# Shapes of things unknown?

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 599915.  Sun Aug 16, 2009 10:51 am Actually, that does raise an interesting point - if there was something that existed in more dimensions than we can perceive, I wonder if we would see it but not as it 'really' is.

 599926.  Sun Aug 16, 2009 11:03 am Just a niggle with what Flash said, wouldn't a two-dimensional being encountering a sphere perceive it as a circle, not a straight line? Edit for grammarLast edited by Moosh on Sun Aug 16, 2009 2:35 pm; edited 1 time in total

599975.  Sun Aug 16, 2009 2:20 pm

 Moosh wrote: Just a niggle with what Flash said, wouldn't a two-dimensional being encountering a sphere would perceive it as a circle, not a straight line?
Yes - Otherwise, we'd perceive spheres as circles which we don't - our perception is 3d rich - and I assume flatlanders would have similar 2d perceptual abilities.

Although a drawing/painting/photo would be a line, but with the perceptual cues (eg shading) to allow mr 2d to understand it as a circle.

600049.  Sun Aug 16, 2009 7:17 pm

 Jenny wrote: Actually, that does raise an interesting point - if there was something that existed in more dimensions than we can perceive, I wonder if we would see it but not as it 'really' is.

Which is exactly the stuff that physicists are wrestling with when they discuss the 10/11 dimensional existence. EG Why is Gravity so incredibly weak when compared to the other three fundamental forces? Possibly because the majority of gravitational force is experienced in the higher dimensions which we can't perceive.

600091.  Mon Aug 17, 2009 1:20 am

 Moosh wrote: wouldn't a two-dimensional being encountering a sphere perceive it as a circle, not a straight line?

No, they don't see things in "plan", as though looking at them from above - as they exist only on the surface of the paper, as it were, they see everything sideways-on. They see each other as straight lines as well (of varying lengths, depending on which way they are standing), except for the females which are in fact straight lines, so that they perceive an approaching female as a point.

The bit of the sphere that they can discern is the circle which intersects the plane on which they live - but it's seen sideways-on.

 600096.  Mon Aug 17, 2009 2:18 am I think you're missing the point here, Flash. The key word is perceive. We perceive a hyper-sphere as a sphere - in the same way a flatlander would perceive a sphere as a circle. Even if they lack binocular vision, they could use focus (depth of vision) or movement to spot a circle. Edwin Abbott is plain wrong if he expressed this view back in 1884 - it was intended more as a social commentary (at the time) than anything else.

600107.  Mon Aug 17, 2009 3:04 am

I'm not really making a point, just conveying what it says in the book. Here's the text:
 Quote: I dare say you will suppose that we could at least distinguish by sight the Triangles, Squares, and other figures, moving about as I have described them. On the contrary, we could see nothing of the kind, not at least so as to distinguish one figure from another. Nothing was visible, nor could be visible, to us, except Straight Lines; and the necessity of this I will speedily demonstrate. Place a penny on the middle of one of your tables in Space; and leaning over it, look down upon it. It will appear a circle. But now, drawing back to the edge of the table, gradually lower your eye (thus bringing yourself more and more into the condition of the inhabitants of Flatland), and you will find the penny becoming more and more oval to your view, and at last when you have placed your eye exactly on the edge of the table (so that you are, as it were, actually a Flatlander) the penny will then have ceased to appear oval at all, and will have become, so far as you can see, a straight line. The same thing would happen if you were to treat in the same way a Triangle, or a Square, or any other figure cut out from pasteboard. As soon as you look at it with your eye on the edge of the table, you will find that it ceases to appear to you as a figure, and that it becomes in appearance a straight line.

 600338.  Mon Aug 17, 2009 9:50 am But if you move around the penny, and closer to and away from it, then you'd see it was circular. I think Posital has something on the depth-perception thing as well. If you look at a ball, you can only see a two-dimensional circle, but you can perceive it's three-dimensional by moving around it, and by the shading and so on. I can't see why it would be different for a circle in a two-dimensional world.

 600490.  Mon Aug 17, 2009 4:28 pm I think we're taking an essentially light-hearted book a tad too literally here...

 600497.  Mon Aug 17, 2009 4:41 pm I don't understand what you're disagreeing about. As far as I can tell you all agree that the visual information they get from a circle is a (coloured) line, and from this they infer that the object is a circle. Posital, Flash, Abbot, and Moosh all seem to be saying that very thing. Are you really just disagreeing about which bit should be called "perceiving"? As to the original question, the answer is Quite Interesting. Which is to say that it depends on what the question is. If I may regress a hundred years or so, the Stuff in the Real World is made up of atoms. These are little blobs of mass all joined together. So the shapes we can make in the Real World are, at best, the sort of shapes we can make by joining little blobs together. That pretty convincingly leaves us with lines and curves of various descriptions, however many dimensions they might happen to sit in. Mathematics, on the other hand, has some other things to try. Not satisfied with what the Real World has to offer, nineteenth century mathematicians thought up some alternatives. Consider Peano's space filling curve - that is, a one dimensional line twisted up so it completely fills an area. Or Koch's snowflake, which is an infinitely long line which bounds a finite area. These days such things rejoice under the collective (but not terribly specific) name "fractal". They really don't have to be made of curves or straight lines in any normal sense.

600542.  Mon Aug 17, 2009 6:52 pm

 Jenny wrote: I think we're taking an essentially light-hearted book a tad too literally here...
But it's (laughingly) cited in the case for the defence, m'lud.

 600544.  Mon Aug 17, 2009 6:54 pm I'm not disagreeing (or agreeing) about anything, with anybody. I'm mentioning a book.

 600566.  Mon Aug 17, 2009 7:35 pm Indeed you are mentioning a book. I don't think anyone disputes the text of that book or your summary of what it says. It's just that it seems a little narrow in it's outlook, and not really an authority to be cited on dimensional musings. There was a follow-up book written in the 1970/80s (IIRC) that goes into this more rigorously - that would probably be better to cite. But google/amazon have let me down. Perhaps it was a magazine article - arggh, those little grey cells. Even that book/article had a number of holes in it... not wormholes, mind. It had some interesting asides on the design of doors and locks.

 600568.  Mon Aug 17, 2009 7:47 pm Is it any of these? http://en.wikipedia.org/wiki/Flatland#Related_works

 605005.  Fri Aug 28, 2009 5:23 pm NS on dimensions.

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