phrases - “Sir,' I said to the universe, 'I exist.' 'That ...

This answer focuses exclusively on the widespread attribution of the "'Sir,' I said to the universe, 'I exist'" quotation to Douglas Adams. I recognize that this issue is tangential to the OP's question, but if it is indeed a false attribution, I think, it ought to be exploded if possible.

As IQAndreas and Henry note in comments beneath the poster's question, the quotation is not easy to find among the various hydra heads of The Hitchhiker's Guide. That is because Douglas Adams probably never wrote it. What he did write is interesting in its own right, and similar enough to be confused or merged with Stephen Crane's much earlier statement in "A Man Said to the Universe"—especially if the person doing the confusing and merging is operating from memory rather than from either original text. From Douglas Adams, The Hitchhiker's Guide to the Galaxy: Original Radio Scripts, Fit the First (as originally broadcast in 1978):

NARRATOR: The Babel Fish is small, yellow, leechlike, and probably the oddest thing in the Universe. It feeds on brainwave energy, absorbing all unconscious frequencies and then excreting telepathically a matrix formed from the conscious frequencies and nerve signals picked up from the speech centres of the brain; the practical upshot of which is that if you stick one in your ear you can instantly understand anything said to you in any form of language—the speech you hear decodes the brainwave matrix. Now it is such a bizarrely improbable coincidence that anything so mindbogglingly useful could evolve purely by chance that some thinkers have chosen to see it as a final clinching proof of the non-existence of God.

The argument goes something like this:

'I refuse to prove that I exist' says God, 'for proof denies faith, and without faith I am nothing'. 'But', says Man, 'the Babel Fish is a dead giveaway, isn't it? It proves you exist, and so therefore you don't. QED'. 'Oh dear,' says God, 'I hadn't thought of that' and promptly vanishes in a puff of logic. 'Oh, that was easy' says Man, and for an encore he proves that black is white and gets killed on the next zebra crossing.

The odd thing here is that, rather than having a man tell the universe that he exists, Adams's quote has God telling Man that He refuses to prove His existence. Nevertheless, I suspect that the innocently fallible gods of the Internet managed to mash up a seriously flawed memory of Adams's quote with a slightly flawed memory of Crane's quote—and then attributed the result to Adams.

The tell-tale sign of false attribution of a quotation, obviously, is that no one can find the quoted wording in situ in the supposed author's work. A Google Books search has this problem with "'Sir,' I said to the universe, 'I exist.'" The only two books that find the phrase at all—Richard Rapson, Amazed by Life: Confessions of a Non-religious Believer (2003) and James Houston, The Fulfillment: Pursuing True Happiness (2007)—attribute it to Crane, evidently without looking up Crane's poem to get the correct wording. Rapson is quite free (and flat) with his quotation:

This, despite Stephen Cranes dismaying ditty: “'Sir, I said to the Universe/ I exist.'/ Said the Universe to me/ 'That is of no interest to me.'"

And Houston's epigraph from Crane omits the crucial word not from the already-unfaithful-to-the-original wording:

“Sir,” I said to the universe, “I exist.” “However,” replied the universe, “that fact has created in me a sense of obligation." —Stephen Crane

None of the books in the Google Books database (which includes a number of editions of The Hitchhiker's Guide) claim the phrase as Adams's.