A while ago, the late humorist Douglas Adams told a joke in his best-selling book series: Civilization had amassed an enormously power computer called Deep Thought and tasked it to find the answer to the ultimate answer to Life, the Universe, and Everything. Deep Thought informed the anxious crowd that they would have to wait 7.5 million years for the answer. When the day finally arrives, Deep Thought reports that the Ultimate Answer is Forty-two, while pointing out that this answer is meaningless because they did not ask for the Ultimate Question.
When paired with the Ultimate Answer (42), the "Ultimate Question" should explain what the universe is for and why we are here.
Then a bunch of crazy plot stuff happens, but you'll have to read Adams' books for that.
What's of interest that the author establishes, through both narration and later through Prak—a character who knows all that is true—that it is impossible for both The Answer and The Question to be known in the same universe; should someone know both the question and the answer, the universe would cease to exist and would be replaced by something more bizarre and inexplicable. The narrator teases the reader that another theory states that this has already happened before.
Douglas Adams insisted that the number was meaningless. Fans continued to speculate elaborate theories for what sort of question could be so transcendent and also be answered by the number forty-two. Hey guys, he already gave us the question.
I posit that the Ultimate Question is, "How many times have the Ultimate Question and Ultimate Answer been known, and thusly the universe been eradicated and replaced by something more bizarre and inexplicable?"
My submission fits all the relevant criteria pulled from the literature and was provided by the author. It may not be the Question that Adams intended (nor do I suspect he ever intended to reveal one), but nonetheless it fits.