I started wondering about this after solving a problem on the exam. Here is the problem: 2 planes has a speed v1 and v2. They are flying from the airport at the same time. The difference between their landings on the same airport is t. Express the distance between the airports as functions of v1, v2 and t. This is what I got: distance= v1v2t/|v1-v2| If this formula for the distance between the airports allways applies and we have defined positive and negative velocities as oposite directions when the problem is 1 dimensional, we get a negative distance if the planes goes in oposite directions and lands on the same airport after a time t. So here is my question: May there be such a mystic thing as negative distance so that 2 planes can go in oposite directions and land on the same place after a finite amount of time? Could this be something physical, not observed in our universe, but still real in other strange universes and extremly hard for us to imagine?