Time dilation is a phenomenon predicted by Einstein's theory of special relativity, which states that time can appear to pass differently for objects in motion relative to each other. Time dilation occurs when an object moves at speeds close to the speed of light.
In the context of astronauts traveling near or at light speed, as depicted in the movie Interstellar, time dilation would indeed occur. The theory of special relativity predicts that as an object's velocity approaches the speed of light, time appears to slow down for that object relative to a stationary observer.
In the movie, the astronauts embark on a space voyage near a supermassive black hole, where they experience significant time dilation. The intense gravitational field of the black hole causes spacetime to be highly curved, amplifying the effects of time dilation.
As the astronauts venture closer to the black hole or travel at high velocities, their clocks tick at a slower rate compared to clocks on Earth or observers at rest. This means that time for the astronauts passes more slowly than it does for observers who are not subject to such extreme conditions.
Consequently, when the astronauts return from their journey, they would find that much more time has passed on Earth compared to the duration they experienced. This effect is commonly referred to as "time dilation," where time appears to move more slowly for objects in motion relative to an observer in a different frame of reference.
While the depiction in Interstellar has some artistic liberties, it captures the essence of time dilation near massive objects or at high speeds. However, it's important to note that achieving velocities close to the speed of light is currently beyond our technological capabilities, and the effects of time dilation would be extremely small for any speeds we can currently achieve.