Time dilation

Time dilation is caused by differences in either relative velocity or gravitational field strength, as proven by Einstein's theories of relativity. If an object moves incredibly fast or sits near a massive gravitational body, its time will pass slower relative to an outside observer.

The twin paradox is a thought experiment where one twin travels in a high-speed rocket to a distant star while the other remains on Earth. Upon returning, the traveling twin is physically younger than the Earth-bound twin due to the effects of velocity time dilation.

Yes, Global Positioning System satellites experience both velocity and gravitational time dilation simultaneously. Their onboard atomic clocks must be deliberately adjusted by about 38 microseconds per day, or the entire navigation system would fail within minutes.

According to special relativity, as an object approaches the speed of light, its time effectively stops relative to outside observers, making time travel impossible. Furthermore, accelerating any mass to the speed of light would require infinite energy, which is physically impossible.