It's already arguably ridiculous, but it gets stranger. The tesseract was created by humans in the future who've learned to manipulate time. They know Coop saved humanity by shoving books off his daughter's bookshelf and manipulating the hands on her old watch to play Morse code, so they built him a way to do that. It seems they couldn't build him a chalkboard or a fax machine, because the time in Interstellar is a closed loop -- which we think means it all happens concurrently and the tesseract was always there. So bad news if you were hoping for a movie in which he shoved the wrong book and historically rewrote his daughter to be a Hitler dinosaur.
Oh shit, that would have been a fun Act III.
We should have said this way earlier, but spoiler alert: Coop succeeds and his daughter uses those calculations to build a big-ass space colony and escape a shitty, dusty Earth. All it took was incredible luck and who knows how much time of Matthew McConaughey adjusting a watch!
So let's move past how incredibly inefficient dusty watch code is, and how Coop definitely would have gone mad before finishing. Why the shit didn't these future humans, who can build a time-traveling tesseract, not just hop in there and perform the calculations themselves? It seems like that adding "book poking robot" to a machine that spans the infinite timelines of dusty bookshelves wouldn't have been an impossible task for their development team.
"Hey Coop, how are you going to represent exponents with Morse code? And Greek letters? And math signs? And calculus symbols?"
Why even build humanity's only hope into a random-ass black hole and count on Matthew McConaughey to fall into it and volunteer for the most boring job in the universe? Those dick future people could have easily sent the message themselves, and to a time long before everyone on Earth was starving to death and choking on toxic ash. We don't know all the details about gravimetric chrono science, but we do know if you can build a time machine in the center of a black hole, you can probably send some spaceship plans back to Earth before everything sucked. And you can form a scheme that doesn't involve subjecting an astronaut to Data Entry Space Hell.