I spent this weekend fielding a lot of questions from teenagers about how long it would take to get to various destinations in the solar system, with the general assumption being that if we simply strapped a bigger engine to a spaceship we’d get there faster. This is broadly true but I didn’t have the time (and their brains were too small) for me to explain all the nuances of the situation to them, so I’m just going to explain it to you instead. Lucky you.