Monday, December 15, 2008

Did You Know...

When you see the moon on the horizon, and it seems much, much larger than normal, your mind is playing a trick on you. Your mind is making it look bigger. I wonder if that phenomenon can be applied to the appearance of one's nose in the mirror?

However, many scientists don't like the idea of the "mind" playing tricks on rational man, (when he's not smoking or drinking something) especially if he knows it is a trick but can't do anything about it. Therefore, the debate still goes on as to why the moon looks larger on the horizon...

Any of my scientist readers care to explain this further?

16 comments:

Bill Hensley said...

Perceptually size is always linked to distance. Things that are farther away appear smaller. One explanation for the moon illusion is that we tend to think of things on the horizon as farther away than things overhead. Therefore the moon appears larger when it is on the horizon. Do you buy that?

Here's another one to twist your brain. We know that a mirror shows us an image that is reversed compared to the true object. So why is it always reversed left-to-right instead of top to bottom? Why don't things look upside down in the mirror?

Chaotic Hammer said...

Here's a pretty good page discussing what Bill is saying:

http://www.howstuffworks.com/question491.htm

It even has a little picture with an object you can move around to see the effect for yourself.

Tully said...

I think this is just a guy thing...they often seem to have this issue! :)~

majorsteve said...

Bill, if you take a mirror and put it on your ceiling things will look upside down.

Seth Ward said...

I love you guys!

Bill Hensley said...

But, majorsteve, even if the mirror is on the ceiling, how come that guy in the mirror has his left hand where is right should be instead of his head where his feet should be? (There's a bit of a hint in that question.)

majorsteve said...

Since a mirror is a two dimensional surface it only reverses two of the three spatial dimensions. If situated vertically the right/left and front/back dimensions are reversed. When situated horizontally the up/down and right/left dimensions are reversed. Now you can place a mirror vertically and over to your right or left side, however when you turn to look at it it's suddenly in FRONT of you again.

I can't believe we are having this conversation ;)

Bill Hensley said...

Actually, the question I was hoping to intrigue someone with (besides myself) is why, no matter what the orientation of the mirror is, my image in the mirror is identical to me except that the left and right sides are reversed? Why is that always true regardless of how I am situated with respect to the mirror? And the answer, again, is an anthropic perceptual issue. We perceive the mirror images of humans as having their left and right sides reversed because human bodies are bilaterally symmetric. We implicitly perform the mental rotation to conform the image to our body and find that it maps exactly (ear for ear, eye for eye, foot for foot, hand for hand) except that the left and right sides are reversed.

Seth Ward said...

This is all incredibly fascinating... seriously! Now, like you are talking to a two-year-old. (I think I get it, but I want to be sure.) Is this what you guys are saying?:

That the mind only switches certain things in the mirror? And that might change from where you are positioning the mirror?

What I'm not getting is what is the difference in setting a mirror horizontal or vertical... are you talking about rectangular mirrors... you lost me a little there major..

I'm seriously intrigued, I just want to make sure I'm getting it..

majorsteve said...

Bill and I are talking about two different things. Let me explain it this way: Right and left have no real meaning except for people, that’s the anthropic part. If three dimensional space is like a room with a top (ceiling), bottom (floor), north, south, east and west then the terms right and left are merely anthropic inventions. I look at the guy in the mirror; I point to the west, he points to the west, I point up, he points up, I point forward, he points forward., I point down, he points down. There’s no confusion.

I was talking about the fact that a mirror is a two dimensional surface, and for observers it appears to reverse two out of three spatial dimensions. When the mirror plane is oriented vertically, on one wall of the room, it appears to reverse all dimensions except the up/down, top/bottom, floor ceiling. For example: I look at the guy in the mirror, I move my right hand and the hand he moves is to his left but to my right. I point to a spot behind me but he points to a spot that is behind him but is in front of me. I look down and he looks down. See? That’s two out of three. Now take the mirror and place it on the ceiling, with the plane oriented horizontally, Now I look up, I move my right hand and he moves his left hand,. I touch the floor below me and he touches the surface that is below him but is above me. But when I point to the west he points to the west. Now in the first example I pointed down and he pointed down. In the second example I pointed to the west and he pointed to the west. Therefore, the dimension that didn’t reverse changed in relation to the mirror’s orientation. Lastly, instead of a two dimensional flat plane mirror, consider a three dimensional concave mirror. It actually reverses the up/ down. When you look into a concave mirror even the up/down are reversed. That is a three dimensional mirrored surface reversing all three dimensions of space.

Chaotic Hammer said...

Sorry, but I agree with Bill's explanation more than majorsteve's. (Or perhaps I'm missing majorsteve's point.)

I think the point is that we are bilaterally symmetrical. So the whole thing is merely a trick of our mind, because we're accustomed to thinking in terms of our left and right sides. You could say that our two sides are "mirror images" of one another. So the "mirror" trick is already built in to our biology, before you ever see your reflection in glass. It's an on-the-fly adjustment to perceive that the man in the mirror is punching with his left hand when I punch with my right. But those concepts exist only to make a standard differentiation biologically and functionally.

Think of it another way: We've all seen that fun and silly trick that somebody does along the edge of a mirror (or with a special effect on a video device), where they hide half their body behind the mirror and pretend to pedal a bike or do something silly. It looks to the observer like a full body engaging in a silly motion, but it's actually only half the body, split along the spinal cord, which just happens to be the dividing point in our bilateral symmetry.

You couldn't do this same trick with the mirror across your belly, because then you would look like a being with a chest, arms, and head sticking out on both the top and bottom -- which is not our natural biological arrangement. So it works left to right, but not top to bottom.

To remove the confusing relationship to up and down from the equation, we could do one more thing. Somebody outside the building with heavy machinery could lift up the whole building and turn it 90 degrees, and the person standing inside looking at the mirror can stand on the wall, instead of the floor. But the "camera", or "audience", or "point of reference" remains glued to the floor. (See this cool old clip of Fred Astaire for an example of this). To the guy standing on the wall now, his left and right are still reversed in the mirror! But to us, his stationary audience, his "up" hand is still up and his "down" hand is still down. They don't appear to be "reversed" from our perspective.

One thing that is completely unrelated to all this, but throws a fun twist in, is the fact that the retinas in our eyeballs actually "see" everything completely upside down. It's a perceptual adjustment in our brain that turns these images right side up so that they are correctly oriented to the world around us.

majorsteve said...

CHam, you are right that Bill's answer is right. It can be summed up like this: The terms right and left exist independently of the cardinal directions. I love overcomplicating things. It’s a hobby of mine.

Check this out: This morning I looked in my mirror. I pointed up and the guy in the mirror pointed up. I pointed down and he pointed down. I pointed to the west and he pointed to the west. I pointed to the east and he pointed to the east. But when I pointed to the north he pointed to the south. A mirror only reverses ONE thing, not two. I'm surprised no one called me on that one.

Chaotic Hammer said...

majorsteve - With your very last example, we've actually arrived at the real truth of all this: There is no man in the mirror, and there's nobody pointing anywhere, except you. :-)

The mirror is providing perfectly linear and predictable "output" based on the manner that the light reflects off it. It's only our mind that assembles the reflected light into images and concepts, and applies concepts of relative spacial relationship and direction to the process. If we didn't have this grid mentally overlaid onto the world around us, we would all go bonkers, and be unable to function at the most basic level.

Suppose you were looking into a flat screen that acts as a mirror, but then the "mirror" capability is turned off and it becomes a TV screen. You are still looking at light-based representations of objects that aren't really there at all. We don't see the people on TV as having their left and right reversed, because we're not superimposing the idea that they are "us" looking back from another "realm". We imagine them to be behaving just like they would if there were really people on the other side of the wall, or if the TV were a window instead.

So you're dealing in the realm of perception, not physics. The physics behind what is happening here are consistent, unchanging, and linear.

Bill Hensley said...

Very well put, majorsteve. It is interesting to note that the dimension we perceive as reversed is related to the type of symmetry the object has. For the human body left and right are reversed because we are bilaterally symmetrical. For an object with radial symmetry (like a swastika) the rotational direction is reversed: clockwise becomes counter-clockwise. Objects with rotational symmetry (a wine glass, for instance) appear unchanged when viewed in the mirror. I'm still thinking about that last example and why it is true. I think rotational symmetry is of a higher order because it involves two dimensions, not just one. Major and CHam, can you help me out on this one?

Seth Ward said...

This is one of my favorite conversations thus far on this blog! I've learned quite a bit that I did not know. Thanks fellas!

majorsteve said...

Well guess what...this morning I looked at that guy in the mirror, I moved only my left hand and he moved HIS left hand! How did that happen? It's because the term "left" can be described as being on the same side of the body as the stomach. I moved the hand on my stomach side and he moved the hand that was on HIS stomach side. That's how I know he moved his left hand. In fact, that's how one would described "right" and "left" to a non-humanoid alien. The left side is toward the side of our body that contains the stomach, the "right" side is toward the side of our body that contains the liver organ.