The issue isn't that there's nothing new to learn. It's that the frontiers of science are at a point where it takes huge amounts of work and money to advance them any further. In physics, we need particle colliders whose prices are increasing without cease. In biology, we have to go to nastier and nastier places to discover new organisms. As the price goes up, we have to accept that many of the scientific questions we have posed are questions that will go unanswered for long amounts of time.