The phenomenon of time dilation due to relative velocity causes astronauts on the International Space Station (ISS) to age slightly slower by a few milliseconds.
Astronauts Butch Wilmore and Suni Williams are stranded on the International Space Station (ISS) until February 2025 due to an incident with a Boeing spacecraft, but this situation isn’t entirely detrimental. In addition to witnessing the magnificent Earth from space, they are also aging slower compared to people on the ground.
Astronaut Matthias Maurer of the European Space Agency (ESA) conducts a spacewalk outside the International Space Station (ISS). (Photo: NASA).
This difference is not easily noticeable. After six months living on the ISS, astronauts age approximately 0.005 seconds slower than those on Earth. Thus, after about nine months in space, Williams and Wilmore will be about 0.0075 seconds younger than if they returned to Earth in June 2024 as originally planned. There are scientific reasons behind this phenomenon, beginning with Einstein’s theory of relativity.
Time Dilation Due to Gravity
According to Einstein’s theory of relativity, space and time combine to form a structure that pervades the universe: spacetime. Spacetime is not flat but curved and can be distorted by mass and energy. This effect leads to the phenomenon of time dilation due to gravity: Time appears to flow slower near a massive object because the object’s gravity bends spacetime.
This means that a clock worn on the ankle will gradually run slower compared to a clock worn on the wrist because the ankle is closer to the center of the Earth’s gravitational pull. However, this effect is too small for humans to perceive.
Astronauts on the ISS are about 418 kilometers farther from the center of Earth’s gravity than an average person. However, astronauts age slower due to another phenomenon: time dilation due to relative velocity.
The gravity of Earth bends spacetime. (Photo: Design Cells).
Time Dilation Due to Relative Velocity
Time dilation due to relative velocity means that time flows slower for someone moving at high speeds. Consider a pair of twins, one in a spaceship traveling near the speed of light while the other remains on Earth. Upon returning, the space traveler has aged only a few years, while the twin on Earth has aged several decades.
No one has conducted this experiment in reality, but there is supporting evidence. Scientists once launched an atomic clock into orbit and brought it back while keeping an identical clock on Earth. The result showed that the orbital clock ran slightly slower than its “twin” on the ground. Astronauts on the ISS experience a similar effect.
The ISS orbits Earth at about 8 kilometers per second (29,000 kilometers per hour), according to NASA. This means that time for the astronauts flows slower compared to people on the ground. For astronauts, the effect of time dilation due to velocity is more significant than gravitational time dilation. Thus, they age slightly slower while in space.
Astronaut Telomeres Lengthen in Space
Another strange phenomenon that astronauts experience may also contribute to anti-aging. Some recent preliminary studies indicate that the telomeres of astronauts elongate while in space. Telomeres are caps at the end of chromosomes that help protect against damage. As people age, telomeres shorten.
However, after astronaut Scott Kelly spent a year in space, he returned to Earth with longer telomeres than when he left. The same occurred with four commercial astronauts during SpaceX’s Inspiration4 flight in 2021, despite their space experience lasting only three days.
Nevertheless, experts are currently unclear whether longer telomeres correlate with increased longevity. They are continuing to research this issue.
Moreover, aging slower by a few milliseconds due to spacetime factors will not create a significant difference. This is not the primary reason for humans to venture into space. According to NASA, space exploration helps unite the world to inspire future generations, leading to groundbreaking discoveries and creating new opportunities.
