What are your favorite thought experiments?

Oh man, there are so many. I love a good thought experiment.

Hilbert’s Hotel, showing how counterintuitive infinity can be.

The Ross-Littlewood paradox, in which you add nine balls to a vase an infinite number of times and end up with an empty vase.

The St. Petersburg paradox in which seemingly simple and correct application of probability theory results in a wildly incorrect answer.

The Chinese Room; although I strongly disagree with Searle’s analysis of it, it’s still an interesting argument and requires some thought to refute.

Nitpick: a 60 million digit number divided by 1 billion is not 51 million digits, instead, it would be ≈ (60 million - 9) digits ≈ 59,999,991 digits long.

That would be true if the monkey’s keypresses were statistically random, in that each key would have the same probability of being pressed as any other key, but my personal hunch is that a monkey banging away on a keyboard is not statistically random and thus they would never achieve this goal.

Heck, I’d bet that if a human pounded “randomly” on a keyboard, and the resulting characters were converted into their ASCII binary equivalents and then run through the Diehard statistical test suite, they’d fail those tests miserably.

Good catch, thanks. My math had erroneously slashed my gigantic number by about 1/6, but your correction shows how big the number really is; dividing by a billion is barely noticeable.

I recently learned about Roko’s Basilisk, probably from this board. It’s like a cross between Pascal’s Wager, The Ring, and The Matrix. Good stuff.

As long as there is some nonzero probability of hitting every key, the monkey would eventually produce Hamlet. It might just take longer than if the probability of each key were the same. In fact, there must be some nonuniform probability distribution that would produce Hamlet faster than if the keys were uniformly likely.

With a dash of I Have No Mouth, And I Must Scream.

I can’t believe I left that out of the description.

The scariest thing about Roko’s Basilisk is that allegedly Elon Musk and Grimes met while discussing it.

I’d also (and maybe more controversially) add I’m a fan of the Trolley Problem thought experiment, despite now being meme-fied to the point of being somewhat meaningless. I do think its actually a good thought experiment that highlights real complications in ethical systems.

I like Galileo’s thought experiment where he proved that heavy objects do not fall faster than light objects. Usually people think he dropped two stones from the tower of Pisa, a heavy one and a light one, and both dropped simultaneously. He probably never did that, and if he did, he did knowing the result. And he knew from thinking about it like this:
Start postulating that heavy objects fall faster than light ones. Take two objects, one heavy, one light, and bind them together with a slack rope. A rope transmits force by pulling but not by pushing. Let them fall. The heavy object falls faster, the light one lags behind. Until the rope is tight, when the total mass of both bodies falling increases, so they suddenly accelerate. Which is absurd, so heavy objects do not fall faster than light ones. QED.
I find this brilliantly visualized.

Yeah, after considering it some more, you’re absolutely right.

I must’ve been thinking along the lines of the monkey pressing multiple keys simultaneously with their palms, of which the probability distribution of consecutive keys would correspond to the monkey’s hand shape mapped onto the keyboard, implying certain keys would never follow each other because the other keys covered by that hand shape would interpose first.

On the other hand, if the monkey was pressing keys one at a time, then like you said as long as each key has a nonzero chance of being pressed, then Hamlet is inevitable.

A quantum physics thought experiment that I only half understand but it still seems fascinating: what happens when an observer is themselves in a superposition of states according to another observer? Wigner's friend - Wikipedia

Here is Bob Newhart’s take on that question.

https://www.youtube.com/watch?v=Ngmf8G5xKas

That was going to be my one. I’m a fairly strong Dennettist on the Chinese Room.

Also, the Mary the Colour Scientist one.

I’m a fan of the Gettier Problem, in part because its creator threw a wrench into thousands of years’ worth of epistemology with a single three-page article.

My favorite thought experiment: which would taste better, the cheesecake or the apple pie?