An Impossible Construction

Published by patrick honner on

I enjoy offering impossible problems to students as extra credit, although I usually don’t tell them the problems are impossible.  Such tasks usually engage them, confuse them, and make them suspicious of me.  It’s a win-win-win.

While discussing some three-dimensional geometry, I offered extra credit to anyone who could build a model of a Klein bottle.  The Klein bottle is a hard-to-imagine surface that has neither an inside nor an outside.  It’s like a tube where one end meets the other and makes a seal, but somehow got turned inside out in the process.  If you are familiar with the Mobius strip, the Klein bottle is basically a higher-dimensional Mobius strip.

One reason that the Klein bottle is hard to visualize is that it can’t be observed in three dimensions:  it needs a fourth dimension in order to see it turn itself inside-out.  This is analogous to the standard construction of the Mobius strip:  we take a long strip of paper, give one end a half-twist, and tape the ends together.  We think of the paper itself as being 2-dimensional, but we need that third dimension to twist through.

So, I was pretty impressed with the student who made this.

Klein Bottle
Not bad at all, for someone who is dimensionally challenged.  Here’s a nice representation for comparison, although it’s still a cheat.  The Klein bottle doesn’t really intersect itself.

Klein bottle graph

A nice example of impossibly creative student work!

patrick honner

Math teacher in Brooklyn, New York


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