There are five ghost pirate ships drifting on an infinite ocean in the spiritual realm. Each ship moves at a constant speed and never changes direction. No two ships are traveling in parallel paths.
These ships have been drifting for a very long time. In fact, time extends infinitely both to the future and the past, and these ships have drifted for all of history.
Because they are ghosts, two pirate ships can pass right through one another. However, such collisions release a huge amount of spiritual energy. For every pair of ships that collide, one trillion souls are destroyed. Since the there are only 10 trillion souls in the universe, these ships could destroy all life if every pair of them collided!
Eight pairs of ships have already collided: are the 2 trillion remaining souls doomed?
Think of the ships as point masses. If 4 ships meet at the same time, this would destroy 6 million souls, since 6 pairs of ships collided.