Challenge Questions

Turn your head sideways and you will find out!

It's a simple matter of ray tracing (from the eye to the object reflected off of the flat mirror) to see that the image remains erect. An inverted image must have the rays cross at some focal point, which a concave mirror would provide.

When you peer into a mirror the photons seem to converge from the image to the retina of the eye. Each photon strikes the mirror and is reflected at the same angle of incidence to the eye. That's the crux of the whole thing. The angle of incidence is exactly equal to the angle of reflection.

Tracing the rays backwards creates a divergent path from the eye in both the vertical and horizontal direction.

Look at graphically...

Nothing gets inverted, but the light is just reflected back to the eye (the blue orb). The next picture shows that the angle of incidence equals the exit angle for every photon. Photons never cross (and invert the image), just converge on the orb.

So, what you see is what you get regardless of whetehr it is vertical or horizontal.

The optics of reflection cause the image to be inverted. It's a z axis transformation, so doesn't affect up/down.

There's a complicated bit of processing going on in the brain, to make us see images that are 'true' and not reversed as in a mirror. I know when I started to write as a wee child, it was all in mirror images. Why it seemed right or readable to me I don't recall and can't imagine. I don't remember how they taught me not to do this. But it's a fact, I can't read (or write) mirror writing and lost the ability to do so when I learned to write rightly. Perception is a strange thing.

One of my daughters has the same capability. She learned to write in the mirror-image fashion at the same time she was learning to write normally. For what it is worth she is also very acute in solving writing and graphics problems. Seems to me her mind very quickly transforms optical images into different concepts.

you're wrong when you say " what a mirror does is flip the image in to out"

look at your own illustration and you'll see that it doesn't hold up; if it did the "m" in amoeba would have changed sides

Look for yourself, and apologise

We must keep in mind that the sensor of seeing image is actually the eye which is top

on the body .

According to Laws of Reflections the rays from right-side will be reflected back to left-side so mirror image (right to left) is obtained .Now why inverted image is not obtained in a similar way .I think the rays coming from bottom when reflected back to the eyes remained bottom-rays with respect to the eyes as compared to the rays reflected back from top-side i.e. top-rays .So no inverted image is sensed .

Ashraf

I think there is is some fundamental distinction between our concepts of up/down and left/right. May have to get some philosophers into this! We probably perceive up/down in relation to local gravity. Left/right seems to be more self-centred. Front/rear is arbitrarily defined for any object. NSEW has some meaning only on the earth's surface (away from the poles), while up/down has no meaning in outer space without further definition of the reference frame. (Why are we uncomfortable wiith maps which do not have north on "top"?)

So what do we mean by a reversed image? Looks like something to do with human perception and semantics! =TeeSquare=

The position of the eyes, is the reason for left and right and not up and down, and the minds perception of what information it receives the possible cause of left/right?

Regards JD.

You will see the same thing even if the eyes are placed on a vertical line on face instead of horizontal line.

Déja vu ?

The directions left or right are relative to the viewer. If in standing in front of a mirror one moves his right hand the right hand in the mirror would move as viewed. There is no reversed image. If one looks at the image as it would another person its a matter of prospective.

Deja Vu indeed. And it was simple the first time - but CR4 gives it a month. Sanity check, anyone?

The "challenge" as written only (sort-of) applies to a mirror whose surface includes a vertical. It's what the mirror actually does if it is placed to one side of you, as a mirror always inverts along the axis perpendicular to the mirror.

But it's not actually the case if you are facing the mirror - that inversion is not left-right, but front-to-back. You interpret it as a combination of left-right inversion and a rotation about a vertical; that is simply a function of how the eye-brain system has developed and how you have learned to interpret the world. But it would be equally valid to interpret the effect as a vertical inversion followed by a rotation about a horizontal.

A plane mirror with its surface horizontal would of course produce an image that was vertically inverted; unlike the front-to-back inversion, your brain would interpret this correctly.

The image is not inverted in a mirror. That is why top remains top and bottom remains bottom.
It is our perception mistake. On a person facing us the left and right are diagonally opposite. So we expect same from the mirror. But mirror shows the true image.

"But mirror shows the true image."

As an artist I have reflected on this occasionally. Because of our perception when looking in a mirror I have a theory as to why most people don't like the way photos of themselves look, but others may seem to think the photo looks fine. That is because that is how they normally see you, but the way we normally view ourselves is in a mirror.

Faces are not symmetrical, that is why when you cut a photo in half in Photoshop, copy and mirror each half, and fit each mirrored side together and compare, it looks like two different people.

I part my hair to the right side, but in photos it always looks to me that my part is on the "wrong" side and not as pleasing as a mirror image.

The same reason that a dog doesn't look like a tree when it barks. Misplaced semantics.

Great answer! The mirror image is not reversed from right to left, nor from top to bottom. If you raise your right hand, in the mirror image, the hand on the right side will be raised. Only if you are psychotic, and think of the image you see as another person facing you would it appear that it is "his" left hand that is raised. But I hope that most of us are not psychotic, and realize that when one looks in a mirror the image seen is not "someone else".

Holding a page of text in front of you when facing the mirror also proves that there is no reversal. Obviously, what would be the left side of the page if you were reading it conventionally is on the right when you hold it reversed, facing away from you and toward the mirror. This makes it a little hard to read. If the mirror were capable of reversing the image from right to left, then you could more easily read the text.

Perhaps for those who believe that the image is reversed, a good reality reorientation would be to reach out and touch the mirror. Right hand meets right hand on the right side of the mirror.

Hello Blink,

and realize that when one looks in a mirror the image seen is not "someone else".

Ermmm, I always have the bloke 'next door' watching me through the wall, as I comb my hair!

Take care.

If your eyes were placed one above the other on your head your image would be inverted. Your brain would probably reject that and process it more comfortably.

Jon

If your eyes were placed one above the other on your head your image would be inverted

The image still will not be upside down. You can make your eyes one above other just by tilting the head and varify.

Gsushas,

Like I said, the brain would take care of it.

If you went around with your head tilted 90 degrees the brian would most likely compensate in favor of convention.

Jon

Actually, it's not instinctive (or innate). The assignment of left and right relative to the body of another person is part of the learning process. It requires all of the concepts of "other", ones "left-right" perception, and practice at rotation. Try asking a young child who has only recently learned the terminology which hand someone facing it is using and you will soon see what I mean. Competence is not even that universal among adults. For example, speed and accuracy of left-hand right-hand identification were at one time important in the selection of military and airline pilots - I have no knowledge whether that is still true.

Hello Physicist?,

With reference to your post 46 (I believe it is) you make some very simple observations and write a very sensible post Sir.

I didn't mean to imply that this was 'instinctive (or innate). That's why I mentioned that we learn this through experience. My point is that this ability to learn by watching is so important to our survival (maybe because we are physically a fairly puny species) that we are born with a physiological system (mirror cells) to facilitate this type of learning.

While there does seem to be a lot of literature on this subject, it should probably be classified somewhere between a hypothesis and a theory. I tend to be pretty skeptical about psychological 'research', but I do have a weak spot for theories with a basis in physiology and biology.

Point taken - I suppose I just balked at the thought that knowledge of how another being assigned left and right had been relevant to the survival of any species.

You are right to be skeptical - I have probably overstated the case. The few articles I have read on the subject don't seem to deal with the left/right issue. I'm one of those non-pilot types who has some difficulty in knowing left from right. The upside of this problem as I discovered years ago when I was doing photolithography for a printing operation, is that I can read upside down and backwards.

For bilaterally symetrical beings such as us, the difference between 'this hand' and 'that hand' is very real, but the terms left and right are obviously arbritrary. It was while thinking about this aspect of the mirror question that I leapt to the conclusion that the mirror cell system might might be involved. If this idea is correct, then there would almost certainly be some sort of 'homunculus' like correspondence between the neural systems that control the right arm, and the mirror cells that simulate it.

Hello Physisits?,

"speed and accuracy of left-hand right-hand identification were at one time important in the selection of military and airline pilots" The original problem came out of the invention of 'formation flying' where such instructions as 'turn left' got interesting when confusion on left existed in a % of previously 'free style' pilots. It's still an issue and now carefully assessed in early flying training. If they can't tell L from R and they'll never 'solo'. Degree of certainty and delay in decisions is reassessed and still highly critical in aspirants to any commercial or military flying.

But interestingly those in air traffic control have to be highly skilled at 'relative left and right' of any vector. Similarly, in film all L&R is camera L&R, or a mirrored situation for those in front of camera. In theatre, stage left is house right (audience right) and either term is expected to produce the required response. More mundane is the ability of a driver to back a vehicle by its mirrors. Add a trailer, and competence drops dramatically. Add two trailers and very few can handle the computations.

Or in support of your point; it is learned and must be embedded to the degree that it is 'transferable' relative to an external entity. In addition to your point; very few 'learn' to re-reverse or apply it relative to a not directly opposite external point of view, (without confusion or delay), such as air traffic, film, theatre, and others above, or reading a map upside down, or indeed, navigating for a driver heading south via a map held 'instinctively' north up.

But it seems to me those who have had no need of relative external perception skills, so have had no need to learn further, might like to look at how a program, such as Solid Works or Pro E, produces a 'mirrored' part/body/section.

Thank you for the comprehensive update.

Just change left/right zto up/down so that left is up, right is down, up is right and down is left gives the solution of this problem, this is the relativity of the mirror or the coordinates.

But you are omitting the crucial effect: for a mirror that is oriented as you say, (and using your terminology) front is back.

You are staying front to front to a person looks like you and moves like you (this persoin is just a virtuell person in the mirror) - front to front like any other persons face to face.

The front of one person is the back of the other preson - like in reality!

Its still only a reflection of photons!

So my mirror cells are broken and I became left handed?

Handist?

When I look myself in a mirror the image is an "one-to-one" representation of myself. Relative to me (the real person) my left hand appears to be on my left side, my right hand on my right side, my feet on my down side and my hair on my up side. There is a symmetry which is irrelevant of the x and y axis. Beyond this everything is a matter of definition. This means that -relative to my image- my right hand appears to be his "left hand". If my image was a real person he would consider it this way. But, relative to me, everything is normal and symmetrical.

When I look myself in a mirror the image is an "one-to-one" representation of myself. Relative to me (the real person) my left hand appears to be on my left side, my right hand on my right side, my feet on my down side and my hair on my up side

Yes, except hair. Many of us may not have!

When we look in a mirror the image is an "one-to-one" representation of ourselves. Our left hand appears to be on our left side, right hand on our right side, our feet on our down side and my hair (or bald top) on our up side. But when we start imagining ourslves in that body in the mirror, then the confusion starts. Then our left hand becomes right hand in the vertual image. Our right hand becomes lefthand of the image. But bottom and top remain as it is to prove that we are confused.

The principal is the mirror's image is point for point reversal of arriving photons. It's action is analogous to a transparent plane, or the film plane of a camera. But because the light is 'reflected' the image 'returned' is an optical facsimile of that viewed on the back of that plane, or image on film. E.g. look through the wrong side of a 'transparency' or 'slide' you see the 'mirror image' of the picture. No "mirror axis", no "mirror orientation" are at play and it's exactly the same for one or any arrangement of eyes and or brains.

If this is still not clear, have a look at how a virtual image is made in "front projection" a cinematographic technique - pre CGI and 'blue screen".

It's not reversed either up/down nor left/right. It's reversed front/back.

Indeed. As if the image passed through the mirror as was seen from behind.

Not knowing the scientific explanation, common sense tells us that what we see in a mirror is what another person sees when he or she views us

What one thinks is a reversal of left and right is no reversal at all, it's just one's conception of left and right that has changed.

As for a reversal of up and down, that doesn't happen because it hasn't changed from your perspective.

Other than that, I do not know any scientific formula or law that would describe the phenomona.

Ken Leigh

If you stand in front of a mirror holding a piece of cell or thin paper with printing on it (that said printing may be visible through back) but holding it with the writing toward you, the writing on the back is now the correct way around in the mirror.

Is the image any different from another person's point of view, or a photo taken from the mirrors point of view? For you and your page – no, left and right are 'camera relative' - but the writing on the store window behind you is "reversed" in the mirror but not the in photo. As said, the image is a point for point virtual equivalent of that that passed through the mirror.

The easiest way to demonstrate that a single reflection is not the same as changing your angle of view is to look at a helix in a mirror. The mirror reverses the direction of the helix (chirality).

The mirror reverses the direction of the helix (chirality).

Your response illustrates why I gave Palinurus's response (post #13) a good answer vote.

The helix, as seen "in" the mirror is not reversed in several senses. The first and most obvious is the proximity to a mirror has no influence at all on the actual 3D construction of the helix.

The second sense in which it is not reversed is precisely the same sense that allows one to say that our perception of an image in a mirror (of course the image is not "in" the mirror in any real sense) is not reversed from right to left. The right side of the helix remains on the right, and the top of the helix remains on the top.

A third (only slightly different) sense in which the "image" is not reversed is this: Assume you hold a helical fluorescent bulb in your hand while standing in front of a mirror. (Perhaps those who argue that the mirror reverses front to back would then argue that when we stand in "front" of a mirror, we are really standing behind the mirror.) The side of the helix that is away from you (the one facing the mirror) goes from right to left as it goes upward. The image in the mirror is exactly the same: that side of the lamp is seen to go from right to left as it goes up. Clearly, no reversal takes place.

It seems the only sense in which a reversal takes place is that some people might perceive the image to have reversed. A person of this type might say that the image of text on a piece of paper that he has reversed to face the mirror also "appears" to be reversed, but of course is not. (Assuming he is holding the paper in his right hand and near an edge of the paper, then the text nearest his right hand is also nearest his right hand in the mirror "image".) (If such a person had flipped the paper around its horizontal access, he would claim that the mirror had turned it upside down.) Mirrors do not have the ability (as far as I know) to alter the reflection dynamics outlined by Anonymous hero in post #9.

(Assuming a stationary eye, etc, etc, etc.): Mirrors also do not have the ability to represent, in a realistic way, a third dimension (in and out) any more than a computer screen does. A wire frame drawing on a computer screen is therefore inherently ambiguous. Rendering and shading the surface does not "make" the image 3D, it simply helps us perceive that the drawing was intended to represent something which has three dimensions. Thus, there are those people who claim that a mirror reverses "in and out" or "away and toward", while any such reversal is purely perceptual. At least in my strange perceptual world, when I move my hand closer to a mirror, it appears to get closer to the mirror.

"Your response illustrates why I gave Palinurus's response (post #13) a good answer vote." Hmm, shades of ad hominem. But no sign that we have substantive communication.

So please bear with me,and go with the following one step at a time.

If you consider the image as 2D, looking straight-on the mirror, left is left and right is right. But the image is not a 2D image, it is 3-dimensional.
In order to communicate, I shall ask you to consider a mirror whose surface faces south. East-west and up-down appear unchanged in the reflection - but objects (and parts of objects) that were south appear north in the reflected image, and vice versa. That is the reversal that really does occur in the mirror image.

Returning to the helix: try looking at a very large standard-type screw. Place it so that the tip is facing you. Without touching the screw, optically and mentally trace the direction of rotation of the thread as it goes away from you. For a standard screw this should be clockwise. Now place the screw with its tip facing the mirror. Again, trace the direction of the helix as you go away from yourself along the screw. This will now be anticlockwise. This is what I understand by chiral reversal.

Am I making sense yet?

if i stay in fornt to the plane mirror and looking into my face - may i make a distinction i'm the picture in the mirror or i'm myself?

Ad hominem? Only in its more literal sense "to the man" rather than "against the man". I always value your posts, and have said in several places around CR4 that virtually all of your posts are "Good Answers". The reason I responded to your post here is because it is well-thought-out.

My praise of Palinurus's post has to do with the complexity of the language used re the subject matter, and our own differing use of the language, which depends strongly on our experiences and background. Visual perception was a strong interest of mine in college, and I still find myself "seeing" things very literally, if I want to. Hence, I see no right-left reversal in the mirror, and only see that "reversal" (a different word that reversion, which comes from revert, not reverse) if I imagine myself to be looking at someone other than myself.

I can tell, (consciously) from eye muscle feedback, if I am looking at something further away or closer. So when I trace a helix mentally (whether it is held vertically or horizontally, facing the mirror as you suggest) I see no reversal in that plane either. When I move back away from the mirror, it looks to be like I have moved back away from the mirror. I am aware that when I focus on something on the mirror surface (e.g. a fingerprint), I am focusing at half the distance I perceive when focusing on that person "in" the mirror -- the image for which is neither in nor on the mirror. The only real image is on my retina, and that image is strictly 2D (ignoring the fact that the retina itself is actually spherical).

To perceive a third dimension when looking in the mirror (to understand what we see in the mirror is not a photograph of us we have to move, to change the 2D image on out retina or to refocus on something closer or further, to engage focal distance perception via eye muscle feedback, etc) Then, through perceiving occlusion, and focal distance, we can interpret the object we are seeing as 3D by comparing (subconciously for most people) one 2D image with another. Any 3D image exists only in our "imagination." Our retinas have no sensors for depth, with depth perception being processed from a 2 dimensional retinal image (again, ignoring the fact that the retina is rather spherical) by our brains.

The challenge question is very simple, and has a simple answer: the premise is wrong; there is no right-left reversal. The very fact that you can read "ambulance" in your rear view mirror (something which, for me, delays recognition a little -- I'd rather have it read the right way around, just like the letters on the front of many commercial trucks) proves that there is no reversal. If one believes that there is a reversal or inversion in the third dimension, that still does not "cause" a reversal from right to left... because the reversal from right to left does not exist.

I have to go, and will come back, but have been very short on time recently, so don't take a slow response as a sign of disinterest in your insights, which I always find interesting, no matter how ludicrous they may seem to rational people. (I'm kidding of course -- as I said, I think all your answers are good answers.) What you say makes perfectly good sense, given a particular linguistic interpretation.

"The very fact that you can read "ambulance" in your rear view mirror (something which, for me, delays recognition a little -- I'd rather have it read the right way around, just like the letters on the front of many commercial trucks) proves that there is no reversal"

I'm completely mystified by this. In one clause you say "rather have it the right way around", in another "proves that there is no reversal". The fact that you have any additional difficulty proves that there has been a significant change of some sort. The fact that you can still do it reasonably readily merely shows that the eye-brain system is quite good at this particular transformation.
On the other hand, the fact is that there is no left-right reversal of this image. But, being in front of you instead of behind, the image is exactly the same as it would be if you turned the world around a vertical axis by 180^O (which reverses left-right as well as front-back) and then reverse left-to-right (to bring left-right back to their original positions).
(You would get the same subjective effect if the writing was on a transparent screen, and you looked at it from the back of a transparent screen - the difference is that in this case you move yourself physically).

The mirror does not reverse left and right. Left and right, and up and down for that matter are perceptions dependent on the perspective of the veiwer.

True and true but "are perceptions dependent on the perspective of the viewer." no - it's straight forward virtual optics, a camera will see the same image. Has no brain has no 'perception' conditioning.

The Answer is relatively simple: It's a matter of Relativity. The object is either left or right relaqtive to the viewer, and either up or down relative to the environment. The mirror reverses the point of view, not the environment.

its just as if u are seeing the paper from the rear of it!!!!!!!!

your left hand is a mirror image of your right hand, if you had a left-hand latex glove and wanted to make it fit your right hand you would have to turn it inside out. The mirror gives you the geometrical equivalent inside-out view of yourself. There is no doubt a transformation matrix which describes this but I don't know it off the top of my head.

http://brain.oxfordjournals.org/cgi/content/full/131/12/3443

Since the image is virtual and behind the mirror (schoolboy physics lessons), maybe it only exists in the head of the viewer

When using the left hand motor rule field, current, motion visual mnemonic

http://en.wikipedia.org/wiki/Fleming's_left_hand_rule

you can convert from conventional current to electron flow by either using your right hand or using a mirror - but while the M carefully written on your thuMb would be fine, the C on your seCond finger and F on your First finger would be reversed.

and of course the reverse is true for generators.

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

does the polarization change on reflection?

many mirrors polarize, not all!

There is no reversal. It is an exact contact print.If one keeps going forward till contact with the mirror, this can be seen. We are looking at the print from the back as it were, which leads to a 180 degree turn around. There is no turn around in the vertical plane, so top is still top. Bioramani

As a sequence of my post #19...

As I said the whole issue is a matter of definition. For all of us the "upside" and the "downside" (i.e. the y axis) are common, as we all are stuck to the ground and stand on our feet (because of the gravity). The "upside" and "downside" is in the same direction for all of us and it's irrelevant of facing to each other or not.

Unfortunately, it's not the same concerning the directions on the x axis. We use to "separate" the world around us in another way (very convenient for our daily actions): The part of the world which is -generaly- extended on the one side (relative to us) is called "right side" and the other part which is -generaly- extended on the other side is called "left side". These "right" and "left" sides are not common for all of us (as general directions) because each of us can stand in different positions (i.e. facing different directions). So, for two persons facing to each other, their "right" and "left" sides are in opposite directions. For two persons facing in the same direction, their "right" and "left" sides are in the same direction.

That's why I said that this is a matter of definition. I raise my right hand in front of a mirror. Me and "my image", we both raise the hand in the same "general direction". But (because we are facing each other) I call this direction "right" but "my image" calls this direction (unavoidably) "left".

Let's say that there is a camera behind me recording my back side. And I see this image on a TV screen in front of me. I raise again my right hand. Again, me and "my image", we both raise the hand in the same "general direction". But, in this case, (because we are facing in the same direction) I call this direction "right" and "my image" calls this direction (unavoidably) "right" too.

we use same words but talk about different things!

Simply a matter of perception. If your friend stands in front of you facing you, and raises his left hand when you raise your right, you will see the "same side" effect without any mirror present. If he faces away from you and raises his right hand when you raise your right, you will see the hand raised on the "same side" of the body as before. Did you ever notice that when shaking hands the two of you "cross" hands?

The explanation is simple: Light travels in straight line.

There really is no complexity or confusion!

The brain tells us exactly what the eye sees and the eye sees exactly what is to be seen. The "trick" is to realise that the eye/brain sees light and the light that is seen is exactly as if the "image" of what is behind the viewer were painted onto a glass sheet and the glass sheet was then moved from behind the viewer to in front of the viewer - at which point the viewer is then looking at the back side of the image on the glass.

The so called inversion comes about by comparing what the viewer now sees to what he/she sees AFTER they have turned around 180 degrees to compare with what is behind. If the whole routine were completed with the viewer laying on his/her side then he/she could equally say that there was an "up" "down" world view inversion.

На самом деле зеркало не меняет соотношений левое\правое или низ\верх, а только вперед\назад.

I think the translation from Russian is "In fact, the mirror does not change the relations left \ right or bottom \ top, but only forward \ back."

Thanks, Jim

Hi jim, looks like you just about got it right my friend, thank you.

"In fact, the mirror does not change the relations left \ right or bottom \ top, but only forward \ back"

Take care

Jim,

Better translation?

As a matter of fact the mirror doesn't change ratio or proportions from the left to right or bottom to top, just back and forth.

Jon

Ok, it turns out that my assumption that Wiki would cover it was 'optimistic'. Nor are any of the reference links of adequate clarity regarding the image 'creation'.

So, this Introvision schematic is our start point. Note if you trace one edge of the projector beam to the mirror, then to the 'stage/screen', it 'changes sides' or the image on the 'stage/screen' is laterally reversed This is analogous to you looking in a mirror and seeing a 'left to right inversion', which as said earlier is simply a point by point image replication, working on exactly the same principles as tracing an edge has illustrated.

The S-screen is highly 'reflective' (in the manner of road signs), so the image is visible to the camera. Trace that same edge from projector, to the mirror, to S-screen and back through the mirror, to the camera lens –. E.G. light on 'projector right' (upper side in the dia.) arrives back at 'camera left'.

Now we get to the 'interesting part'. Wiki basically gets to; if you shone the projector directly at the actor/stage/screen, the image would be visible on the actor. To wash this out the actor would have to be highly lit, producing 'spill' problems on the screen. So only '50%' is sent to S-screen.

If this was the end of it then the 'background' would still be 'dull'. This brings us to the 'projector screen' function. This screen is square to the projector (the image is not 'reversed') and reflects (in the sign manner) an image visible (to the camera) in the back of the semi-silvered mirror, (which reverses it). Thereby the camera sees 50% of exposure in each image. Alignment and distances are obviously critical to both 'same size' and 'exact overlay'.

However the 'on topic' part of this is the camera is seeing one image directly on S-screen and an identical but virtual image on the back of the mirror. Each has been separately 'reversed' so both are 'mirror'. The 'cure' for this is to 'flip' the film in the projector so projection is 'mirror', (in practice you make a mirrored print).

I hope this makes clear how 'point by point image replication' works. If not then square the mirror up to the projector. Your edge of cone traces will come back left at left, right at right, top at top, bottom at bottom. When you look at this image on the screen, now behind the projector, you will call it 'mirror' and say it's "reversed" in one aspect only. If you look at the image from the back of the screen (presuming some transparency) it's not reversed in any aspect.

The answert is quite simple. Unlike a lens, which refracts light and which does flip the image both right/left and up/down, the mirror is displaying to you your reflection. When you stand in front of the mirror, your right arm is on the right of your body (probably why it is called the right arm). The mirror displays it on the right also. The light from you hits the mirror and comes directly back. Your right arm is still on the right in the mirror image. In reality it does not "flip" right to left, it just displays a direct reflection of you. This is why you are also still rightside up. One can say the image is flipped only when comparing it to a real 3d person standing in front of you. Then their right arm is on your left (but still their right!). But they are still right side up!

As an example, take two balls, one in each hand. Throw them both straight at a wall. If you threw them perfectly straight, the ball from the right hand will come back to the right side. Likewise, the ball from the left will come back to the left side. This is what is happening to the light. It is a direct reflection.

If your Mac or PC lap/notebook has a camera built in, place it next to a mirror. Take turns looking at your face in one then the other. Rotate the mirror and rotate the computer. Is there a difference? Notice, the computer camera is not in the center of the screen. Ah, incidence! The brain, with practice, will iron out the reason empirically.

Surely this question is not referring to simple personal reference frame orientation?

There is no reversal of images/objects.

The simple reason why writing or left/right seems to be turned around is because the Cartesian reference frame of the viewer relative to that of the image in the mirror is rotated by 180° about the vertical axis (i.e. your image in the mirror "looks" back at you in the opposite direction than you are looking at yourself - so your x and y coordinate axis are rotated through 180°).

The image is not reversed left to right, just your preciption of reality is confused. Hold up a sign in front of you and read the sign in the mirror, the letters appear backwards, but you can still read them. Turn the sign 90 degrees and the letters still appear backwards. It is a trick played on your coordination of what you see directly and what you see reflected.

What we think of as left right inversion is primarily due to the way our brains process information about our bodies. Normally, visual and proprioceptor info about the right hand, for example, agree and we are able to make fine motor movements without difficulty. If we "flip" the visual input, as in a mirror, the brain initally has a conflict between the somatosensory and visual inputs and seems to send information to the wrong side visual cortex. Motor skills are then coarse and inaccurate. If you continue looking at the inverted image, after a week or three, your brain will sort it out and line things back up again.

We've also got an up/down sensor in the brain, and we use that for orientation as well. That's about as slow to respond as the left/right.

But, there is no front/back sensor, so we don't easily perceive any conflict. You can set up a TV camera and monitor so that you watch yourself facing the wrong way and, watching only the monitor, easily pick up small objects and accurately manipulate them.

If you do this with machine vision, it doesn't care which axis is screwed up. It just knows you've got a "handedness" reversal.

Very interesting and thought provoking but at a guess you are a gamer, not say a SCUBA diver or aerobatic pilot.

So consider this; How do you know what your face looks like? What confusion do you have cutting your own hair? Do women putting on makeup have these issues at all?

I'm none of your choices. Why those, and what does it matter?

I know what my face looks like from mirrors and photographs, and I recognize myself in both.

I have no confusion cutting my hair. I shave my head every day. The first two weeks, I had some difficulty; now I don't.

My religion forbids contact with women, so I have no idea what they do.

angle of refraction equals angle of reflection.

It cant flip top to bottom because the angle is 180 degrees out. it doesnt actually flip at all. it is the EXACT reflected image. the light bounces off of the object, hits the mirrior and returns to the object at the exact same angle. so an object to the right in the real world will be to the right in the mirror also. we simply see the light from the object as it is going away from us instead of toward us. There is no flip.

How can you write this when some in the thread have already addressed the reality? Assuming that flip has any meaning, the image is flipped in the direction perpendicular to the mirror surface.

The plane mirror dpon't reverses the picture -. the reversation is just the projection to the human Eye or Brain!

If I look in the mirror, my right Eye is still on the right Side, i don't change into (behind) the moirror, i stay still at the same place! And ny Right Ey/Arm/Leg (anything else) is still at the same place! If I move my roight hand than the picture in the mirror moves this hand too - it looks like moving the left hand in the mirror but it's still the right hand!

The mirror chnges nothing - only the people lookoing into the mirror think the mirror changes something! But it's all unchanged - just the reflected light to the human Eye lets us think that there is a change of the sides!

It does invert the image - the most convincing way to demonstrate this is to look at the reflection of a helix - this reversal of handedness is inescapable.

The inversion is always perpendicular to the plane of the mirror. If the mirror is to your left or right the inversion really is left-to-right. If it is above you, the inversion will be vertical.

If the mirror is in front of you, the inversion is front-to back. The reason that you interpret it as a left-right change is that your first step in matching the image to the original object is to imagine the original object turned 180^O to face back at you. Compared with this imagined object, the image is reversed left-to-right. The interpretation of left-right inversion remains consistent as you turn the object - or indeed yourself.