The double-slit experiment is observational evidence for the wave-particle duality

Wave-particle duality—a simple overview

Our notion of reality is built on everyday experiences. But wave-particle duality is so strange that we are forced to re-examine our common conceptions. Wave-particle duality refers to the fundamental…

Quantum mechanics explains how particles behave like both matter and waves

In the quantum world, particles such as electrons are “quantized,” meaning they can only hold specific values of energy or momentum. These particles also behave like waves, with their wave function predicting where they might be found at any moment as probability clouds called orbitals.

Light has been modeled as a wave and a stream of particles throughout history

Isaac Newton first identified white light as composed of a spectrum of colors, which he believed consisted of particles of different hues. Various light phenomena, including refraction, led Christiaan Huygens to develop an alternative wave model. Quantum mechanics validated both models through the concept of wave-particle duality.

The wave nature of matter can produce phenomena like negative time and retrocausality

Within quantum mechanics, matter simultaneously exists as both fixed particles and extended waves, allowing it to emerge across barriers—just as sound travels through walls—before it fully enters the obstacle. The resulting measurements can show that particles spent negative time within a barrier, with the future occurring before the past.

Quantum superposition makes Schrödinger’s cat both dead and alive until observed

Erwin Schrödinger's famous cat thought experiment illustrates how quantum objects can exist simultaneously in multiple states. This superposition allows electrons to behave as particles and waves, enabling chemical bonds and the function of modern electronics.

Watch the motion of an individual photon using a high-speed camera

Although light travels over 3 million football fields per second, cameras that capture trillions of frames per second can observe individual particles of light as they interact with atoms in materials they travel through. Such observations can be used to determine the speed of light in different materials.

Light appears to slow down as it travels through different materials

As electromagnetic waves interact with particles in a transparent medium, particles vibrate and generate their own electromagnetic waves. The interference of the original and generated waves, which are slightly delayed, results in ensemble light with an effective slower speed but unchanged color.

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

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.

Spikes of light around stars are artifacts of light bending around the mirror supports

Through diffraction, electromagnetic waves can bend around obstacles, as observed in the silver linings at the edges of clouds, where light should be blocked. Within reflecting telescopes, starlight diffracts around struts—beams holding a secondary mirror in place—and spreads perpendicular to them, creating pairs of spikes.

Particle detection has evolved from cloud and bubble chambers to digital 3D displays

As invisible particles passed through cloud and bubble chambers, they disrupted supersaturated vapor and superheated liquid, respectively, creating trails that served as proxies for cosmic rays. The transition from photographed events to digital sensors enhanced data collection and accuracy.

Spectroscopy lets scientists analyze an object's light to determine its properties

By separating the light spectrum into its component wavelengths and comparing them to what is expected based on Earth-based experiments, we can determine an object's temperature, elemental and molecular composition, and motion through space.

One of Einstein's papers challenged quantum theory but helped confirm entanglement

In 1935, Einstein suggested that quantum mechanics was incomplete due to its strange implications about entangled particles. Their challenge led to decades of experiments that eventually proved distant particles could affect each other instantly.

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.

Stimulating electrons to emit identical photons produces lasers

This effect was predicted by Albert Einstein in 1917, and requires all excited electrons in a material to exist in the same excited metastable state within their atoms. Pumping all atoms through the same mechanism, such as electricity or flash lamps, can create this environment.

Einstein’s theory of special relativity

Special relativity, formulated by Einstein, describes how space and time are linked for objects moving at constant speeds. It states that the speed of light is constant for all observers, leading to time dilation (moving clocks run slower), length contraction (moving objects shrink), and mass-energy equivalence (E = mc²). This video breaks down how motion and time are fundamentally related.

Explore an optical table to create quantum physics experiments

This interactive teaches users to create quantum experiments through lessons resembling video game levels. Users can also use the virtual lab to visualize landmark quantum experiments like entanglement, teleportation, cryptography, and quantum computing, or create their own experiments with drag-and-drop elements.

X-ray diffraction reveals atomic structures by analyzing how crystals scatter X-rays

X-ray diffraction involves rotating a crystal in an X-ray beam while a detector captures the resulting diffraction patterns, which depend on the crystal’s internal structure. The mathematical principles behind the technique won the 1915 Nobel Prize and improved crystallography.

Humans experience the world subjectively. What does that mean for scientific research?

When you close your eyes, do you see static or colorful patterns or an "intrinsic grey" known as Eigengrau in German? This variation of our internal experiences is just the tip of the iceberg, one that scientists are increasingly studying and...

Holograms are produced by shining light through recordings of interference patterns

When one half of a split laser beam that was reflected off the surface of an object recombines with its other, unreflected half, the two produce an interference pattern that becomes etched onto holographic film. When light shines through the back of the film, it reacts with the pattern to create the reflected light, projecting the original object.

Observations of Jupiter's moons first demonstrated that light was not instantaneous

In 1676, Danish astronomer Ole Rømer noticed that eclipses of the moons occurred several minutes later when Earth and Jupiter were farther apart, reasoning that light needed more time to travel the greater distance. Lacking knowledge of Earth's orbital diameter, he was unable to calculate the speed of light.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

The selfie camera exists thanks to Einstein's discovery of the photoelectric effect

Smartphone cameras utilize sensors such as CMOS or CCD to capture light by converting it into electrical signals through the photoelectric effect. Einstein explained this effect by demonstrating that light behaves as both particles and waves simultaneously, a discovery that earned him the Nobel Prize in physics.

Synchrotron radiation has revealed the fur color of creatures millions of years old

When electrons are accelerated in the loop, they produce intense X-rays that can reveal properties of a sample struck by them, just as X-rays can be used to show bone structure in humans. Studying the reflected light from fossils can uncover the presence of known pigmentation compounds.

In 1974, a pair of neutron stars provided the first evidence of gravitational waves

Observations of a pulsar—a rapidly rotating neutron star that emits light—revealed it to be part of a system of two stars that orbited one another in a shrinking orbit, indicating gradual energy loss. Calculations showed that the changing orbit was consistent with gravitational waves predicted to carry energy away from such a system.

As of 2025, LUX-ZEPLIN is the world's most sensitive dark matter experiment

The experiment is designed to indirectly detect WIMPs—weakly interacting massive particles and a candidate for what dark matter is made of—by looking for light produced when they collide with xenon atoms. Such collisions would also release electrons, which are then manipulated to produce a secondary light signal that helps rule out background effects.

Understanding ball lightning remains an area of active research

Observations of glowing orbs of light that appear during or after thunderstorms have been documented since at least the 12th century, but their rarity and short lifetimes have made their study challenging. Some theories suggest they form when lightning vaporizes pockets of gases in the air or certain materials on the ground.

Stars appear to twinkle because turbulence in the motion of molecules in Earth's atmosphere causes light to bend and wiggle rapidly on its way to the surface—a phenomenon called scintillation.

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.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Massive blooms of microscopic plankton called dinoflagellates produce the neon blue light seen in glowing tides.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

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

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

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

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.'

A pickleball's loud 'pop' sound can reach 120 decibels, which is equivalent to a hammer hitting a nail

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.

Ebola is a filovirus, meaning it resembles a thread under a microscope, though it sometimes twists and can resemble a bowl of spaghetti.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

The first horror movie is believed to be George Méliès' 1986 short 'The Haunted Castle,' which pioneered the use of special effects

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

Sony set the standard for cylinder-shaped batteries when it repurposed manufacturing equipment used to make rolls of magnetic recording tape.

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.

Browse a detailed visual analysis of over 200,000 similes—comparisons that often use 'like' or 'as'—from popular fiction to see how frequently writers the same idiomatic expressions.

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

Many legends about George Washington, including his supposed wooden teeth and the story of cutting down the cherry tree, lack evidence.

The Beatles' US label rejected the band's first two singles, 'Please Please Me' and 'From Me to You,' with one executive calling the band 'dead in the water.'