A brief illustrated guide to 'scissors congruence' − an ancient geometric idea that’s still fueling cutting-edge mathematical research
Remember “base x height” for rectangles and “½ base x height” for triangles?
- Remember “base x height” for rectangles and “½ base x height” for triangles?
- But if you were in math class in ancient Greece, you might have learned something very different.
- Ancient Greek mathematicians, such as Euclid, thought of area as something geometric, not algebraic.
Euclid’s notion of area
- So what does it mean to think of area as something geometric the way the ancient Greeks did?
- Using your algebraic formulas for area, you could check that the area of your new shape is equal to the original area of the construction paper.
- In other words, for polygons, Euclid’s notion of area is exactly the same as the modern one.
- Since area is preserved if you cut the pentagon up into smaller triangles, you can instead find the area of these triangles (using “½ base x height”) and add them up to get the answer.
Hilbert’s third problem
- The third problem on the list, and the first to be resolved, is about scissors congruence.
- Dehn’s solution to the problem was very different from the two-dimensional case.
- So, if Dehn could find two polyhedra with the same volume but different values of this invariant, that would prove the answer to Hilbert’s third problem is no – scissors congruence doesn’t precisely capture 3D volume.
- In 1965, Jean-Pierre Sydler confirmed that the answer is yes, closing this chapter on scissors congruence.
Strange shapes and stranger connections
- Mathematics is full of shapes living in higher dimensions – like 4D, 100D, 3,485D or any dimension you can imagine – which are impossible to visualize.
- An active new research area called generalized scissors congruence seeks to uncover whether Hilbert’s question about scissors congruence can also be stated – and maybe even solved – for these strange shapes.
- A recent research program pioneered by mathematicians Jonathan Campbell and Inna Zakharevich proposes a unifying framework for generalized scissors congruence.
- With a little bit of adjustment, mathematicians can harness the machinery of K-theory and apply it to generalized scissors congruence problems.