According to our current understanding of physics, it is not possible for an object with mass, such as a train or any material object, to travel at the speed of light. As an object with mass approaches the speed of light, its relativistic mass increases, requiring an infinite amount of energy to reach or exceed the speed of light.
However, let's imagine a hypothetical scenario where a train could somehow travel at the speed of light. In this case, according to the theory of special relativity, time dilation would occur. Time dilation means that time appears to pass more slowly for objects that are moving relative to an observer at rest.
From the perspective of an observer on the train, time would appear to pass normally. However, for an observer outside the train, time would appear to slow down as the train approaches the speed of light. This phenomenon is known as time dilation.
As for the passengers on the train, they would not experience any sensations related to the train's motion because, in their reference frame, they would perceive time passing normally. They would not feel any increase in their own mass or any significant changes in their physical experience. However, it's important to reiterate that this scenario is purely hypothetical, as objects with mass cannot actually reach or exceed the speed of light.