By changing one's frame of reference in special relativity, electric forces can be reinterpreted as magnetic forces, highlighting how the two together constitute electromagnetism.

Discoveries in electromagnetism, which suggested that light traveled at a single speed, became the catalyst for overturning Isaac Newton's view that all speeds are relative.

The speed of electricity may refer to the movement of electrons, which is on the order of a fraction of a millimeter per second, or energy, which is near the speed of light.

Individuals moving at different speeds may disagree on the order of observed events because each experiences the passage of time differently, according to special relativity.

In the 1910s, physicists proved that the existing laws of physics made it impossible for solid magnets to exist—a finding overturned by quantum mechanics.

Within Einstein's picture of the universe, gravity is technically not a force because forces cause accelerations that deviate objects from their natural path, and moving solely due to gravity is natural.

Watch a timeline of the history of electricity, from observations of static electricity in antiquity to the War of the Currents—a rivalry to establish the ideal system for electric grids.

Wireless charging uses a magnetic field to move charged particles in a battery

The centrifugal force is associated with the feeling of being pushed outward when moving in a circle, but it is a fictitious force arising from objects' tendency to move in straight lines.

Certain objects are magnetic because their electrons' magnetic moment—an intrinsic quantum property—align within the object in specific patterns.

Special relativity shows how motion at high speeds reshapes time, space, and energy

Electricity can flow indefinitely along a ring of superconducting material, which provides zero resistance to the movement of charges due to quantum effects.

While special relativity describes motion along flat spacetime—the underlying fabric of the universe—general relativity extends this theory to explain motion through curved spacetime.

You have never made physical contact with anything in your life because electrons in the outer layer of atoms on the surface of objects repel one another.

Electromagnetic induction creates electricity from a changing magnetic field

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

According to the equivalence principle, objects in a closed space cannot tell the difference between whether they are accelerating or experiencing a uniform gravitational field.

Albert Einstein's theory of gravity arose from what he described as 'the happiest thought of his life': realizing that a person who fell off the roof of their house would not feel their own weight as they fell.

According to the special theory of relativity, the faster objects move through space, the less they move through time, and therefore age more slowly.

The magnetic constant sets the strength of magnetic fields

For the speed of light to be constant for all observers, space and time cannot be absolute, universal dimensions that are identical for everyone.

Explore how excitatory cells, such as neurons and muscle cells, transmit information in the body via electrochemical signals, which can travel up to 120 meters (390 feet) per second.

Molten metal moving around Earth's inner core creates the planet's magnetic field, whose north and south poles do not align with the planet's geographic poles.

Almost three centuries before Albert Einstein presented the special theory of relativity, Galileo Galilei devised a principle of relativity involving uniform motion.

The one-electron theory describes the universe as having only one electron

Because they move at the cosmic speed limit through space, photons—particles of light—do not 'perceive' distance or the passage of time.

Measurements of an electron’s magnetic moment help test the Standard Model

While charges consistently move in the same direction in a direct current, the flow of charges changes multiple times per second in an alternating current.

Electricity is produced when the ends of a battery are connected by a conducting wire, triggering chemical reactions that release the energy stored in chemical bonds.

Although moving through space faster than the speed of light is forbidden by special relativity, dark energy causes about 97% of galaxies to appear to do so.

Transformers change the current and voltage across a set of wires by wrapping them around a magnetic core and using the magnetic field of one wire to induce a current in the other.

Antimatter particles possess the same mass and spin as their normal particle counterparts, but possess an opposite charge and transform into pure energy upon colliding with normal matter.

Visualizing Einstein's special relativity

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

Photons are both particles of light and messengers of the electromagnetic force

The underlying fabric of the universe—spacetime—changes shape in the presence of mass and energy, which affects measurements of space and time.

Learn why magnets, like statically charged balloons, can deflect water

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

Simulate the buildup and discharge of static electricity through friction by dragging the arm and leg of 'John Travoltage' along surfaces.

Visualize how alternating currents—electricity that periodically changes direction—are generated by rotating magnetic fields, as occurs in turbine-generator systems.

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

Classical mechanics describes the motion of and forces on everyday objects

Distinguishing polar and nonpolar molecules and why charges get distributed unevenly in molecules

Virtual particles are bookkeeping tools used to describe force interactions

By combining special relativity with quantum mechanics, antimatter was predicted four years before it was observed, though the math suggested it possessed negative energy.

Fluxgate magnetometers detect magnetic fields using electromagnets

Research shows that cosmic rays may trigger the cascade of displaced electrons needed to produce lightning, which is also enabled by pointed ice crystals that create strong electric fields.

Earth's magnetic field, which deflects charged particles, helps protect us from cosmic rays, but the sensitivity of these particles to magnetic fields also makes it difficult for astronomers to determine their sources.

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

Quantum mechanics and general relativity—two of the most successful explanations of the physics seen across the universe—are logically incompatible with one another because they use contradictory models for space and time.

Tachyons are theoretical particles that travel through space faster than light