Gravity Probe B verified that rotating objects drag spacetime

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

Besides accurately explaining the slight wobble observed in Mercury's orbit, general relativity predicted that light would bend around massive objects by an amount matching what was observed when background starlight bent around the sun during an eclipse. The theory also predicted the existence of gravitational waves and black holes decades before they were found.

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

Without interventions to boost the observatory to a higher orbit, Hubble is expected to fall to Earth's surface in the mid-2030s. In the meantime, the telescope is expected to continue to be productive by shifting its mode of operation to rely on a single gyroscope, down from three.

Experimenting with space-time

Einstein's theory of general relativity—that mass literally bends space and time—can be difficult for the human brain to imagine. This interactive resource lets you create celestial objects, imagine their effect on space-time, and see how they interact with each other (best viewed on desktop).

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.

Gravity travels at the speed of light

Isaac Newton believed that gravity acted instantaneously between objects with mass, whereas Albert Einstein suggested that spacetime curvature reacted at the universal speed limit. Observations of colliding neutron stars by the Laser Interferometer Gravitational-Wave Observatory in 2017 confirmed Einstein's prediction.

Simulate the precession of Mercury's perihelion

The location of Mercury's closest point to the sun shifted in the sky at a rate of approximately 0.16 degrees per century, or 0.012 degrees more than what was predicted by Isaac Newton due to the gravity of the other planets. General relativity correctly predicted this shift.

GPS satellites are programmed to account for their faster passage of time in space

The Global Positioning System relies on signals from satellites to calculate locations on Earth by measuring time and distance. However, their orbits, being farther from Earth's center, cause them to experience less gravitational time dilation. These systems would be off by 11 kilometers per day without relativistic corrections.

The extreme precision of atomic clocks highlights gravitational time dilation

Scientists at the National Institute of Standards and Technology have constructed clocks made out of stacked strontium atoms, which show differences in the passage of time across just a millimeter of height consistent with predictions from general relativity, where atoms closer to Earth's center tick off time more slowly.

Earth's smooth, continuous motion as it orbits the sun prevents detectable motion

Although humans are sensitive to acceleration, Earth's nearly circular orbit around the sun and its slow spin relative to its size produce negligibly small, minimally changing accelerations. However, the changing seasons and the day-night cycle are evidence of Earth's movement through space, as verified by satellites and telescopes.

Gravity assists are crucial for space travel beyond Mars

By traveling near a moving celestial object, a passing object can gain or lose speed and change direction due to the acceleration provided by their mutual gravity. Some missions are planned around spacecraft performing multiple assists, or slingshots, to reduce fuel requirements for long-distance travel.

Explaining why the Earth wobbles

Astronomers going back to Hipparchus in the 2nd century BCE have noticed our planet has a distinct wobble. More recently, scientists have observed that the Earth is 26 miles wider at the equator than from pole to pole. The wobble results from our...

Explaining pulsars, the cosmic clocks and lighthouses of the universe

As of 2023, over 3,000 of these rapidly rotating neutron stars have been discovered, which contain magnetic fields along which energized particles accelerate and emit light, including X-rays, gamma rays, visible light, and, most commonly, radio waves. The fastest of these, PSR J1748–2446ad, rotates 716 times per second, meaning its surface equator moves at about 24% the speed of light.

The European Space Agency is building a space-based gravitational wave observatory

The Laser Interferometer Space Antenna will consist of three spacecraft forming an equilateral triangle that will trail Earth as it orbits the sun. Lasers will travel 2.5 million kilometers along the sides of the triangle between these spacecraft to detect massive objects undergoing mergers or inspiraling, as well as speculative phenomena (e.g., cosmic strings).

Understanding time dilation

The faster you go, the slower time ticks for you. And the stronger the gravitational field acting on you, the slower time ticks for you. These phenomena – collectively called time dilation – were first explained by Albert Einstein’s theories of general and special relativity. In this 11-minute video, beloved astrophysicist Neil deGrasse Tyson explains them to comedian Chuck Nice.

The first interferometric gravitational wave detector was invented in 1972

Robert Weiss completed the designs after his students asked about an earlier apparatus that used stretched aluminum cylinders to detect passing gravitational waves. Unfamiliar with general relativity and hoping to keep the course focused on experimental tests rather than mathematics, Reiss later asked his students to consider his device for homework. (Some readers may experience a paywall.)

Modified Newtonian dynamics revises gravity to eliminate the need for dark matter

Rather than imagining that an undiscovered particle is responsible for discrepancies in the orbits of stars and galaxies, MOND suggests that the mathematics underlying Newton's laws of gravity and force change beyond a certain scale. However, the suggested revisions struggle to explain relativistic effects involving gravity, including gravitational lensing and gravitational waves.

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.

Space probes propelled by lasers may one day visit distant planetary systems

Launched in 2016, Breakthrough Starshot is a project to send gram-sized spacecraft to the nearest stars and their planets at 10% to 20% the speed of light after being accelerated by ground-based laser systems. The project requires orders of magnitude advancements to current technology.

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

Gaia mapped two billion stars in the Milky Way

Using geometric parallax, the European Space Agency mission made position measurements accurate to 2.78 × 10⁻¹⁰ degrees, revealing large-scale galactic structure and dynamics. Remnants of ancient galactic mergers were also identified within the Milky Way.

Through 2025, two-thirds of known exoplanets have been detected via transits

This technique involves observing periodic, consistent dips in a star's brightness caused by an exoplanet passing in front of it. Observing wobbles in a star as it is pulled by an orbiting exoplanet's gravity has become the second most common detection method, followed by microlensing and direct exoplanet observation.

Objects moving relative to one another will not agree on the simultaneity of events

Space and time shift when switching from a nonmoving to a moving perspective, causing events that seem to occur simultaneously for one person not to appear that way for someone else. This also means one person's present could be another's future, ensuring all of time already exists.

Differential rotation and density waves create the arms of spiral galaxies

Stars and gas near the galaxy's center complete an orbit in less time than objects farther out. Pressure waves cause material to bunch, lagging behind stars and gas that orbit closer to the center and forming the arms.

There are statistically significant discrepancies in measured universal expansion

Using data from the cosmic microwave background, which allows astronomers to model the universe's conditions since its earliest moments, yields a rate of expansion—the Hubble constant—lower than values obtained from multiple techniques measured locally at more recent timescales. Reconciling the discrepancy, known as the Hubble tension, will require a third independent measurement method between the two scales

Galileo's Jupiter discovery shattered Earth-centered universe beliefs

Using a telescope inspired by Dutch designs, Galileo spotted four moons orbiting Jupiter in 1610, providing undeniable evidence against geocentrism and fueled support for the heliocentric model. Galileo’s original telescope design stretched 20 meters long—a feat of optical engineering for its time.

Evidence for a ninth planet in our solar system

Is there a massive ninth planet on the edge of our solar system? Many of our solar system's most distant objects tend to swing out in one direction, hinting at evidence for a previously unknown ninth planet potentially larger than Earth. This theoretical planet's orbital period is estimated to be roughly 20,000 years, revolving around the sun at a distance of 60 billion miles. Experts break down the evidence in this quick video.

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

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.

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

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.

The first image of a black hole was captured by creating an Earth-sized virtual observatory from a network of eight radio telescopes.

Explore our favorite visualization of the immense scale of space, from an astronaut to the size of the observable universe

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

Astronauts have repaired genetic damage in space using CRISPR—a molecular tool that can make precise changes to DNA and is used in single-celled organisms to attack invasive viruses.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

After 25 people used virtual reality headsets to practice flying with virtual wings—flapping their arms—their visual cortex responded to the wings almost as if they were real arms, treating them as body parts.

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

Against his wishes, Albert Einstein's brain was removed before his cremation, and the pathologist responsible stored it for decades in mason jars within a beer cooler.

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.

SpaceX's S-1 or 'prospectus' revealed many previously unknown details about the company, including its unprofitability despite doing $18.7B in revenue in 2025, exactly how many voting shares Elon Musk will have in the company (roughly 85%), and more.

One disco producer saw 'Star Wars' four times on its opening weekend and was so inspired that he recorded the album 'Star Wars and Other Intergalactic Funk,' which produced a chart-topping single.

In 2009, the nation was gripped by the story of a missing young boy who was believed to be floating over Colorado in a homemade balloon, until it was revealed that he was at home the whole time.

In 1984, Operation Smash Hit intentionally crashed a 239-ton train into a nuclear waste canister at 100 miles per hour to prove the canister's safety, which remained completely intact and lost just 0.29 of its 100 pounds of pressure.

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.

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time

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.

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.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.