It was one suggested by Bryan Magee in relation with Kant's idealism, but it could apply to almost any strand of innatism.

He did not say this exactly, but the gist of it is on point. Take any object, say a red ball. You're in front of a red ball and you experience it. No problem. Now imagine losing sight. What do you have in front of you? A red ball still. You can touch, smell it, hear it bounce and so forth. But now eliminate touch. What do you say? It's still a red ball, you can hear it bounce and smell the rubber.

But now eliminate smell, sounds and taste, etc. What do you have in front of you? It's a problem. If you experienced the ball normally but then lose all senses one by one, you have to still conclude that there's something there. What is left of it though? Some kind of mental essence for us and a mysterious nature left for the object, both inscrutable to us.

And if a person happens to be born, missing all senses sadly. What world is there for that person?

It was a profound experience for me at the time and pointed to me to our quite fundamental epistemic situation. I've never ceased to be baffled by it, simple as it may be.

Thank you for this! I'm going to be thinking about this all day now.

People living a lot longer. There's a scientist who's betting there is already a person living among us who is going to reach 150 years old for sure. Currently, that person is in their 50s. Then, I'm thinking could we possibly also have a brain and health in proportion to that length of time? So that at 50 years of age, that person is literally only 25 physically.

Some people might think this talk about living longer is now cliche and serves nothing but personal selfish desire. However, if you think in terms of the length of time it takes for an invention, a phenomenon, or a breakthrough to come to fruition, you'd wish there's much more time. Some discoverer or inventor actually die without seeing the result of their genius.

Then, I'm thinking could we possibly also have a brain and health in proportion to that length of time? — Caldwell

I'd hope so. Cognitive facilities decline slowly as we age and if one were to live past 110 let's say, without some sort of medical/pharmacological intervention then I would imagine it wouldn't be very stimulating. But like you said, if there were some sort of medicine/technology that offset ones physiology with their mental "age", I agree we could see an increase in progress (optimistically speaking).

It’s known colloquially as the “Copernican Revolution”, although Kant never called it that. It’s found in the preface to the second edition of the first critique. Dunno about that Magee guy, but metaphysically-inclined folks been bashing or idolizing it since 1787.

Although, it’s not technically a thought experiment, per se, in that Kant theorizes as to the actual validity of the process it describes. So.....no physical science here, no Einstein or Schrodinger, but to some, every bit the paradigm shift in its field, as either of those in theirs.

A couple.

I'm sure this is a common one. It's blown my mind when I try to get my arms around it since I was a teenager. Still does. Imagine nothing. Really nothing. No one to know it's nothing. No space, not quantum vacuum. Nothing. Not anything anywhere. No things. No where.

I'll start the next one with one of my favorite quotes. If you've read many of my posts you've seen it before. I end up using it every week or so. From Franz Kafka:

It is not necessary that you leave the house. Remain at your table and listen. Do not even listen, only wait. Do not even wait, be wholly still and alone. The world will present itself to you for its unmasking, it can do no other, in ecstasy it will writhe at your feet.

In my thought experiment, I'm in a nondescript room. Say 10 feet by 15 feet. Concrete block walls painted beige. Linoleum flooring. Fiber ceiling tiles with low intensity inset lighting. Everything I remember from an elementary room classroom. No windows. A single door I've agreed not to open unless really necessary. There's a comfortable chair, a table, and paper and pencils. The air is comfortably warm. If you're wondering how I'd eat and pee and other science facts, just repeat to yourself "It's just a thought experiment, I should really just relax."

I am me, with all my memories and knowledge. I'm here on my own free will with no coercion. I'm looking forward to this. It's fun. My job while I'm here - create and describe the world just based on what I can observe in the room with no reference to anything outside the room or any understanding I have of the world outside.

I'm sure this is a common one. It's blown my mind when I try to get my arms around it since I was a teenager. Still does. Imagine nothing. Really nothing. No one to know it's nothing. No space, not quantum vacuum. Nothing. Not anything anywhere. No things. No where. — T Clark

Isn't this the thought that comes to mind when someone tries to think about how it was before birth for each of us? Speaking for myself, when I try to think of any concept at all: long, boring, slow, pain, happy or anything else, none of this applies to whatever before birth was. So I think we all have an inkling of this already.

I suppose the only "positive" thing I could say is that it was dark. Not in the sense of feeling in a bad mood or being in a bad place.

But maybe even that's not correct.

. I'm curious to see what Thought Experiments you guys find intriguing. — theUnexaminedMind

Zeno's paradoxes.

Simple. Classical. Still intriguing.

My favourite thought experiment? Making out with Pamela Lee Anderson. It's quite good, I assure you. Rather exciting.

Thank you everyone for your comments. They have lead to some interesting lines of research for me. :smile:

Isn't this the thought that comes to mind when someone tries to think about how it was before birth for each of us? — Manuel

I don't think they're the same, at least not for me. Mine is less personal. It's not that I don't exist. It's that nothing exists. But...but...but.... Blew my mind again.

Hmmm. But if nothing exists, doesn't that include me (you) as well?

Hmmm. But if nothing exists, doesn't that include me (you) as well? — Manuel

Of course, but me not existing is not hard to imagine. The idea that nothing could exist is.

Ah. Yes, it's mind boggling.

No space — T Clark

Well “space” means “there is nothing there”. So I’d think what you want to imagine is just a world with all objects taken out of it, plenty of space, but not much else. I don’t see much difficulty in that.

Now if you’re trying to imagine a world without space, idk if that makes sense or not but what’s the point of doing so?

But I don’t get the point of the second thought experiment at all. Ok, I’m isolated in a classroom and I must have drank way too much because I start saying things about describing the whole world using nothing but the contents of the room. Is it supposed to indicate that this is possible somehow? Or what exactly?

Well “space” means “there is nothing there”. So I’d think what you want to imagine is just a world with all objects taken out of it, plenty of space, but not much else. I don’t see much difficulty in that. — khaled

No. Space does not mean there is nothing. First off, space is something. It's expanding
. Second - physicists believe all of space is permeated by a quantum field.

But I don’t get the point of the second thought experiment at all. Ok, I’m isolated in a classroom and I must have drank way too much because I start saying things about describing the whole world using nothing but the contents of the room. — khaled

I was worried this might be ambiguous. When I said "the world" I meant the essence of reality, the thing philosophers are searching for. Ontology. That's the way Kafka was using the word. I should have been clearer.

One of my favorite thought experiments is the boy with no words. Suppose if a boy was raised his whole life without any sort of made up language of communication. How would he think? I think he would think in terms of images and feelings. The essence of what we think.

in terms of images and feelings. The essence of what we think. — Thinking

Essence of how we think. But that aside, it’s always been my contention that fundamentally, humans think in images and feelings. Tough sell, though, these days.

The universe as a library of all possible books.

The number of books about god must be atheist's sexual exploits with Pamela Anderson could not fit in our universe.

Nietzsche's Eternal Recurrence:

What if a demon were to creep after you one night, in your loneliest loneliness, and say, 'This life which you live must be lived by you once again and innumerable times more; and every pain and joy and thought and sigh must come again to you, all in the same sequence. The eternal hourglass will again and again be turned and you with it, dust of the dust!' Would you throw yourself down and gnash your teeth and curse that demon? Or would you answer, 'Never have I heard anything more divine'?

In this, I think that the answer of 'never have I head anything more divine' would be the ultimate expression of life affirmation. To want life in all of it's pain and joy, again and again and again. Would you not strive to live the best life you possibly can? So that you can re-live your best life, over and over again? Ties nicely into his overall philosophy of growth. Of becoming.

My all-time best thought experiment:

What if I "wake up" from a "dream" into the "real world" and then "wake up" to find myself in the "dream" that I thought I "woke up" from!

Before one studies Zen, mountains are mountains and waters are waters; after a first glimpse into the truth of Zen, mountains are no longer mountains and waters are no longer waters; after enlightenment, mountains are once again mountains and waters once again waters. — Dogen (Zen Master)

I think that the answer of 'never have I head anything more divine' would be the ultimate expression of life affirmation. — CountVictorClimacusIII

Absolutely. And there's that small bonus of sticking it to the demon.

Before one studies Zen, mountains are mountains and waters are waters; after a first glimpse into the truth of Zen, mountains are no longer mountains and waters are no longer waters; after enlightenment, mountains are once again mountains and waters once again waters. — Dogen (Zen Master)

There are layer to this that I need think to think on. But at first glance, I thought, if you had a teacher that told this to you, then knowing that the end result appears the same as it is to you know, why bother taking the journey? But then, what if there's wisdom to be gleamed from the journey itself, as we intuitively know from life. I like this one. Thanks,

I thought, if you had a teacher that told this to you, then knowing that the end result appears the same as it is to you know, why bother taking the journey? — theUnexaminedMind

Good point!

Can’t say it’s a favorite, and it’s certainly not upbeat, but it’s pith still stands out to me. A thought experiment in ethics:

Without your consent, you will be placed in a desolate place, say on the moon, where you’ll be estranged from all of humanity and thus live for all eternity, and this with an eternal view of Earth’s inhabitants, who, together with all your loved ones, will fully forget you as though you’d never existed. This predicament of yours could be created by gods, through the teleportation and other advanced sciences of aliens, by the magic of demons, it doesn’t matter. It just sets the stage for the thought experiment proper. Given this predicament, you are forced to make a choice between two alternatives. Either A) you will eternally suffer and, in return, the entirety of humanity (hence, including all loved ones) will live in a utopian bliss of peace, love, health, prosperity, wisdom, etc., for all eternity, with you being aware of this state of humanity throughout or, otherwise, B) you will yourself experience eternal bliss with the price being that the entirety of humanity (hence, including all loved ones) will unendingly suffer miserably, again with you being aware of this throughout.

If you choose the latter option, you won’t suffer any while watching all of your loved one’s suffer, but will instead find great pleasure in so watching. And if you choose the former, you will suffer in any number of ways despite your loved ones’ obtaining all the happiness you could ever wish for them to have and you being aware of this.

Which of these future realities do you choose for yourself?

If the thought experiment sounds childish, it’s because it was concocted by a teenager while he was contemplating the extremes of morality. Embarrassingly, yes, me. But, its immaturity aside, I still find the thought experiment poignant as regards which choice would be good and which bad, and for what reasons so. (Would one's reasons rely on moral relativism, moral idealism, something other?)

Simple. Classical. Still intriguing. — ssu

But you have to pretend calculus isn't a thing to fully appreciate them.

One of my favorite thought experiments is the boy with no words. Suppose if a boy was raised his whole life without any sort of made up language of communication. How would he think? I think he would think in terms of images and feelings. The essence of what we think. — Thinking

Like Kasper Hauser? An interesting thing about Hauser is that he didn't dream until he was taught language (around age 13 iirc).

I'm going to be boring and go with Rawls' veil of ignorance (aka how humans would think anyway if they weren't utter douchebags).

But you have to pretend calculus isn't a thing to fully appreciate them. — Kenosha Kid

On the contrary! That we have calculus and these thought experiments still show that we don't fully understand basically infinity (or it's interesting counterpart). Sure, we have calculus, but not a clear solution. That both Newton and Leibniz couldn't easily crack the infinitesimal in a way that we all refer is the interesting part. Yes, we have limits, we have even infinitesimals and basically infinity is taken as an axiom.

I think the basic problem is that we make counting, natural numbers, as the basis for all mathematics. A bit hard then to add there infinity or infinitesimals in that picture. When you think of it, that was basically the Eleatic School's counterargument. Unfortunately we don't have the book that Zeno wrote and the description of the Eleatic School comes from it's opponents, who didn't have on their agenda to make the Eleatic School's case.

I agree that calculus of limits is not an intuitive, everyday way of thinking, but it's pretty trivial to a mathematician and is the basis of most of physics. Or to put it another way, in the everyday experience of someone dealing with continuum kinematics, this isn't a headscratcher at all _now_. Historical interest is obviously different.

I might be wrong, but I think Math is so beautiful, that to a such essential part of mathematics, there perhaps is a simple intuitive and beautiful reasoning. Something that would easily tell us what is the link or "the catch" between natural numbers and the infinitesimal / limits. Of course many do think this is a total non-issue as there just is what we have been taught at school (and it works). From a philosophical viewpoint I beg to differ.

Still, for everyday use it's a no-brainer: the foundations of calculus and it's relationship to the foundations of mathematics isn't something that people much think about as obviously we have the correct answer how to do it.

I might be wrong, but I think Math is so beautiful, that to a such essential part of mathematics, there perhaps is a simple intuitive and beautiful reasoning — ssu

Cauchy and Weierstrass did just that. Cauchy: "When the values successively attributed to the same variable approach indefinitely a fixed value, eventually differing from it by as little as one could wish, that fixed value is called the limit of all the others."