electroweak force
lepton number
electron-lepton number Le,Le, the muon-lepton number Lμ,Lμ, and the tau-lepton number LτLτ are conserved separately in every particle interaction
a group of two quarks
creation of heavy elements, occurring during the Big Bang
particle accelerator
machine designed to accelerate charged particles; this acceleration is usually achieved with strong electric fields, magnetic fields, or both
particle detector
detector designed to accurately measure the outcome of collisions created by a particle accelerator; particle detectors are hermetic and multipurpose
quantum chromodynamics (QCD)
theory that describes strong interactions between quarks
quantum electrodynamics (QED)
theory that describes the interaction of electrons with photons
a fermion that participates in the electroweak and strong nuclear force
lengthening of the wavelength of light (or reddening) due to cosmological expansion
Standard Model
model of particle interactions that contains the electroweak theory and quantum chromodynamics (QCD)
particle property associated with the presence of a strange quark
strong nuclear force
relatively strong attractive force that acts over short distances (about 10−1510−15 m) responsible for binding protons and neutrons together in atomic nuclei
circular accelerator that uses alternating voltage and increasing magnetic field strengths to accelerate particles to higher and higher energies
synchrotron radiation
high-energy radiation produced in a synchrotron accelerator by the circular motion of a charged beam
theory of everything
a theory of particle interactions that unifies all four fundamental forces
virtual particle
particle that exists for too short of time to be observable
W and Z boson
particle with a relatively large mass that carries the weak nuclear force between leptons and quarks
weak nuclear force
relative weak force (about 10−610−6 the strength of the strong nuclear force) responsible for decays of elementary particles and neutrino interactions
Order a print copy

As an Amazon Associate we earn from qualifying purchases.


This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at
Citation information

© Jan 19, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.