Understanding time dilation

Time dilation explains that movement through space affects the passage of time

According to special relativity, everything in the universe moves through space-time at the speed of light. Just as turning from north to northwest on a road reduces one's northward motion, moving through space leaves less of this speed to move through time, causing an object to age more slowly.

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.

Space-time changes its shape and our perceptions of reality to maintain light's speed

To preserve the speed of light for all observers, the universe sacrifices the uniformity of space and time through the phenomena of time dilation and length contraction. This means that individuals may disagree on measurements of time and space based on their motion or location in a gravitational field.

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).

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.

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

The closer something is to the center of a massive object, the greater the strength of the massive object's gravitational field as a result of space-time being depressed more severely. Time passes more slowly the deeper an object is in this gravitational depression, meaning objects in the universe naturally seek to age more slowly.

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.

Time seems to stop for objects at the event horizon of black holes

At that location, the warping of space-time is so severe that the entirety of an object's space-time motion is solely through space, leaving it immobile in the time dimension. Faraway observers looking at the object would see it appear frozen before slowly dimming and reddening.

Time disappears when encompassing all quantum configurations across the universe

The Wheeler-DeWitt equation, a modified version of the Schödinger equation—the formula that describes the evolution of the quantum configuration of a system—describes the quantum state of space-time across the universe. The transformation causes the variable of time to disappear, suggesting it is not a fundamental, physical parameter of the cosmos.

Neil deGrasse Tyson explains wormholes and black holes

Much of the film Interstellar is centered on the existence of a wormhole and black hole, which happen to be two of the most perplexing things in the universe. Astrophysicist and StarTalk Radio host Neil deGrasse Tyson explains how wormholes and black holes work in real life in this two-minute video.

Delays in the decay of unstable particles provide evidence for time dilation

Physicists used the muon half-life measured in labs to predict how many should reach detectors on Earth's surface after their production in collisions between atmospheric molecules and cosmic rays. Higher detection rates were consistent with a longer half-life due to slower movement through time.

Understanding how and when time began requires a theory of quantum gravity

Rewinding the universe to the big bang compresses all matter, energy, space, and time into a single point, necessitating a model that combines general relativity with quantum mechanics. Although physicists understand time to have begun when the universe did, a clear understanding of the mechanisms involved remains unclear.

Massive objects can significantly bend light to produce gravitational lensing

The theory of general relativity posits that mass and energy bend space and slow down the passage of time. One consequence is that massive objects, such as black holes, curve spacetime to such an extent that light from background sources can loop around them, producing multiple images or ring-like patterns.

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

Because Earth exerts a stronger gravitational pull than the moon, it lags behind between 56 and 59 microseconds each day, or about one second every 46.5 years. This impacts essential synchronous operations of future electronic equipment on the lunar surface, which could be alleviated by a standardized conversion system between Earth and moon time zones.

A scale of the universe, from atoms to cosmos

Can you really appreciate just how small protons are, or how massive the universe is? To attempt to grasp it, watch this short video which zooms out from a young woman in California to the very limits of the cosmos using established scales. Then, dive deep into the atoms of her white blood cells for a fully-rounded effect.

Gravity Probe B verified that rotating objects drag spacetime

The experiment involved attaching four freely floating gyroscopes to a telescope aimed at a distant star for a year. The observed angular shift of the gyroscopes as a result of Earth's rotation pulling on spacetime was approximately 0.0000012 degrees from the amount predicted by general relativity.

The hypothetical particle that travels faster than light

Astrophysicists inspired by science fiction developed the theory of the tachyon—a Greek word for "fast"—which is a field or particle hypothetically able to travel faster than light. Although no experiments have confirmed any part of it, it's a fun theory to consider.

To develop general relativity, Einstein relied on his college friend, Marcel Grossman

Recognizing the mathematical complexities of generalizing special relativity with a new picture of gravity and acceleration, Albert Einstein had Grossman introduce him to tensor calculus. Years before developing the precursor to GR together, Einstein would use Grossman's lecture notes to prepare for his exams.

A scientific analysis of famous time travel stories

This 8-minute video explores how time travel influences the narrative arc of several movies, books and video games, from Harry Potter to A Christmas Carol. (Warning: it contains spoilers!) J.K. Rowling and Charles Dickens set myriad parameters as they’re worldbuilding to avoid paradoxes and create quasi-logical timelines. By drawing diagrams as he’s speaking, the video breaks down how time works in some of popular culture’s most beloved fictional universes.

Play a puzzle game where the speed of light is reduced to everyday speeds

In "Velocity Raptor," space and time warp as you make your way across a room of obstacles at "normal" speeds. Take advantage of these relativistic effects to solve puzzles involving clocks running at different rates and colors shifting as a result of your movement.

The impact of gravitational force on our bodies surprised early coaster riders and engineers

There is only a certain amount of gravitational force that the body can handle before dealing with consequences like short-term vision loss or unconsciousness. Increased scientific understanding has largely reduced these impacts, with engineers combining periods of intense pressure with periods of relief.

Four video explainers on quantum fundamentals

Ready to level up your working knowledge of quantum mechanics? Check out these four TED-Ed Lessons written by Chad Orzel, associate professor in the Department of Physics and Astronomy at Union College

Under the Big Rip scenario, dark energy becomes strong enough to tear atoms apart

If the density of dark energy, which produces a repulsive effect through the expansion of space, increases with time, then all structures of matter, including galaxies, stars, planets, and atoms, will be pulled apart once the strength of dark energy surpasses the magnitude of the forces holding those structures together, including the gravitational and electromagnetic forces.

The grandfather paradox of time travel

If you went back in time and killed your grandfather when he was a child, what would happen to you? One of your parents would never be born, so you wouldn’t be born either. But, if you’re never born, how could you kill your grandfather in the first place? This so-called grandfather paradox is something physicists, philosophers and sci-fi writers constantly ponder. Read the piece to learn how they’ve been trying to reconcile it.

Breaking down how and why 5G will change the world

The jump from 3G to 4G networks was pretty huge, and 4G to 5G is many times greater and is almost difficult to comprehend. This nine-minute video dives into how 5G will transform our world.

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

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Double world record holder Hunter Ewen helped conquer his fear of balloons, called globophobia, by training to win Guinness World Record titles for balloon inflation.

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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.

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