Ask HN: What is your favorite thought experiment?

Not so much a thought experiment - but trying to grasp the Library of Babel.

Somewhere on the pages is your entire life story, already written. Waiting to be discovered. The story of your birth, every variation of death. Every success. Every failure.

Just a meaningless collection of words waiting to be discovered, only given meaning once found.

https://libraryofbabel.info/

Even my post already existed: https://libraryofbabel.info/bookmark.cgi?vdayie_ifpawv163

Personally, I think Newcomb's Paradox is really interesting: https://en.wikipedia.org/wiki/Newcomb%27s_paradox

Einstein's thought experiment on simultaneity illustrated with a train (simultaneous, https://en.wikipedia.org/wiki/File:Traincar_Relativity1.svg), (not simultaneous, https://en.wikipedia.org/wiki/File:Traincar_Relativity2.svg)

This is meditative and not scientific, but still a thought experiment: To consider, who am I between two thoughts?

What is the one thing that could reverse an entrenched system, and how could you build a prototype in the least amount of time. Preferably, something people think is too much work, while it actually takes two days.

Imagine Pinocchio at rest.

Suddenly, Pinocchio says "My nose is growing!"

What happens next?