According to the theory of relativity, as an object approaches the speed of light, time dilation occurs. This means that time appears to pass more slowly for the moving object relative to a stationary observer. Therefore, if humans were able to travel at the speed of light, their clocks would appear to run slower relative to clocks on Earth from the perspective of an observer on Earth.
This phenomenon is known as "time dilation." It arises due to the interplay between space and time, as described by Einstein's theory of special relativity. Time dilation occurs because, as an object accelerates and approaches the speed of light, the flow of time for that object slows down relative to an observer who is not moving at such high speeds.
From the perspective of the travelers on a spaceship traveling at the speed of light, time would appear to pass normally for them. However, when they return to Earth or compare their clocks with clocks on Earth, they would find that less time has passed for them compared to the time that has passed on Earth.
This effect becomes more pronounced as the speed of the object approaches the speed of light. At speeds significantly below the speed of light, such as those achievable with current technology, the time dilation effects are negligible. However, for speeds close to the speed of light, time dilation becomes significant and has been observed and measured in experiments with high-speed particles.
It's important to note that traveling at the speed of light is currently not possible for objects with mass, according to our current understanding of physics. The concept of time dilation at the speed of light is theoretical and based on the predictions of special relativity.