Why does a mirror switch right and left?

Vasek, if you were as ugly as a 3-eyed blob with 3 arms and 3 legs looking at the mirror, you wouldn’t even be wondering about why a mirror would switch right and left. You’d only notice that you’re looking at a right-handed version of yourself (if you considered yourself left handed, that is). We get so confused about the magic properties of the mirror because we have a keen sense of up and down, and right and left—in other words, we’re spatial chauvanists, thinking that there’s a top and bottom to everything, with a right and a left side. For a 3-eyed blob with 3 arms and 3 legs sticking out in all directions, that has no meaning.

I think Mistress Bekki has said the magic word here, “chirality”.

Edit: Vasek, your chauvanist sense of up, down, right, left is so strong that you still can’t help but sense a problem with labels. You feel that a mirror reverses a label between right and left, but let’s suppose that the label is printed circularly, so that you cannot unambiguously speak of left and right. Then what? To you, an ordinary label has a “right and left”, but what do you say about a label that is upright, i.e. the “left” is “down”, and “right” is “up”. Then what the mirror is doing, using YOUR notions, is reversing top and bottom. Yet, you don’t see that when you are laying down on the ground (in order to read the label!), you still insist that it is reversing your left and right.

Let’s say the ugly blob in outer space has snapped a photo of his reflection in the mirror. He compares it with a photo taken of him directly. He will notice that, no matter how he rotates the photos relative to each other, he cannot get a match. Neither can you, even though the difference is more subtle. Now, try asking the blob where is the “axis of reversal”. He will say, “it is arbitrary, I can make the photos match by reversing either one by any axis that I choose”. But you are going to choose just one, the one corresponding your own axis of symmetry, even though any axis of reversal will work.

Edit 2: I will try again in a different way. If you saw yourself in a mirror with left and right reversed, it wouldn’t perturb you. If instead you saw yourself in a mirror with top and bottom reversed, it would bother you a lot. Yet, both are true. You ARE in fact top and bottom reversed in the mirror, it just doesn’t look like that to you. But if I were laying on the ground while you are standing up, I would say that it’s your top and bottom that’s reversed, even as I say that it’s my left and right that’s reversed.

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Vasek, you can bend backward before an vertical mirror with your lettered Tshirt (or put a book in front of it) and still the text will be flipped horizontally.

Have you considered why in a concave (spherical )mirror (such as a spoon) up is down, right is left and left is right.

Edit: Dear Vasec, Trak’s answer inspired me and has made me laugh, “so much for conservation or vertical axis”.

But I am sure that Scythian meant well by pointing that you should try to forget all preconcieved knowledge of “labeled directions” and think out of the box. Although the manner in which he has expressed it might sound a little harsh.

Use your imagination, make your mirror slowly become concave, and flat again, and concave again….. take it in outer space if you want to, there are no limits in imaginary land!

Imagine that you are one single asymetrical letter in space looking at the mirror, rotate the mirror about its center in an x,y and z axis while the mirror is still in a never ending “circular mutation transition” from flat to spherical to flat…

Oops, I meant rotate yourself (as an asymetrical letter) in front of the ever changing mirror. Imagine that you can see the mirror image from every angle in which you rotate.

Good luck!

Have fun=)

Sleep well

xx

It doesnt. Instead it changes foward/backward directions. Changing of left and right is just a popular myth. Mirrors don’t switch left/right orup/down, but we do especially when we rotate objects about an axis so as to orient them facing a mirror. Take a piece of paper and write a word on it. To get a mirror reflection of that word, you can flip it about the x-axis or the y-axis. The default choice is almost universally y-axis, which is why the text appears “mirror-reversed” or right-to-left. But you could as well flip the piece of paper about the x-axis, in which case the text will appear upside down, but left-to-right.

A mirror transform (x->x, y->y, z->-z) flips the CHIRALITY of any object. A right-handed screw in a mirror appears to be a left-handed screw. How does this happen?

The first thing to note in that transform is that x (horizontal in the plane of the mirror) and y(vertical) are not the “special” axes. It’s the z direction (perpendicular to the mirror) that is special and gets flipped.

Anyway, as you face forward, right is clockwise 90 degrees from up. In other words right is the cross product of forward and up.

When z->-z, that flips the definition of forward. Up is still up. So the cross product of forward and up flips, which means that right becomes left and vice-versa. Clockwise becomes counterclockwise. A right-handed coordinate system (ixj=k) becomes left-handed (ixj = -k).

This reminds me of an interesting problem in physics/math. How would you describe right-handed (or clockwise) to an alien? There’s no way you can do it without either sending him a physical example or referring him to a physical phenomena (like the weak interaction) that is not invariant under a mirror transform.

–Vasek. Ah, I see your point. You are asking why up is still up under y->y, but right is not still right under x->x. My answer is that it is purely convention. And that convention stems from the fact that we have bilateral symmetry in our bodies. The mirror image of me clearly has a head which must be up. Then right can be defined relative to up and forward as I mentioned above. So Dr. Octavian’s answer isn’t completely nonsense. It’s not just the placement of our eyes that causes us to say that “up is up”, but the bilateral symmetry of everything about us. Suppose I had a big claw on my right hand and I called that side clawside and the other side noclawside. That claw is what immediately draws my eye and gives me my orientation. I would probably say in that case that clawside/noclawside are untouched by the mirror but that up and down ARE flipped. This is essentially what happense if you turn yourself horizontal.

One other thing to note: if you have kids, you know that they learn the difference between up and down (and front and back) very early. They don’t learn right and left until they start school or start writing and noticing an assymetry in their bodies that lets them remember which is right and which is left. So up and down are much more fundamental to our perception and orientation than right and left.

Once you come to grips with this, try:

http://answers.yahoo.com/question/index;_ylt=Ap2Kv…

*** Why does the text in the mirror image

*** look flipped along the vertical axis?

It does not.

The text is mirrored, not flipped AROUND any axis.

The concept of left right refers not to the sides (at least not in this context) but to chirality. On the other hand the concept of up and down refers to the direction, the direction of axis. Since the mirror is “vertical” (you said “vertical” how do you define “vertical” anyway) the axis down->up is not affected by the mirror, because this axis lies in the plane of the “vertical” mirror (here we go, the definition of “vertical” mirror: a mirior in which down->up axis lies).

Place a flat mirror on the floor “horizontally” and observe your image head down feet up. So much for “vertical” axis conservation.

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Let me take a different view. If I arrange lasers as shown in the following image

http://i233.photobucket.com/albums/ee201/vcpandya/…

and the I hold a paper in front of that, I get the following pattern on that paper

http://i233.photobucket.com/albums/ee201/vcpandya/…

Here Paper is a mirror and as you can see the same thing happens with the mirror and we get things flipped horizontally 🙂

If I were to use this concept practically, I will think of a printing press where letters on a master print is transferred on a drum (mirrored) and then when that drum rolls on a normal paper, it again transfers (mirrors) that text on normal paper to give us correct print.

Now if we see our reflection in water it gives us example of vertical flip.

I hope I explained it correctly with whatever physics knowledge I possess 🙂

This was one of Richard Feynman’s favorite brainteasers. http://varatek.com/scott/feynman_problems.html#mir…

To add to the answer’s above (I like Bekki’s followed by Track’s), a mirror works in all dimensions (2, 3, 4, 5 …), and if you are lying on your side, up remains up in the mirror. (Oops, you asked this while I was looking up Feynman).

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Looking at a mirror is like being on the opposite side of the mirror and facing the same way your are now and looking backwards through the back of your head. Left is now viewed as right (and rightly so), but nothing else changes.

Here is another example of a mirror image if you could travel faster than the speed of light. (It is an answer to a Track P question) .. http://answers.yahoo.com/question/index;_ylt=Ai84f…

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I posted another follow up question: http://answers.yahoo.com/question/index?qid=2904…

The light leaving your face reflects off the mirror and comes directly back to you. The mirror does nothing to the light rays other than reflect them back. So if a ray of light leaves your “right side” it simply “appears” to originate from the “left side” of your image in the mirror. Light only travels (in your bathroom anyway) in straight lines.

Isn’t it because your eyes are placed on either side of your head, so the disparity you see is horizontal. I think if you had en eye on your forehead and one on your chin instead, you’d see things flipped vertically. Very good question though; I remember scratching my head over that one 🙂 (still not sure if I’m right!)

ADDED: Scratch that, that’s nonsense…

This is hard.

ADDED AGAIN: in light of Scythian’s second edit; that finally makes sense, and I wasn’t a million miles off… if you had en eye on your forehead and one on your chin instead, you would indeed see things flipped ‘vertically’, if you were used to perceiving the world tat way 😀 It is our preconceived notions of left and right that are at fault! It really felt like a lightbulb going on when I got this, thanks Scythian 🙂 and cheers to Vašek for the question; a really good one!

It’s actually explained in some introductory college physics textbooks. I don’t remember and don’t have my textbook with me (which is great at explaining stuff in a very practical and understandable way), but let me find the name so maybe you can check it out of the library.

(will edit once I find it).

I just faintly remember that it has something to do with the way the mirror absorbs/reflects/refracts (one of those, maybe) light.

Source(s): Edit: http://www.conceptualphysics.com/books.shtml