Just saw this on xkcd

When you look at words in a mirror, how come they’re reversed left to right but not top to bottom? What’s special about the horizontal axis?

I’ve figured it out… Sort of.

hmmmm

It’s obvious, but I damned if I can explain it!

Writing on acetate sorts this out if you have any confusion…

Write on a sheet of clear acetate, hold it up facing the mirror, stretch out your arms so you’re looking at the back of the acetate.

Who has acetate lying around?

Will a semi-opaque sandwich bag do?

No, but you can use a dark pen and a thin piece of paper. But I’m still not sure if it does explain it fully..

Remember, the mirror isn’t reflecting what you’re seeing here, it’s reflecting the other side – but it’s showing you what you’re seeing (if that makes sense).

I guess it’s to do with how we define directions. So up and down are always up and down, but left and right we define as relative to the individual. IIRC the’re some tribe somewhere which doesn’t have language constructs for left and right – everything is in absolute positioning. Which makes me wonder if things in a mirror look reversed to them too.

It’s not reversing it, you’re just looking at the other side.

So why don’t you see the back of your head in the mirror?

I guess it’s to do with how we define directions. So up and down are always up and down, but left and right we define as relative to the individual.

That’s sort of the explanation I came up with. Up and down/top and bottom are constant, right and left are relative to the direction you’re facing, and the mirror is facing in the other direction to you.

Still not sure if it explains it fully though.

So why don’t you see the back of your head in the mirror?

Cos it’s a reflection and you don’t have eyes in the back of your head. (Although my mum does, apparently)

Okay, so why does the sticker on the back window of my car look the right way around in my rear-view mirror? 😉

Simples. The text (when looking at it in the mirror) is correct. Letters on the right-hand-side of the paper are reflected at you from the right-hand side of the mirror. Top to top, bottom to bottom etc……

Interestingly, this is a psychological effect that’s been noticed with webcams – people think they look odd or wrong in a webcam because they’re so used to their mirror image, the webcam view (which isn’t reversed) looks weird.

don’t we actually see things upside down, due to the way light comes through the iris, and our brains adjust it for us? going to google.

How about if it’s a palindrome printed on the sticker on my car window?

When you look at words in a mirror, how come they’re reversed left to right but not top to bottom? What’s special about the horizontal axis?

They’ve not been reversed, they’ve been reflected.

A reflection will look reversed from top to bottom (but not left to righT) if it’s, for example, the reflection of a mountain range in the water of a calm lake.

http://en.wikipedia.org/wiki/Perceptual_adaptation

Just draw the path of the light from the object to the observer via the mirror, then track that back to where the image would appear to be to the eye.

@spchantler – yep the optics of the eye produce an upside down image on the retina that the brain rectifies. Studies with people wearing glasses the invert the light coming into their eyes have showed that brain can ‘unflip’ the image after a while too. Which is why Australians can still see properly.

Look forget the mirror question, what’s the answer to the blue/violet question?

Look forget the mirror question, what’s the answer to the blue/violet question?

I think the intensity of blue light is far greater than the violet light, and our eyes are also very poor at picking up violet.

But that’s massively outside my field of knowledge, so don’t quote me on it.

I think you are right, just found a similar explaination here

Rayleigh scattering is the phenomenon that explains the color of the sky, where light of shorter wavelengths gets scattered by the air by the inverse of the fourth power of the wavelength as given in the comic. In the visibile spectrum, blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. This leaves the impression of a blue sky.

The violet thing:

The answer given isn’t quite right there. It’s not shorter wavelengths that get scattered in general. Oxygen molecules are the right size to scatter blue light specifically. Smaller or larger won’t scatter off them as well. Hence blue.

also its only when we look at writing it appears reversed, because its always read from left to right, actually everything is reversed, try holding a mirror up and navigating you way around your house, backwards. stay off the stairs tho,

Is this not as simple as being down to the fact your eyes are on the horizontal axis?

Is this not as simple as being down to the fact your eyes are on the horizontal axis?

Close one eye. Have a look at something in a mirror.

Tilt your head 90 degrees. Have a look at something in a mirror.

The violet sky thing isn’t really due to the intestity of the light.

It’s down to how our eyes work. Simply…

Rods and cones, cones for seeing colour
3 types of cones optimised for different wavelenghts
But its possible to confuse them.
Violet light of a certain wavelenght creates the same message from the 3 sets of cones as blue light and white light.

Hence we percive the sky to be blue even though its wavelenght makes it purpley blue.

More sciency here:
http://www.msnbc.msn.com/id/8631798/ns/technology_and_science-science/t/why-skies-are-blue-instead-purple/

How about this.

Write a word on a piece of card. Pin it to the wall, and stand facing away from it.

The text is now in the same plane as it would appear to you if you were looking at it in a mirror, yes? Ie, it’s reversed relative to you.

Now, turn to look at it the right way around. Which way did you just turn your head? That’s what’s special about the horizontal axis; it’s how your brain interprets a mirror image.

(ObDisclaimer; I just made that up)

Oxygen molecules are the right size to scatter blue light specifically.

Nitrogen, shirley?

Mirrors don’t reverse up and down – and, in fact, they don’t reverse left and right either. They simply show us our reflection, and that appears to reverse the direction we’re pointing. The reason this also seems to reverse left and right is because these two directions are defined relative to our own direction.

Don’t believe it? Then stand opposite someone else and both lift your right arms: you’ll initially think that the other person has lifted the ‘wrong’ arm. They haven’t: it’s just that they’re pointing in the opposite direction to us – so their idea of left and right no longer agrees with yours. It’s the same when you’re looking in a mirror; your reflection created the illusion of reversing your direction.

Or get a mirror, put it on the floor, stand on it.

Voila, you have a mirror the “reverses” up and down but not left and right.

Blimey what an overthought degree of elimentary stupidity!

Next you lot will discover you’ve got opposable thumbs and how to start a fire!!!

😉 😀

What I want to know is that if Australia is the other side of this spherical planet to us, why the Aussies don’t fall off?

killwillforchips – Member
Blimey what an overthought degree of elimentary stupidity!

Oh dear…

thepurist – Member
Which is why Australians can still see properly.

😆 😆

What jfletch said.

To be more specific, mirrors don’t reverse left-to-right… they reverse back-to-front.

So why can’t I see the back of my head?

</Deliberately Obtuse>

So why can’t I see the back of my head?

</Deliberately Obtuse>

Because the back of your head is behind you, so in the mirror it’s in front of your face, which is in the way.

So if I wrote bop on the back of my head and looked in the mirror, would it read bop or pob?

So if I wrote bop on the back of my head and looked in the mirror, would it read bop or pob?

From which direction?