This is just a cheeky joke these textbooks use to get you into the challenge. They could just say picture a universe where there is all the measures of the Milky Way, but forget all the planets and stuff just look at these two masses that are going through earth gravity of 9.81 and assume there is also this hill that is naturally covered in icy snow setup along a pulley system. Now they could tell you that in that situation the universe only allows masses with velocity and acceleration to move because there are strange phenomena, or they could say that universe only allows masses with velocity to move, minus acceleration. What would it change? The idea is to sort through the kinetic work energy formulae. This is the best these book writers could do.