science

They're talking about time dilation.

Objects with no mass traveling at light speed in a vacuum don't experience time.

A photon, traveling through a vacuum for forty years, from its perspective, leaves the instant it arrives.

Likewise, if you can travel at the speed of light for forty years and came back to earth, your twin would age forty years and you wouldn't age at all.

At a much smaller scale we have to use time dilation to keep clocks in space running at the same time as clocks on Earth. Because in geosynchronous orbit they are traveling faster than objects on the ground.