Protons contain countless gluons and virtual quark-antiquark pairs at any given time, though they are modeled as composed of just three quarks.

Models of the extreme pressures and energies in neutron stars suggest conditions resembling those believed to have existed within a fraction of a second after the Big Bang. In these environments, the quarks that make up protons and neutrons in trios may instead form pairs that combine to form one quantum object.

One of humanity’s eternal questions surrounds what we are fundamentally made of. Many ancient philosophies believed in a set of classical elements: from water, air, fire and earth of ancient Greeks; to…

The thought experiment explains why every electron has the same charge and mass as every other electron, and describes every positron—the antimatter version of the electron—as that same electron traveling backwards in time. Among other foundational challenges, the model suggests that the universe contains equal numbers of electrons and positrons, yet normal matter is much more common than antimatter.

The mathematics of quantum field theory suggested that force particles should be massless, like the photon for electromagnetism, but the weak nuclear force’s equivalent W and Z particles are not. The Higgs field provides mass when interacting with such particles.

During the proton-proton chain, four hydrogen nuclei—protons—are fused together to create an alpha particle—a helium nucleus—and produce the energy that supports a star's own weight. Through radioactive decay, two of these protons become neutrons, with each releasing an antielectron, or positron, and an electron neutrino.

Using the framework of quantum field theory, it structures all known particles into 12 matter particles, alongside five particles that carry three of the four fundamental forces. Although remarkably precise and predictive, it cannot yet explain gravity, dark matter, or dark energy.

While the strong nuclear force holds the protons and neutrons together in an atomic nucleus, despite the electromagnetic force pushing protons apart, the weak nuclear force can change the identity, or flavor, of the quarks that make up these particles. In doing so, protons can be converted into neutrons, and vice versa, altering the stability of atomic nuclei.

While physicists have discovered new particles by colliding known ones at high speeds, placing known particles in extreme environments or configurations can allow quantum mechanics to produce bizarre behaviors, making them seem like new types of matter.

Simulations show that beneath the outer crust of these objects, the gravitational force is so extreme that atomic nuclei link together into chains of primarily neutrons and some protons called nuclear spaghetti. Deeper in the star, these links combine to form sheets—nuclear lasagna—a quintillion times stronger than steel, making it the strongest material in the universe.

While the electromagnetic, strong nuclear, and weak nuclear forces can be explained through interactions with particles, gravity is instead best modeled through spacetime curvature. Discovering a quantum particle of gravity would unite the two pillars of modern physics—quantum mechanics and general relativity—toward developing a theory of everything.

While gravity is the most familiar force, it is also the weakest and the only one without a particle to mediate the force. The weak nuclear force is responsible for radioactive decay and transmutation of elements, while the strong nuclear force holds quarks together.

In 440 BCE, Democritus proposed that everything was made up of tiny particles surrounded by empty space, which varied in size and shape based on the substance's properties. It was not until the 20th century that experimental evidence validated elements of Democritus' model.

Particles like electrons can exist in isolation, enabling them to move more freely. Within circuits, this allows electrons to carry energy across wire surfaces quickly. Contrastingly, light created in the sun's core is delayed by a million years on its way to Earth due to collisions with free electrons.

Originally thought to be indivisible spheres unique to each element, the discovery of the electron by J.J. Thomson revealed them to be made of smaller particles. Ernest Rutherford's gold foil experiment uncovered the existence of nuclei, which Niels Bohr suggested were surrounded by electrons in fixed orbits. By applying quantum mechanics, Erwin Schrödinger replaced orbits with probability clouds.

Quark-gluon plasma is a state of matter that formed shortly, very shortly, after the big bang. At one time filling the universe, scientists describe quark-gluon plasma as being similar to tap water, but only in the manner that such matter flows. Incredibly hot upon its emergence, it swiftly cooled and began forming the early building blocks of the universe.

Like a business whose purchased inventory matches sold inventory, physicists identified specific patterns across decades of particle accelerator data, which became new conservation laws for elementary particles. These laws help identify which particle decays are expected or forbidden.

At the beginning of the universe, high-energy photons prevented atomic nuclei from combining with electrons to form neutral atoms. Rather than waiting for the universe to expand and cool completely, a rare quantum phenomenon—a two-photon transition—allowed neutral hydrogen atoms to form sooner, expediting the formation of stars, planets, and life.

Observing high-angle deflections when alpha particles were fired at gold foil led to an atomic model with a dense, positively charged nucleus. Firing those particles at nitrogen resulted in the emission of hydrogen nuclei—protons—leading to the discovery of the subatomic particle.

While heavier elements like uranium and plutonium are unstable and decay quickly, simulations suggest a pocket of stability exists for elements with approximately 126 protons and 184 neutrons. Such elements may have practical applications, such as americium, a synthetic element used in smoke detectors.

In this simulation, users can add protons and neutrons to create an atomic nucleus, view its half-life and decay options, and identify patterns in how specific combinations of particles create extremely stable nuclei, from which the nuclear shell model of stability emerged.

The Higgs boson is a long sought after fundamental particle that—within the framework of high-energy physics—gives other particles their mass. Having captured public attention when it was discovered in 2012 at the Large Hadron Collider, and its...

Hydrogen, present since the early universe, serves as fuel for the proton-proton chain, producing helium, which is then incorporated into the CNO cycle to produce carbon, nitrogen, and oxygen. Additional fusions of helium with these elements and subsequent decays via the alpha ladder produce elements up to iron and bismuth.