How does gravity affect the passage of time? (Image credit: Yuichiro Chino via Getty Images)
Einstein’s theory of general relativity upended humanity’s understanding of the universe more than a century ago, and since then, scientists have discovered that the steady march of time is anything but steady. Among the haunting implications of general relativity is that time passes more quickly at the top of every staircase in the world than it does at the bottom.
This mind-bending phenomenon happens because the closer an object is to Earth, the stronger the impacts of gravity are. And because general relativity describes gravity as the warping of space and time, time itself travels more slowly at higher altitudes and greater distances from Earth, where gravity has less of an effect.
So, if time is linked to gravity, does that mean that people on top of mountains age faster than people at sea level do? Does increased gravity actually make people age more slowly?
Indeed, for all objects farther away from a gravitational field, such as Earth, time actually moves more slowly, James Chin-wen Chou (opens in new tab), a physicist at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, told Live Science in an email. That means people who live at high altitudes age a tad faster than those plodding through space-time at sea level.
“Gravity makes us age slower, in a relative term,” Chou said. “Compared to someone not near any massive object, we are aging more slowly by a very tiny amount. In fact, for that someone, the whole world around us evolves more slowly under the effect of gravity.”
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The differences are minor but measurable. If you were to sit at the peak of Mount Everest — which is 29,000 feet (8,848 meters) above sea level — for 30 years, you would be 0.91 millisecond older than if you had spent those same 30 years at sea level, according to NIST (opens in new tab). Similarly, if twins living at sea level were to part ways for 30 years, with one relocating to mile-high (1,600 m) Boulder, Colorado, and the other staying put, the high-elevation twin would be 0.17 millisecond older than their twin when they reunited.
In a striking experiment, NIST researchers used one of the most precise atomic clocks in the world to demonstrate that time runs faster even a mere 0.008 inch (0.2 millimeter) above the Earth’s surface.
“These aren’t just calculations,” said Tobias Bothwell (opens in new tab), a physicist at NIST and co-author of a 2022 paper published in the journal Nature (opens in new tab) describing the experiment. “We have seen the change in the ticking of a clock at a distance roughly the width of a human hair,” he told Live Science.
The key to understanding why massive objects warp the passage of time is recognizing that “space-time” is a four-dimensional tapestry woven from three space coordinates (up/down, right/left and forward/back) and one time coordinate (past/future). Gravity, in a relativistic model, is what we call it when any object with mass distorts that tapestry, curving space and time as one.
“Anything that possesses mass affects space-time,” Andrew Norton (opens in new tab), a professor of astrophysics at The Open University in the U.K., told Live Science in an email. In the vicinity of an object with mass, “space-time is distorted, resulting in the bending of space and the dilation of time.
“The effect is real and measurable but negligible in everyday situations,” Norton said.
When it comes to non-everyday situations, however, this phenomenon — also known as gravitational time dilation — can get messy. According to Norton, GPS satellites circling the globe at an altitude of 12,544 miles (20,186 kilometers) need to adjust for the fact that their clocks run 45.7 microseconds faster than clocks down here, over the course of 24 hours.
“The most pressing effect of relativity over the passage of time is probably the accuracy of GPS,” Chou said. “Because they [GPS satellites] are moving at high speeds and high up away from the earth, the relativistic effects from speed and gravity need to be carefully accounted for so that we are able to infer our position on the globe with high accuracy.”
Closer to home, it is clear that gravity does, in fact, make us age more slowly. Sure, it’s usually only a matter of milliseconds, and cowering at sea level is hardly a viable anti-aging strategy. But time is both precious and fleeting, especially when distant from any objects with mass.