Gravity, electromagnetism, and two nuclear forces make up nature’s fundamental forces

An explanation of the weak nuclear force, which can induce some forms of radioactive decay

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.

The graviton may be the last missing piece of the Standard Model

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.

Why most atoms do not spontaneously break apart, despite protons repelling one another

At small scales, the strong nuclear force overwhelms electromagnetic repulsion between positively charged particles, keeping the nucleus intact. However, because the force's range is limited, it cannot provide the attraction needed to hold onto protons that are spread out across very large atomic nuclei.

What is gravity made of?

Our world at very small scales is governed by quantum mechanics, in which forces and energy come in discrete packets. At large scales, our world is governed by gravity, which moves the planets and stars and can create waves in spacetime. To merge...

The Standard Model reveals an underlying organization to the universe

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.

The Higgs boson provides a mechanism that explains why some particles have mass

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.

Virtual particles are bookkeeping tools used to describe force interactions

Physicists mathematically describe the electromagnetic, weak nuclear, and strong nuclear forces as the result of these particles being exchanged between particles of matter. Despite not being real, observable particles, this method has provided experimental predictions with an accuracy of over 12 decimal places.

LIGO can detect changes in spacetime one ten-thousandth the width of a proton

Gravity is the weakest of the fundamental forces in nature, meaning the length of objects only changes by minuscule amounts as gravitational waves ripple through space from distant, albeit massive, cosmic events. LIGO's sensitivity can measure an object shifting its position by one seven-hundred-trillionth of the width of a human hair.

Learn about the history of quarks, found deep in the heart of every atom

Independently theorized by American physicists Murray Gell-Mann and George Zweig in 1964, experiments later showed that these particles come in six varieties, named up, down, top, bottom, charm, and strange. Combinations of these quarks, which are held together by mediators of the strong nuclear force—gluons—make up dozens of composite particles, including protons and neutrons in atoms.

According to general relativity, gravity is technically not a force

Forces are traditionally viewed as interactions that cause accelerations, such as the force between two magnets pulling them together or pushing them apart. General relativity reframes acceleration by describing motion along the curves of spacetime as natural, and only deviations from those paths require forces.

Models of the strong nuclear force resemble the RGB color system

Quarks are described as having “color charge” and must combine to produce color-neutral particles (e.g., red + anti-red = white). An isolated quark, which would create a colored particle, is impossible because the energy to overcome strong force particles—gluons—is enough to generate more quarks to maintain color neutrality.

The features of neutrinos, the second most abundant particles in the universe

Fundamental particles produced during nuclear interactions, such as those within stars and particle accelerators, neutrinos have almost no mass, rarely interact with other particles, and come in three varieties, or flavors. Each type can change into the others as it travels through space, a process called neutrino oscillation.

Dark matter's limited force interactions make its detection difficult

Despite making up the vast majority of matter in the universe, dark matter can only be directed indirectly via its influence on other objects through gravity, the weakest of the fundamental forces. This means direct detection of dark matter may only be possible with future, more sensitive instruments.

Leptons do not experience the strong nuclear force that binds quarks together

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.

A look inside neutron stars, which are thought to contain nuclear pasta

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.

Why quantum mechanics keeps gravity from collapsing neutron stars into black holes

According to the Pauli exclusion principle, certain particles, such as neutrons, are forbidden from occupying identical states within a system. Like tennis balls tightly packed together, neutrons exert a resistive pressure against this compression—neutron degeneracy pressure—which can help prevent gravitational collapse. (Some readers may experience a paywall.)

Quantum mechanical principles are responsible for chemical properties

Besides quantization, the wave-particle duality, and probabilistic features, quantum theory's mathematics introduces the exclusion principle, quantum tunneling, quantum entanglement, and other phenomena foreign to our everyday experiences. Some suggest that all possibilities for a quantum system may also occur across the multiverse.

View summaries of the most common types of radioactive decay and their associated particles

The alpha particle has the strongest ability to ionize other atoms it strikes, but it also does not travel very far before colliding with something and being absorbed. Gamma particles—high-energy photons—do not interact with matter as easily and therefore possess the greatest penetrating power, though this also makes their ionizing potential the smallest.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

Newton's laws describe how objects resist acceleration and respond to forces

Newton’s first law defines inertia as the tendency of an object to maintain its velocity. His second law connects external force, inertia, and acceleration, while his third law states that forces come in pairs—every action has an equal and opposite reaction.

Understanding how atomic structure contributes to each element's properties

The outermost layer of electrons in an atom dictates how it will bond to other atoms. These bonds determine whether elements exist as solids, liquids, or gases in the environment and other characteristics. For example, electrons are freely shared between atoms in metallic bonds, allowing them to immediately re-emit light that strikes them, thus making most metals shiny.

The magnetic constant sets the strength of magnetic fields

The permeability of free space, or μ₀, contributes to the speed of light in the universe—a fundamental constant. It also helps quantify how the movement of electric charges generates a magnetic field and vice versa.

Electromagnetic repulsion prevents objects from making contact with one another

The feeling of touching something is a sensation caused by the electromagnetic force between the electrons on the surface of objects. Since this force grows to infinity with proximity, no two surfaces can ever achieve matter-to-matter contact.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

Earth is the only terrestrial planet with a magnetic field

Its magnetosphere emerges from a complex interior process of electrical conduction, heat, and motion known as the geodynamo. The magnetic field shields the Earth from unsafe cosmic radiation, providing one of the many conditions required for life.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

The discovery of nuclear fission was facilitated by the discovery of the neutron

The discovery of the neutron provided scientists with a particle that could penetrate the nucleus and advance atomic physics. Otto Hahn was the sole Nobel recipient for the discovery of fission, despite collaborating with Lise Meitner and Fritz Strassmann.

Earth's total mass is equivalent to 13 quadrillion Egyptian pyramids of Khafre

Newton's law of universal gravitation was used to calculate the value after Henry Cavendish torsion balance experiments determined the missing value of the universal gravitational constant from Newton's equation.

Neutron stars, the remains of some massive stars after they explode in a supernova, are the densest directly observable objects in the universe.

Most of the observable universe's volume consists of voids and supervoids—enormous regions of space with little to no galaxies, stars, or light.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

For centuries, Niagara Falls has been a magnet for daredevils seeking to conquer one of nature's most powerful wonders, with its 200-foot drop and water rushing at 32 feet per second with 280 tons of force.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

See how fireworks are made and learn how metals like magnesium and copper are responsible for different colors.

The price of gas is a composite made up of several different factors, with the federal gas tax making up less than 20% of what drivers pay at the pump.

The US dollar is the most widely circulated currency in the world, and is involved in nearly 90% of global transactions

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

The Nasdaq's 'Magnificent 7' companies are responsible for roughly 40% of the Nasdaq 100 index's gains, while the remaining 93 companies account for the other 60%.

See the 25 of the best photos of auroras from around the world.

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.

After NASA's Voyager 1 captured Earth as a single pixel as it left the solar system in 1990, astronomer Carl Sagan used the image to reflect on humanity's fragility and the responsibility to protect 'the only world we've ever known.'

Lesser-known phobias include turophobia, or the fear of cheese, and nomophobia, the fear of being without your cell phone.

The rivalry between Alexander Hamilton and Thomas Jefferson centered on federalism—the question of how much power the federal government should hold relative to the states.

Three Ebola species are responsible for most large outbreaks of the disease, yet the only approved Ebola vaccine is known to work against just one of them.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

Exploring the Larry Bird punch that almost changed March Madness

SpongeBob exemplifies Aristotle's philosophy for living well because he understands that happiness doesn't come from external factors like money, recognition, or power.

The Brothers Grimm were lawyers before they were storytellers, and became interested in fairy tales as they began investigating how rules and customs had been passed down through cultures.