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The Real Effects of Lightyear’s Time Dilation

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Spoiler alert: This article discusses a major plot point in the 2022 Disney Pixar film Lightyear.

The new Disney Pixar movie Light year is packed with sentient robots, laser blades and lightning-fast travel and there’s plenty of cool science to go along with all that fun fiction.

At the beginning of the film, we join Buzz Lightyear and his team on a trip. They are marooned on a hostile planet 4.2 million light years from Earth and their only chance of escape is to develop a special fuel that will allow them to travel fast, very fast. Buzz, the brave Space Ranger, volunteers to test the fuel. After his first flight, he returns to find that if it had only been a few minutes for him, everyone on the planet would have aged several years. With each subsequent test flight, each reaching faster and faster speeds, Buzz returns to find that more and more time has passed.

Buzz eventually learns that he experienced something called time dilation. This actual phenomenon causes time to pass more slowly for someone who is moving, compared to someone who is standing still. And the greater the difference in speed, the greater the difference in time. If, like Buzz, the mover returns to their original location, it can feel like they have traveled to the future. Or, as Buzz explains, “The faster I fly, the further I travel into the future.”

Photo credit: Disney/Pixar

Albert Einstein, with his special and general relativity theories published in 1905 and 1916, showed that time dilation can be caused by two things: differences in speed and differences in distance from a strong gravitational field. If you were to approach a black hole, for example, with a very strong gravitational pull on the space around it, time would move more slowly as you approached it. Both types of time dilation have been shown in dizzying effects in movies and television for decades, where they provide a means of seemingly time travel.

Time dilation is the most noticeable and causes the biggest time jumps at high speeds or near a very strong gravitational field, but we all experience time dilation every day. In 2010, physicists at the National Institute of Standards and Technology used highly accurate clocks to show that clocks will run slower even at speeds as slow as 25 miles per hour and height differences as small as a foot. So when you’re standing on Earth, your upper body moves a bit faster than your lower body because of the Earth’s rotation, but your feet feel a stronger gravitational pull toward Earth than your head. The two effects of time dilation clash here, but gravitational time dilation is stronger, making your head look older than your feet. If you fly from Boston to Los Angeles, you will age faster than people on the ground. However, once you’re back home and flying from Los Angeles to Boston, you’ll age more slowly, due to the extra speed you’ll gain as you move with the Earth’s rotation.

These time differences are incredibly small, and you won’t notice the occasional change in the rate of aging, but what about astronauts circling the Earth in space? Those aboard the International Space Station (ISS) orbit the Earth at 17,500 miles per hour. That’s almost 5 miles every second! Astronauts returning to Earth after 6 months on the ISS will have aged more slowly than those on Earth, but only by about 0.005 seconds. The National Air and Space Museum holds in its collection a Buzz Lightyear toy that flew aboard the ISS for 15 months in 2008 to 2009. Due to time dilation, Toy Buzz is approximately 0.015 seconds younger than would not have been without space travel. Toy Buzz may not have traveled as fast as Movie Buzz, but both were able to feel the effects of time dilation.

Buzz Lightyear toy on display at the DC Museum.

Although Earth’s orbit provides only a tiny difference in time, not enough for a human to notice, even at this speed, time dilation is of practical importance. When you use GPS to determine your location, you rely on a system of satellites orbiting the Earth. Your GPS calculates the time it takes to receive signals from each of the satellites, which it then uses to determine how far away you are from each. With this information, the GPS can compare these distances and calculate its position. Global positioning satellites are equipped with extremely precise clocks to increase the accuracy of its relayed positioning. However, due to time dilation, these clocks do not match the clocks on Earth. To avoid timing differences of a few nanoseconds, which could lead to positioning errors of hundreds of feet, these satellites must account for time dilation. While we may not yet be able to travel at the super fast speeds required for time dilation to jump us years into the future, our understanding of time dilation is making the convenience of GPS a reality.