According to the principles of special relativity, if one person travels at twice the speed of another person, they will cover more distance in the same amount of time as observed by an outside observer who is at rest relative to the two individuals.
This effect is known as the time dilation and length contraction. When an object is in motion relative to an observer, time appears to pass slower for that object. Simultaneously, the length of the object in the direction of motion appears to contract or shrink from the perspective of the observer. These effects are reciprocal, meaning they occur for both observers relative to each other.
So, if one person is moving at twice the speed of another person, the moving person's time appears to pass slower according to the stationary observer. Consequently, in the stationary observer's frame of reference, the moving person will cover more distance in the same amount of time compared to the stationary person.
It's important to note that this effect is only perceived from an outside observer's perspective. For the individuals themselves, their own sense of time and distance remains constant. It is the comparison between two observers in relative motion that reveals these effects.