According to the theory of relativity, time dilation occurs when an object is moving at relativistic speeds. This means that time appears to slow down for objects that are moving relative to an observer. In the scenario described, the clock on the train would appear to be running slower than the identical clock held by the stationary observer. This is because the time on the moving clock is dilated due to the high velocity of the train, and the observer on the train would measure a shorter amount of time than the stationary observer.