carlc@tektronix.UUCP (Carl Clawson) (05/28/85)
This has more to do with clear thinking than with physics, but here goes: When you look in a mirror, the image you see is reversed left to right. Why is it not also reversed in the vertical direction? -- Carl
throopw@rtp47.UUCP (Wayne Throop) (05/30/85)
> This has more to do with clear thinking than with physics, but here goes: > > When you look in a mirror, the image you see is reversed left to right. > Why is it not also reversed in the vertical direction? > > -- Carl Well, actually, it isn't a paradox, and you don't need to think very clearly either. The usual phrase to ask the question is "Why do mirrors reverse right-left, but not up-down?", which in fact is the name of a short story somewhere if I'm not mistaken. However, the usual answer to this problem (pointing out that flipping the image in the verticle axis rather than the horizontal axis is a convention due to gravity bias) I find unconvincing. So here is a more convincing (to me) explaination. Imagine yourself facing north just in front of a south-facing mirror. Point east. You image points east. Point west. Your image points west. Point up. Your image points up. Point down. Your image points down. Point north. Your image, tricky fellow, points *south*. And when you point south, your image points north. Therefore, it seems simple to conclude that mirrors reverse front-back, not left-right, nor up-down. Note that by a front-back image reversal, mirrors reverse *handedness*, which is conventionally associated with left-right. This, coupled with the above mentioned gravity bias (things are normally assumed to be symetrical around vertical axes), leads to the common (but mistaken) notion that mirrors reverse right-left. -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw
buchbind@agrigene.UUCP (06/01/85)
> This has more to do with clear thinking than with physics, but here goes: > > When you look in a mirror, the image you see is reversed left to right. > Why is it not also reversed in the vertical direction? > > -- Carl The image is reversed front to back, not left to right. If you are facing North your image is facing South while your Left arm points West in the image and in reality; ditto Right arm and East. -Barry -- Barry Buchbinder 5649 E. Buckeye Rd. Madison, WI 53716 (608)221-5000 {seismo,ihnp4,harpo}!uwvax!astroatc!nicmad!agrigene!buchbind
jeff@rtech.UUCP (Jeff Lichtman) (06/01/85)
> This has more to do with clear thinking than with physics, but here goes: > > When you look in a mirror, the image you see is reversed left to right. > Why is it not also reversed in the vertical direction? > > -- Carl A mirror does not reverse left and right. It reverses front and back. Every part of the object being reflected that is on the left will appear on the left side of the image. The same is true of the right. The mirror image will have the opposite *handedness* as the object being reflected, but this is because front and back are reversed, not because left and right are reversed. -- Jeff Lichtman at rtech (Relational Technology, Inc.) aka Swazoo Koolak {amdahl, sun}!rtech!jeff {ucbvax, decvax}!mtxinu!rtech!jeff
dgary@ecsvax.UUCP (D Gary Grady) (06/03/85)
carlc@tektronix.UUCP (Carl Clawson) asks... (knowing the answer) > When you look in a mirror, the image you see is reversed left to right. > Why is it not also reversed in the vertical direction? But it DOES reverse in the vertical direction, if the mirror is on the ceiling. I'm sure because I just went into the bedroom and checked. Anyway... Mirrors do NOT in fact reverse left for right. They only reverse fore and aft. Stand in front of a mirror and raise your right hand. The mirror image on the same side of your body (east, say), will go up. If it doesn't, see if the mirror is under warranty. Now note which direction you're facing. If you're facing north, say, your mirror image will be looking southward, and no doubt dreaming of mint julips. The reason text (and people) in a mirror look "backwards" is that it is not normally possible to reverse in only one direction. If you are facing north and you want to face south, you must either rotate about a vertical axis (which means your right arm now points west instead of east) or about a horizontal one (so that you are standing on your head). There is nothing wrong with your body; you are just constrained by the laws of normal space. If you hop up a dimension and turn around with respect to the appropriate axis you can come down a mirror image of your old self and eat and eat and not gain weight. Come to think of it, a mirror CAN reverse right and left if you stand with your side to it... -- D Gary Grady Duke U Comp Center, Durham, NC 27706 (919) 684-3695 USENET: {seismo,decvax,ihnp4,akgua,etc.}!mcnc!ecsvax!dgary
kay@warwick.UUCP (Kay Dekker) (06/05/85)
In article <5377@tektronix.UUCP> carlc@tektronix.UUCP (Carl Clawson) writes: >This has more to do with clear thinking than with physics, but here goes: > >When you look in a mirror, the image you see is reversed left to right. >Why is it not also reversed in the vertical direction? > >-- Carl The image is *NOT* reversed left to right. It *IS* reversed back to front. Just spend a few minutes with pencil and paper to demonstrate this (ie, draw a line representing a mirror, and 'reflect' an object in it - simple optics stuff). Kay. -- "It takes a coward like you to insist that Michael Jackson's nun is living in your computer." "flame" output. ... mcvax!ukc!warwick!flame!kay
steve@kontron.UUCP (Steve McIntosh) (06/05/85)
> > When you look in a mirror, the image you see is reversed left to right. > > Why is it not also reversed in the vertical direction? > > > > -- Carl > However, the usual answer to this problem (pointing out that flipping the image > in the verticle axis rather than the horizontal axis is a convention due to > gravity bias) I find unconvincing. So here is a more convincing (to me) > explaination. I have it on good authority that if your eyes were above and below your nose, instead to the left and right, mirrors would indeed flip in the vertical direction instead of the horizontal. Something to do with incidence angles. Of course to get it to flip both ways, you would need four eyes.
throopw@rtp47.UUCP (Wayne Throop) (06/08/85)
[Hit "n" now, or forever hold your peices] [or, what does a one-eyed person see in a mirror?] > > > When you look in a mirror, the image you see is reversed left to right. > > > -- Carl > > However, ... flipping the image in the verticle axis rather than the > > horizontal axis is a convention due to gravity bias[.] I find [this > > explaination] unconvincing. So here is a more convincing (to me) > > explaination. > > -- Wayne Throop > > I have it on good authority that if your eyes were above and below > your nose, instead to the left and right, mirrors would indeed flip > in the vertical direction instead of the horizontal. Something to do > with incidence angles. Of course to get it to flip both ways, you > would need four eyes. > -- Steve McIntosh Since mirrors don't reverse right-left even when eyes are arranged to the left and right of the nose, I see no reason to conclude that if eyes were arranged vertically up-down would be reversed. I don't know what *you* see when you look in a mirror, but I see this situation (viewed from above): "reality" mirror image left | left | | | back-+-front | front-+-back | | | right | right If up-down were included, it would behave like right-left, and would not be reversed. If you had one eye or a dozen, things would still be the same. If your eyes were arranged vertically, horizontally, inside out, upside down, things would still be the same. If your eyes were backwards, on stalks, or in bony pits, things would still be the same. The illusion of left-right reversal is created by an odd convention. The obvious transform to map "reality" onto "image" is reversal of front-back. Most folks, when looking in a mirror, think of the transform "rotate 180 degrees on the up-down axis and reverse left-right", which also works. An equaly valid (and similarly overcomplicated) transform is "rotate 180 degrees on the left-right axis (ie, stand on your head) and reverse up-down". Of the three given transforms, "reverse front-back" is the simplest, the one involving rotation about the up-down axis is most conventional, and the one involving rotation around the left-right axis is almost never used (and of course there are a slew of other almost-never-used transforms that will perform the perceived mapping). The point of all this is that the arrangement of eyes along the up-down axis wouldn't make the rotation about the left-right axis any more appealing, since the preference for the up-down-axis-rotate transform is rooted in the "gravity bias". That is, because of gravity it is easy to both do and think about rotation around an up-down axis, but hard to do or to think about rotation around a left-right axis. The whole point of this so-called "paradox" is that the initial statement, "When you look in a mirror, the image you see is reversed left to right", is in error. My conclusion is that the above mentioned "good authority" should be sent in for routine maintenance. :-) -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw
steve@kontron.UUCP (Steve McIntosh) (06/13/85)
> > The whole point of this so-called "paradox" is that the initial > statement, "When you look in a mirror, the image you see is reversed > left to right", is in error. My conclusion is that the above mentioned > "good authority" should be sent in for routine maintenance. :-) > -- > Wayne Throop at Data General, RTP, NC > <the-known-world>!mcnc!rti-sel!rtp47!throopw *** REPLACE THIS LINE WITH A MIRROR *** What I was referring to was a set of experiments done (someplace) with various types of optical systems that people would wear until they got used to it. One device flipped everything right to left, one flipped things up and down, one did both, some did kelidescope tricks, and so on... Volunteers would wear these things FOR WEEKS and eventually their minds would get used to what the eyes saw, and everything would go back to what they learned was normal - all they felt was that they were wearing some heavy glasses. My motives in placing what was obviously a silly response were the hopes that someone could point me to this research, which I read once upon a time and dont remember where. (And the fact that I wasn't yet up to my coffee quota that morning.) [[I'm a Hacker! Not a psychologist! :- ]]