Bosons are particles that carry energy and forces throughout the universe.
The Standard Model of particle physics—the most robust theory we have about the subatomic world—divides every particle into the universe and even the larger composite particles fit into two broad categories; fermions and bosons.
Fermions such as quarks, electronsneutrinos, protons and neutrons are the basis of matter, while a category of bosons, the gauge bosons, are responsible for acting as ‘carriers’ of at least three of the four basic forces— electromagnetism, the strong nuclear force and the weak nuclear force. This means that fermions interact with each other via the exchange of gauge bosons.
There may also be a boson to carry the force gravity , but it is not certain at the moment. The gauge bosons are fundamental particles – meaning they are not made up of smaller particles – but there are other bosons that are made up of smaller particles.
Related: The Higgs Boson: The ‘God Particle’ Explained
Robert Lea has a bachelor’s degree in physics and astronomy from the UK’s Open University. Robert has contributed to Space.com for over a decade, and his work has appeared in Physics World, New Scientist, Astronomy Magazine, All About Space, and more.
Bosons: What makes a particle a boson?
Bosons take their name from the Indian physicist Satyendra Nath Bose, who conducted important research in the 1920s regarding the behavior of the most famous boson – the photon.
One of the most important defining properties of bosons relates to a quantum mechanical quality called ‘spin’, which can be thought of as the deflection a particle takes when it experiences a magnetic field that imparts angular momentum.
Although similar, spin is more complex than angular momentum in the macroscopic world of classical physics, mainly because particles can have fractions of spin, which means there is no real “classical” way to describe spin.
A fermion is a particle with 1/2 spin that can have plus or minus values. This means that fermions can have values like 1/2, -1/2, 3/2 and -3/2. Plus or minus determines the direction of the intrinsic angular momentum particle will take.
Bosons, on the other hand, have whole integer spins including zero. This means that the spin values that these particles can take are 0, 1, -1, 2, -2 and so on.
Mathematically, adding two halves together makes a whole integer, and similarly, a combination of even numbers of fermions creates a larger particle that is a boson.
These include mesons – which are formed when two quarks bind – and even atoms with even numbers of fermions. For example, helium-4 atoms are bosons because they consist of two protons, two neutrons, and two electrons. Helium-4 atoms will have particular relevance when considering the special and unique properties of bosons.
What are the different bosons?
Bosons can be divided in a few ways, but to introduce the various particles that make up this wing of the ‘particle zoo’ it is convenient to sort them into two broad groupings – particles for which we have experimental evidence and those that are currently only theoretical.
The most famous gauge boson is easily the photon, the particle of light and the mediator of the electromagnetic force.
For photons—which have a spin of 1—spin is the quantum mechanical equivalent of polarization, or the direction a light wave is oriented in. This means that photon spins can be parallel or antiparallel in orientation.
Photons were the first gauge bosons to be discovered when Max Planck and Max Planck in the early 20th century. Albert Einstein proposed light exists in packets of energy called ‘quanta’. The name ‘photon’ was introduced for these quanta in 1928 by the American chemist Gilbert Lewis.
Related: The double-slit experiment: Is light a wave or a particle?
(opens in new tab)
Gluons, the second gauge boson discovered, are the bosons that carry the strong nuclear force. As a result, they are responsible for ‘gluing’ other particles together.
Specifically, gluons bind quarks together to create protons and neutrons. But gluons don’t stop there: They also bind these composite particles – collectively called ‘nucleons’ – together in the atomic nucleus at the heart of all everyday matter.
Gluons were discovered at the electron-positron collider PETRA in DESY, Germany, in 1979.
The W and Z bosons
The W and Z bosons are the gauge bosons responsible for carrying the weak nuclear force – stronger than gravity, but only effective over incredibly short distances. These spin 0 bosons are responsible for nuclear decay, where one element changes into another by helping protons change to neutrons and vice versa.
One of the big problems with the W and Z bosons, discovered in 1983, was figuring out how they got their mass, since theories at the time suggested they should be massless like the photon.
That Higgs boson was first introduced into the Standard Model of particle physics to explain how the W and Z bosons got their mass, but its mass-giving role as a facilitator of the Higgs field was soon extended to almost all particles.
The Higgs boson was discovered in 2012 by arising from high-energy proton-proton collisions at Large Hadron Collider(LHC) — the world’s most powerful particle accelerator.
The Higgs boson has a proposed spin of 0, and its discovery is said to have completed the Standard Model, but there is still physics outside of this model to discover. The exploration of physics beyond the Standard Model means there are other theoretical bosons to explore.
(opens in new tab)
One thing that the framework of the Standard Model of particle physics cannot describe is gravity. That’s because quantum mechanics – the physics of the subatomic – and general relativityEinstein’s theory of gravity must not be masked.
The other fundamental forces get a gauge boson to carry them (and the weak force even gets two), so why shouldn’t gravity? A gauge boson for gravity—the “graviton”—has been theorized but has so far failed to manifest experimentally.
Because gravity is negligible at a subatomic level, missing gravitons and the lack of a ‘quantum theory of gravity’ have not hindered this model too much.
A potential model of physics beyond the standard model is ‘supersymmetry’. This theory – proposed to ‘fix’ the mass of the Higgs boson – suggests that every fermion in the particle zoo has a bosonic partner.
The extra particles would help ‘offset’ some of the mass of the Higgs boson, which explains why it is relatively light.
Bosons: The ‘social’ particles
Thanks to a phenomenon called the Pauli exclusion principle, half-integer spin fermions are unable to possess the same quantum numbers. This means that fermions are unable to cluster together.
However, bosons do not obey the Pauli exclusion principle with their full integer spins. This means they can cluster closely together, giving rise to some unique physical properties.
The most common example of ‘social bosons’ is laser light, which consists of photons of the same wavelength and frequency, all traveling in the same direction.
(opens in new tab)
A more exotic example of bosons defying the Pauli exclusion principle was proposed in 1924. Albert Einstein and Bose determined that bosons should condense together in their ground state—the state of their lowest possible energy—leading to Bose-Einstein condensation, the creation of superfluidity in liquid helium cooled to 2.17 K and thus its lowest possible energy.
Paired electrons – called ‘Cooper pairs’ – are classified as ‘quasi-particles’ and can be forced to behave like bosons and condense into a state with zero electrical resistance. The creation of Bose-Einstein condensation in dilute gases of alkali atoms would win three scientists the Nobel Prize in Physics in 2001 (opens in new tab).
Explore the Higgs boson in more detail and discover why it is so special with CERN (opens in new tab).
Learn more about particle physics with this free course from The Open University (opens in new tab).
“Fermions, Bosons (opens in new tab).” Hyperphysics (2022).
“The standard model (opens in new tab).” CERN (2022).
“Meet a super partner at the LHC (opens in new tab).” APS Physics (2010).
“Supersymmetry (opens in new tab).” CERN (2022).
“The Discovery of the Gluon (opens in new tab).” Sau Lan Wu, University of Wisconsin-Madison/CERN,(2018).
“This Month in Physics History (opens in new tab).” APS News (2012).
Follow us on Twitter @Spacedotcom (opens in new tab) or on Facebook (opens in new tab).