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Comment by throwaway738 | Hacker News Reader

The first 2 sentences of the article, literally:

"Mirror image is a tricky thing, but it's pretty clear when you look at words in a reflection, that mirrors flip things horizontally rather than vertically. Or, at least it seems that that's the case."

Majority of HN comments: "A mirror doesn't flip anything"

The "At least it seems that's the case" clearly suggests that there isn't an actual flip. But ask a regular person whether a mirror flips that is what they will say. The article addresses both the common wisdom and the actual science.

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Absolutely, this is a pretty solid explanation and HN (and similar places) always have the bizarre take on explaining of paradoxes to shout "It's not a paradox!" Paradoxes are about appearing, at first thought, to be impossible, not it being literally impossible. In this case, it's the two observations:

1) A mirror is rotationally symmetric so should treat left/right the same as up/down.

2) A piece of paper with writing held up to a mirror reads right-to-left instead of left-to-right. But it does not read bottom-to-top.

This asks for an explanation - one that the article gives. Why do so many here feel the need to say that since this has an explanation, it is not a paradox? Outside of fiction, every paradox has an explanation and, moreover, we're discussing an article that gives that explanation.

But: a mirror does flip something, it flips in-and-out. Mirror images are not the same.

The (perhaps overly) charitable take on "It's not a paradox!" responses is that it's something which didn't appear impossible or weird to that responder, and the article failed to make the case for why there's even something that needs an explanation.

I'm curious to know what percentage of commenters who know exactly how mirrors work can perform simple tasks like assembling a puzzle with the same speed only looking through a mirror.

I don't think that would prove anything at all, since knowing how something works doesn't mean you can use it in place of your usual behaviour. You also have to unlearn manipualting things in non-mirror space.

Smarter Every Day actually has a video demonstrating a similar thing: https://www.youtube.com/watch?v=MFzDaBzBlL0

I know how a blindfold works and I can’t assemble a puzzle with a blindfold on. Is that curious?

> Paradoxes are about appearing, at first thought, to be impossible, not it being literally impossible.

That's not true, or at least it's not the whole truth. Real paradoxes do exist: A barber shaves everyone who doesn't shave themselves, who shaves the barber?

So if true paradoxes do exist, it seems fair to call out alleged paradoxes for not truly being paradoxes.

> Real paradoxes do exist: A barber shaves everyone who doesn't shave themselves, who shaves the barber?

I'm clearly missing something but how is that a paradox?

Better paradox:

This statement is false.

If the barber doesn't shave himself, then he must shave himself because he shaves everyone who doesn't shave themselves. But he only shaves those that don't shave themselves, so he cannot shave himself....

https://en.wikipedia.org/wiki/Barber_paradox

Or there is a second barber and they shave each other? If there is only one barber then it is a paradox.

There is only one barber and he's not bald or otherwise excluded from the 'everybody' in "he shaves everybody who doesn't shave themselves." It's not a lateral thinking problem, or a matter of thinking outside the box. The scenario described is simply impossible. Everybody, including the barber, is either shaved by the barber or [XOR] shaves themselves, which is impossible in the case of the barber.

From your wikipedia link: The barber is the "one who shaves all those, and those only, who do not shave themselves". The question is, does the barber shave himself?

If the answer is "no", then he's shaved from another barber and the problem is solved. Nowhere is stated there's only one barber in the world.

Tattoo artists don't tatoo themselves but they're not living paradoxes. How is this different?

Again, I'm sorry for the obvious elephant in the room I keep missing.

EDIT: I see your answer to sumtechguy, I understand now it's more metaphorical than pratical. In my understanding, the paradox seems to arise when you try to put all your existing elements to fit one of 2 kind of boxes, which are clearly not enough.

Parent poster forgot a critical condition for it to be a paradox. As they stated it's not, a second barber could shave both themself and the first barber.

The paradoxical statement would be "A barber shaves all those, and only those, who do not shave themselves. Who shaves the barber?" Without the second condition (only those who don't shave themselves) it's non-paradoxical.

Replace 'A' with 'The' and it works. Tbh I assumed people were already familiar with the Barber Paradox and didn't word it defensively, but if you take 'a barber' as referring to a specific barber then it's a paradox.

Show me such a barber and I'll agree that they exist.

The paradox exists and consequently, the barber cannot.

Right, the mirror doesn't actually flip. It's just we think about turning around to try to "match" what we see.

And humans are more left-right symmetric than up-down symettric.

If we try to do a headstand to match the image in the mirror then it actually "mirrors" it top/down instead of left/right.

Another example: looking at writing in the mirror, we've actually turned it around to point at the mirror. If we flip it over to point it at the mirror instead then again it'll appear upside down in the mirror instead of left/right flipped.

Edit: I should have read the article, because indeed this is exactly what it explains.

> Right, the mirror doesn't actually flip.

Isn't the point that it does? It flips front and back.

yes this is a great way to think about it

It's likely that a lot of those commenters only read the title, and not even the beginning of the article. I'm not accusing anyone in particular†, I just think it's worth acknowledging in terms of understanding how HN functions.

† Except myself—I do it sometimes!

I think people here just have an aversion to (some* ) cutesy explanations of things that just confuse things.

The article itself concludes with: "The reality is that the mirror isn't flipping things horizontally or vertically at all" and you wonder what mental model it thought it was explaining in the first place.

* We never tire of cutesy useless explanations of monads though.

Eh, what percentage of the commenters do you think actually read the article; what % watched the video? Some are just commenting from the title alone.

I'd guess that more than just some commenting didn't look at the article. There's complaints in the comments that only make sense if you ignore that there's an article at all.

But despite Physics Girl's video embedded in there being much better than the text, I can't fault anyone for not watching it. There are many situations where you can read through something, but can't watch a video.

I too generally prefer not to spend time on videos, although I was interested in this one so watched it.

However, nobody is requiring you to comment critically on something you haven't actually watched, heh.

> We never tire of cutesy useless explanations of monads though.

I haven't seen anything about monads for going on maybe five years now. It seems that trend has come and gone.

Most HN commenters are wrong. A mirror DOES flip one coordinate; the coordinate that is orthogonal to the plane of the mirror. That's what makes it a mirror, and not a window.

Tech people faced with a perception/biology/social issue in a nutshell. It matters that it feels weird, that's the whole point. "Flip" is a human word, it's not a mathematical definition.

> "Flip" is a human word, it's not a mathematical definition.

Why not both? https://en.wikipedia.org/wiki/Flip_(mathematics)

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