How does interrupting Kubla Khan save humanity?

Question

In the finale of Dirk Gently's Holistic Detective Agency, the protagonists release the Salaxalan ghost (in Wenton-Weakes' body) in the primordial past, to go fix his ship, when they realize this will doom humanity.

Their solution is to go interrupt Coleridge's composition of Kubla Khan -- which in the story is a poem based on the ghost's story, explanation, and request for help.

How does this stop Wenton-Weakes and the ghost from fixing their ship?

It clearly doesn't stop the ghost from possessing Wenton-Weakes, or from being released in the past (the protagonists say there are now two ghosts - the original one, and now also the one that returned to the past, and has been stuck there another eternity). And, of course, the change to the poem is billions of years later than the change-point where the ghost tries to fix the ship.

(The book's prologue offers a clue - a visual that, in retrospect, we understand as some version of the ghost, crying in anguish at Coleridge being interrupted. But that's not very clear either.)

Answer 1

It seems a bit unclear. In the author's own words:

Ahem. All I can say is that it was as clear as day to me when I wrote it and now I can't figure it out myself. Sorry about that.

Later on that discussion thread someone quotes from an FAQ written on an alt.fan site:

In the book, Kubla Khan has a second part. The book is not actually set in our existence. It is set in an existence in which the second part of Kubla Khan exists. This second part of the poem tells the ghost about the existence of the time machine and how to travel back and stop the ship from exploding. As we well know the explosion of the ship is what caused life to begin on this miserable little planet of ours. When Dirk and Reg realised this they simply went forward in time to when Coleridge was writing the second part of Kubla Khan and stopped him. Dirk just interrupted him and talked so much that Coleridge forgot what the second part was going to be about and therefore could not finish it! This change of history sent reality back into our perspective and the human race lived on (Yay, yippee!).

That in and of itself doesn't quite make sense to me either but here is what I figure.

First, as for the change in the poem happening billions of years after the ghost heads back to the ship, Adams seems to be following a sort of time-travel "synchronicity" logic which says if someone goes back to the past and takes 1 hour to change things, you have 1 hour to do things in that continuum (no matter where in time you are) until the change happens. From Chapter 34:

"How long," said Dirk, quite calmly, "would you guess that it's going to take that fat self-deluding bastard to reach his ship? Because that's how long we have.

This chapter ends with them trying to figure out what to do and a book (which is surely the Coleridge anthology that Michael took out earlier) falling out of Michael's discarded jacket. This causes them to realize they need to stop Coleridge from completing Kubla Khan. Since we don't actually get to see the second part of Kubla Khan, it seems hard to say exactly why this is, but here are two guesses:

• The second part of Kubla Khan contains the key to building the time machine, so this interruption prevents the ghost from going back in time. This would explain why the time-travel device no longer works at the end.

• The second part of Kubla Khan is what makes Michael sympathetic to the ghost's story. This POV is espoused in this SFF answer.

Answer 2

Thanks for your good ideas. I have another one, spontaneously adding some of your hints:

I imagined that the ghost was still inside of Coleridge while Gently came by. During his stay in Coleridge's house he hypnotised the ghost. The ghost didn't know Gently yet, so he would not get suspicious. He gave him some confusing thing or corrupting action to think of or to do at the time it would be at him to destroy humanity (he told Coleridge, AND the ghost it's not a meteor but an albatross to think of. I'd say here symbolically meteor means doom and the albatross means hope). About Gently saying they would not have much time to react, I think by leaving that place within these few minutes via the time machine, again they had time "forever", since they then took action to prevent the ghost from being successful. The ghost had already been hypnotised in the past so they could let him go within Martin's body. I didn't notice about the book dropping out Martin's discarded jacket. It helps with my theory: the book itself would contain the trigger words for the ghost for the hypnotic order to be executed. But there is a problem: the book MUST NOT have been instantly, "miraculously" changed by this activity (like the way things would change in the move back to the future) but already contain the trigger within their reality, otherwise the hypnosis would NOT affect the ghost walking towards the ship.) This way of manipulating time is contradicting to the fact, that in the end surprisingly, "miraculously" Bach's music exists. Probably the time machine is intelligent enough to change reality either the one or the other way. One could even figure further on, by this kind of manipulation the machine got damaged.

I enjoyed the thought they would put the fate of humanity into this high risk activity. Also, this is one really great detective story where you have to find the ultimate clue by yourself :) to me it is a lovely even caring and genius trick by the author towards the reader.

Answer 3

I also thought that perhaps that the ghost's mind is so fractured from loneliness and age that, like Professor Chronotus, he needs written reminders of events; in this case, the exact circumstances that played out to cause the accident. And this reminder is written into the second part of the poem, so with that jotted down reminder gone, the ghost is at a loss to remember why the ship blew up at all.