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CronoDAS comments on Rationality: Appreciating Cognitive Algorithms - LessWrong
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Comments (134)
That's a better explanation than I could come up with.
On a completely irrelevant note, why is "the sky is blue" the standard for "obviously true fact"? The sky is black about half the time, and it's pretty common for it to be white, too.
If you count navy as blue rather than as black, that happens more rarely than “half the time”. (I'd say “10% of the time” as I have that number cached in my mind as the duty cycle of fluorescence detectors for ultra-high-energy cosmic rays.) You know, the moon.
And when that happens, in places where electric lighting is widely used, it tends to become orange (not quite -- does that colour have a name?) during the night!
I believe CronoDAS was referring to overcast days when they said the sky is sometimes white.
Yes, I was talking about his claim that “the sky is black about half the time”; I didn't touch his claim that “it's pretty common for it to be white”.
EDIT: Okay, failed reading comprehension of my own comment.
It's something that everybody has quick access to. Another version would be "things fall", which is better but also only works on a planet and with objects denser than air for example. It would be ideal to have some unchanging reference object that we can make statements about, instead we have something that everyone has seen and they can say "I have seen that, it was pretty much blue"
That it's hard to come up with an "obviously true fact" that is in fact true without qualifications is itself interesting.
When the sky is white, it's not the sky; it's clouds blocking the sky. When the sky is black it's just too dark to see the sky. At least that was my intuition before I knew that the sky wasn't some conventionally blue object. I guess its a question of word usage whether the projective meaning of "blue" which is something like "looks blue under good lighting conditions" should still be applied when it's not caused by reflectance. Though it's not blue from all directions is it?
I would consider the clouds part of the sky, like the air, or the stars.
I'd say “sky” is a relative concept and depends on where you are. If I was on the mountainside and had clouds below me, I still wouldn't say I'm in the sky. (But I would if I was on a plane, so it's not as simple as “anything that's above me”.)
And I'm on the ground right now. There doesn't seem to be any clouds above me, but if there were, they'd be in the sky, and the sky would have white splotches.
I consider anything that is contiguously attached to the planet (or moon) which I am currently on (e.g. a man on a mountaintop), or less than about two metres from the ground (e.g. a man jumping up and down) to not be in the sky. Anything further than that from ground surface, and either currently ascending or able to maintain that altitude, counts as 'in the sky'; anything further than that from ground surface and not able to maintain that altitude, counts as 'falling from the sky'.
If I jump out of a second-floor window, I'm certainly falling, but I'm hardly falling from the sky.
The building is contiguously attached to the ground (unless it's some sort of flying building). You need to be more than two metres away from it and falling to count as 'falling from the sky'.
For safety reasons, it's probably also better to throw an object - I'd suggest a tennis ball - if you actually want to perform an experiment. You could get it to the state 'falling from the sky' by throwing it hard enough horizontally from a fourth- or fifth-floor window, or dropping it off a bridge.
Hmmm... I may need to update my definition to consider the 'dropped-from-a-bridge' case.
I'd say that it has to be far enough from the ground that you wouldn't notice the parallax effect if you walked around below it, it has to be above the horizon. Also, it can't be an airplane or something. I'm not sure why exactly that last rule is there, given that meteors and such count. Maybe most people would consider it part of the sky. I'd say it's in the sky, but not part of it.
What would you call a glass absorbing red/orange/yellow light and letting the rest through?
As I understand it, the sky does let red-yellow light through. It scatters blue light and lets red light through relatively unchanged. So it looks red-yellow near the light source and blue everywhere else.
Yes.