Particles moving faster than the speed of light give nuclear reactors an eerie blue glow.

Light appears to slow down as it travels through different materials

Light appears to slow as it travels through transparent materials due to interactions with the charged particles in the atoms of the material.

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

Electrical energy transfers at near light speed, even though the electrons carrying the energy in circuits only move a fraction of a millimeter per second.

Objects that move faster than the speed of sound—Mach 1—create shockwaves called sonic booms by building up and forcing sound waves to combine as they lag behind the object.

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

Cosmic rays are thought to be accelerated to near the speed of light by repeatedly bouncing across shockwaves produced by high-energy cosmic events, such as supernovae.

Watch some effects of special relativity become increasingly more apparent in 'A Slower Speed of Light,' a video game prototype from the MIT Game Lab.

Although the color of light changes due to motion between a source and an observer—the Doppler effect—relativistic motion further alters it due to time dilation.

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

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

Gold has a yellowish appearance rather than the silvery color of most metals because of special relativity, which causes gold's electrons to absorb blue light.

A spaceship traveling near the speed of light would experience relativistic aberration—its field of view will seemingly narrow into the direction of travel.

In nuclear reactors, water acts as a coolant and moderator, slowing neutrons produced in nuclear reactions so they are more likely to interact with nuclear fuel and generate sustainable energy.

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

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 hypothetical particle that travels faster than light

View the electromagnetic spectrum and the properties of different types of light

View an animation of how certain chemicals fluoresce—that is, emit visible light after having absorbed higher-energy light, such as ultraviolet radiation.

Light takes approximately eight minutes to travel from the sun's surface to Earth, but it takes thousands of years to reach the star's surface from its core—a distance more than 200 times shorter.

The finite speed of light means we can only perceive the world's past

Observations of colliding neutron stars by the Laser Interferometer Gravitational-Wave Observatory in 2017 confirmed that gravity travels at the speed of light.

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.

Explaining pulsars, the cosmic clocks and lighthouses of the universe

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

Relative motion between a source and an observer shifts the color of observed light

While atomic clocks measure time using the movement of electrons between energy levels, nuclear clocks track energy shifts within atomic nuclei to achieve greater accuracy.

Although they rely on radioactive elements to operate, everyday technologies such as electronic exit signs, some wristwatches, and smoke detectors are not dangerous, unless they are damaged and their radioactive material is inhaled or swallowed.

Walk around Relativity Park—a virtual theme park where you can experience relativistic effects by slowing down the speed of light.

If a source of music traveled past someone at twice the speed of sound, assuming sufficiently sensitive hearing and powerful equipment, they would hear the music backward.

Particles produced in cosmic-ray showers that would normally decay long before reaching Earth's surface are observed by ground-based detectors, as predicted by special relativity.

Fireworks make a loud booming sound after explosion due to air expanding faster than the speed of sound.

The deaths of massive stars and the mergers of neutron stars and black holes can produce gamma-ray bursts—jets of particles moving in opposite directions at near-light speed that comprise the universe's most powerful explosions.

Tachyons are theoretical particles that travel through space faster than light

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

Lasers can be used to reduce the motion of atoms because particles of light—photons—can collide with particles of matter, as billiard balls do, to slow them down.

Everything with a temperature above absolute zero emits light at nearly all wavelengths

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

Through sonoluminescence, concentrated sound waves can produce short, high-intensity flashes of light by rapidly collapsing microscopic bubbles to temperatures up to twice that of the sun's surface.

Blacklights can illuminate certain biological materials, including blood, teeth, and fingernails, because they contain fluorophores—molecules that visibly glow immediately after exposure to higher-energy light.

Trillions of neutrinos travel through your body every second without leaving a trace.

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

By analyzing the color of starlight, astronomers can determine how fast stars within a galaxy are moving toward or away from Earth, revealing the expansion rate of the universe.

You can measure the speed of light with a microwave oven and chocolate, cheese, or other uniformly thick foods.

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.

Visualize how the order of events changes, according to special relativity, when the perspective is changed between observers who move relative to one another.

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

Visualizing the chemistry of nuclear weapons

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

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.