Why don't mirrors invert the image vertically?

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Discussion Overview

The discussion revolves around the question of why mirrors appear to invert images horizontally but not vertically. Participants explore the psychological and perceptual aspects of this phenomenon, as well as the implications of spatial orientation and symmetry in relation to mirror reflections.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that mirrors do not actually reverse images left to right; rather, they reflect the image as it is, with left and right remaining consistent based on the viewer's perspective.
  • Others argue that the perception of left-right inversion is a psychological phenomenon, influenced by how individuals project their consciousness onto the mirror image.
  • A participant describes a scenario where pointing in different directions demonstrates that mirrors do not reverse left and right but instead swap front and back, leading to confusion about the left-right perception.
  • One participant posits that the reason for the perceived vertical stability is due to the inherent nature of up and down being constant, unlike left and right, which can change based on orientation.
  • Another participant presents a diagram to illustrate that the perception of left-right inversion is arbitrary and linked to human lateral symmetry, suggesting that different beings might perceive mirror reflections differently.
  • Some participants contend that mirrors do invert vertically in the same way as horizontally when considering rotations about different axes, although this perspective is not commonly recognized.
  • A participant provides a thought experiment involving the orientation of the mirror to demonstrate that the perceived inversion can change based on how the mirror is positioned relative to the viewer.
  • One participant references Feynman's explanation, emphasizing that the way we conceptualize the movement of the reflection contributes to our understanding of horizontal versus vertical inversion.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of mirror reflections, with no consensus reached on whether mirrors truly invert images or if the perception of inversion is purely psychological. Multiple competing perspectives remain throughout the discussion.

Contextual Notes

Some arguments depend on specific definitions of left, right, up, and down, and the discussion does not resolve the mathematical or physical implications of these perceptions.

interhacker
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I was looking at the hover text of this xkcd comic. It said:

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 tried to answer the question myself for a while and arrived at the conclusion that I'm a brain-damaged nitwit. Then it occurred to me that the best course of action would be to ask people with higher intelligence. So, can any of you explain the reason to me?

Thank you. All the best. :smile:
 
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Why do you think they have reversed left-right? If you raise your left hand the person in the mirror raises a hand on the left side. It does not reverse images left-right. If you are projecting your consciousness into the image of the mirror and pretending that you are looking out of the mirror towards the room then you can think of yourself as reversed... But then you could just as easily pretend you are looking into the wall... Its a psychological phenomenon. You are anthropomorphising or projecting consciousness and perspective onto that which has none. This is easy to do because it looks like a person, but of course we know its not. Its an image that reflects without flipping. What is up reflects on the top, what is on the left reflects on the left.
 
interhacker said:
So, can any of you explain the reason to me?

Suppose you are facing north and standing in front of a mirror. You point a finger to the west and your image points a finger to the west. You point a finger straight up and your image points a finger straight up. You point a finger to the east and your image points a finger to the east. You point a finger down and your image points a finger down. There's no reversal going on so far.

But when you point a finger to the north... Your image points a finger to the south. Come to think of it, although you're facing north your image is facing south. And if you rotated the whole affair, mirror and all, so that you were facing west, then your image would be facing east.

The mirror is reversing the directions that you call "front" and "back"; the left/right thing is just the result of you defining left and right in terms of the direction that you are facing.
 
Fortunately, this question can be answered by one of the greatest :smile: :

 
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Normally when you look at an object in a mirror its left and right sides are swapped with regards to yours, which is why when people shake hands their right hands are diagonal to each other. But a mirror allows you to see that side of an object without having to turn it around and reverse it.

The reason objects don't appear to be reversed vertically is because our world is inherently built with clear-cut down and up directions, but not left-right directions. That is, your left and my left are different depending on which way we are facing, but up and down are always the same no matter which way you turn. We can turn left and right all day long, but you never flip upside down to turn around.

Do this: Take a piece of paper with words on it and flip it upside down in front of a mirror. The words no longer appear reversed, they appear upside down! Similarly, if you and I are standing next to each other, facing the same direction, and I do a handstand, our left and right directions are still the same, but our up and down directions are now reversed!
 
I made this some time ago:
G8FXKNkl.png

It might help visualise what other posters were talking about.

The point of making the diagram was to show that the left-right inversion perception is just as arbitrary as up-down inversion, and the particular preference humans exhibit is likely due to our lateral symmetry. An imaginary creature with an up-down symmetry only would insist that a mirror inverts those two directions, an a creature with no symmetry would probably never even think a mirror could invert anything but the front-back direction.
 
If you are precise, you will find that the mirror does invert vertically in the same matter as it does for left-right. What do we mean to say the mirror inverts left and right? Well, if I rotate the image in the mirror about the z (up) axis and try to line it up with myself, the left and right sides would be switched. Similarly, if I rotate the image about the horizontal axis (the x-axis in the above post), I would find that my head and feet are swapped. But people don't think to make that rotation as much as they do the first one.
 
QuasiParticle said:
Fortunately, this question can be answered by one of the greatest :smile: :



Thank you so much for sharing that excellent video. It finally made me understand. I am also grateful to everyone else for providing wonderful insight on the issue.
 
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  • #10
"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?"

If you take the mirror down from the wall and lay it on the floor. Then place the word on the floor next to the mirror, standing upright. Then sit on the floor opposite the word. And look at the word in the mirror. It will be reversed vertically. But not horizontally. Further, if you stand up and look down, you will see yourself looking upward. With you right hand on the right. Your right, that is to say, your reflections' left.

So, the word was reversed horizontally in the question posed because the mirror was oriented so as to create that effect. It needn't be. There are alternatives.
 
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  • #11
Feynman explains it very well. We imagine that the man in the mirror got to where he is, by starting where we are, and then walking around the mirror, and turning around to face us. Interestingly, we don't imagine that he got there by climbing over the mirror, and then facing us head-to-toe. This is because it is much easier for us to notice the difference between our head and our toes, than the difference between our left side and right side. So horizontal gets mixed up, rather than vertical, because the horizontally incorrect imagination is much closer to the true image than the vertically incorrect imagination.
 

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