Time dilation is a phenomenon predicted by the theory of relativity, specifically the special theory of relativity (STR). It refers to the difference in the passage of time between two observers in relative motion. Time dilation occurs when an object is moving at speeds comparable to the speed of light.
According to the special theory of relativity, as an object accelerates and approaches the speed of light, time appears to slow down for that object relative to a stationary observer. This means that clocks on the moving object will appear to run slower compared to the clocks of the stationary observer.
As an object's velocity increases, the effects of time dilation become more significant. The closer the object's speed is to the speed of light (299,792,458 meters per second in a vacuum), the more pronounced the time dilation effect becomes.
From the perspective of an observer on the moving object, time appears to flow normally. However, from the perspective of a stationary observer, time on the moving object appears to be moving slower.
For example, let's consider a scenario where two spaceships are involved: Spaceship A and Spaceship B. If Spaceship A is traveling at a significant fraction of the speed of light relative to Spaceship B, the astronauts on Spaceship A would experience time passing slower compared to the astronauts on Spaceship B. This means that, for the astronauts on Spaceship A, a shorter amount of time would elapse compared to the astronauts on Spaceship B, even though both initially synchronized their clocks.
This effect has been experimentally confirmed through various observations and measurements, including high-speed particle experiments and the operation of global positioning systems (GPS), which must account for time dilation due to satellites' velocities.
In summary, time dilation near the speed of light refers to the slowing down of time for an object in motion relative to a stationary observer. As an object's velocity approaches the speed of light, the time dilation effect becomes increasingly significant.