GPS satellites would fail within minutes if they didn't recalibrate according to Einstein's theories of relativity.

Scientists showed that the relativistic effect of time dilation was real after comparing atomic clocks flown around the world with stationary ones on Earth's surface.

Earth's core is about 2.5 years younger than its surface according to relativity

The extreme precision of atomic clocks highlights gravitational time dilation

Gravity Probe B verified that rotating objects drag spacetime

Scientists validated Albert Einstein's theory of gravity by measuring the apparent positions of stars via their starlight as it traveled near the sun on its way to Earth during a total solar eclipse.

Uncertainties in measurements make finding gravity's Newtonian limit unclear

Satellites in low Earth orbit can experience changes in their orbits due to shifts in solar activity, which alter the amount of energy Earth's atmosphere receives and its resulting density.

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

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.

How neutron stars serve as laboratories for testing Einstein's theory of gravity

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

Experimenting with space-time

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

A breakdown of the experimental test results supporting the general theory of relativity

By discarding absolute space and time, special relativity introduces paradoxes—scenarios in which different, equally valid observers obtain conflicting measurements—such as the twin and ladder paradoxes.

When GPS and sonar are unavailable, submarine navigation relies on a fiber-optic gyroscope to determine the vessel's orientation and an accelerometer to calculate distance traveled.

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

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.

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

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

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.

Although associated with his theories of relativity, Albert Einstein initially viewed the concept of spacetime, which originated with his teacher, Hermann Minkowski, negatively.

Earth's rotation rate constantly changes, which drove the need for leap seconds to synchronize a solar day with timekeeping tools.

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

Einstein created a mathematical term for anti-gravity to keep the universe static

Mathematician David Hilbert developed general relativity equations before Einstein

Potential LIGO sites were selected in pairs, approximately 3,000 kilometers apart

By measuring radio signals transmitted to and received from distant spacecraft, NASA's Deep Space Network can determine a spacecraft's position and speed and send commands to alter its trajectory.

Increasing amounts of space debris in low Earth orbit risk triggering Kessler syndrome, in which debris density becomes so high that orbital regions become unusable.

No map of the Earth is perfect because each introduces inaccuracies in the shape, size, or orientation of landmasses and oceans by trying to flatten the planet's curved surface.

Simulate the precession of Mercury's perihelion—the gradual shift in the closest point of Mercury's path around the sun as its elliptical orbit rotates.

Why time ticks faster on the moon, which may need its own time zone

The geoid depicts what Earth would look like if not for tides and currents, given the planet's rotation and uneven gravitational field.

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.

Where you are located in a gravitational field affects how quickly you age

Gravitational waves—ripples in spacetime that result from the motion of objects—were detected a century after Albert Einstein predicted their existence upon developing his theory of gravity.

Five surprising things your GPS can do

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

Atmospheric drag is causing the Hubble Space Telescope to drift toward Earth slowly

The construction of LIGO needed to compensate for Earth's curvature

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

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

Because some models of the universe do not incorporate time, it may be an emergent property born from our limited perception of the universe, rather than a fundamental property of reality.

Scientists determine earthquake locations by comparing how long it takes different seismic waves to be detected at three stations around the world, from which an origin, or hypocenter, can be triangulated.

Explaining pulsars, the cosmic clocks and lighthouses of the universe

Watch a visualization of what it would look like to move along Earth's surface as fast as the International Space Station, or about 23 times the speed of sound.

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.

Exploding white dwarfs, spinning galaxies, and the expansion of the universe are used by astronomers to measure distances across the cosmos.

Why atoms are used to keep track of time and define the meaning of a second