The twin paradox, discussed earlier, is a classic “paradox” in relativity. Another classic “paradox” is as follows. Suppose a runner moving at 0.75c carries a horizontal pole 15 m long toward a barn that is 10 m long. The barn has front and rear doors that are initially open. An observer on the ground can instantly and simultaneously close and open the two doorsby remote control. When the runner and the pole are inside the barn, the ground observer closes and then immediately opens both doors so that the runner and pole are momentarily captured inside the barn and then proceed to exit the barn from the back doorway. Do both the runner and the ground observer agree that the runner makes it safely through the barn?

The twin paradox, discussed earlier, is a classic “paradox” in relativity. Another classic “paradox” is as follows. Suppose a runner moving at 0.75c carries a horizontal pole 15 m long toward a barn that is 10 m long. The barn has front and rear doors that are initially open. An observer on the ground can instantly and simultaneously close and open the two doorsby remote control. When the runner and the pole are inside the barn, the ground observer closes and then immediately opens both doors so that the runner and pole are momentarily captured inside the barn and then proceed to exit the barn from the back doorway. Do both the runner and the ground observer agree that the runner makes it safely through the barn?