There is another which states that this has already happened."
With the passing of the late lamented Douglas Adams, we will probably never have a definitive answer about what is the Ultimate Question of Life, the Universe, and Everything. We probably never were going to get one, anyway. However, it's my opinion that Adams telegraphed what the question was in the books. He never comes out and says it, and he never makes it definitive, because it's supposed to be a mystery, that's part of the point. But I think he decided what it was, and then, he couldn't help but slip it into the books, but in a way that allowed him plausible deniability, and allowed us to argue about what the real Question was.
No, it's not "What is six times nine?" While there's no particular explanation other than coincidence, improbability, and the various forms fate takes in the books, it's also clear that it's not quite right. And no, it's not "How many roads must a man walk down?" That's just PR.
There's only one being who claims definitively to know what the Question is, and that's Marvin. He insists he can read it in Arthur's brainwaves, and from other things he does, it seems plain he probably can do things like that. And why would he lie? "Life's bad enough without making up any more of it." And it's entirely appropriate to Marvin's character that he would be the one to know it.
The Ultimate Question comes up a few times in the books, each time apparently with no obvious significance to it, and each time, it seems kind of out of place, like it was kind of shoved in. By the author, that is. Except in one place, Marvin is a little more overt, though again, in a way that allows the author complete deniability.
"...I am at a rough estimate thirty billion times more intelligent than you. Let me give you an example. Think of a number, any number."If you stop to think about it, this is a very good candidate for the Ultimate Question. If you knew why the Answer, the only correct Answer, to the question "Think of a number, any number," should be Forty-Two, and why any other number is wrong, then surely you would have to understand something fundamental about the universe that eludes the grasp of everyone else.
"Er, five," said the mattress.
"Wrong," said Marvin. "You see?"
The mattress was much impressed by this and realized that it was in the presence of a not unremarkable mind.
And since Marvin knows both the Question and the Answer, clearly the universe has already been replaced with something more bizarre and inexplicable. Which goes a long way to explaining the rest of the books.
Last year I re-read the entire series and became even more convinced that this is the Question that Douglas Adams had in mind, and that he left subtle clues and hints in a few places so that once you found it you could be sure it was right. But I didn't have the foresight to take notes about those clues and hints, and now, I can't spare the time to dig through the entire series to find them. Pity, because other times I've shared this idea with other people, few found it convincing. And even fewer took the time to go through the book to test the theory. But they're in there, really they are. And no other candidate Question holds up nearly as well.
Maybe someday some note or letter Adams wrote will be found and we'll finally be sure. I could believe he might have some encrypted, encoded file left hidden somewhere for us to find; he seems the type. Then again, he also seems the type to appreciate the idea of a mystery never, ever solved for certain.