Back in February, I visited a mathematician friend, and we colored some maps. What happens when mathematics and cartography collide? Some 4-color theorem fun.
![The region of Europe directly surrounding Austria (red) is a real-world example of why it's the 4-color theorem and not the 3-color theorem. Italy can't be colored red, blue, or green without causing problems.](http://www.evelynjlamb.com/wp-content/uploads/2013/03/Italy-ruins-everything.jpg)
The region of Europe directly surrounding Austria (red) is a real-world example of why it’s the 4-color theorem and not the 3-color theorem. Italy can’t be colored red, blue, or green without causing problems.
The 4-color theorem is fairly famous in mathematics for a couple of reasons. First, it is easy to understand: any reasonable map on a plane or a sphere (in other words, any map of our world) can be colored in with four distinct colors, so that no two neighboring countries share a color.
Second, computers were instrumental in the proof of the four-color theorem. The theorem had been suggested in 1852 as a conjecture, but people were unable to prove it until 1976, when Kenneth Appel and Wolfgang Haken reduced the problem to a number (1936, to be precise) of specific cases and wrote a computer program to check each case. It was the first major theorem to be proved using a computer, and for some people, it raised questions about what it means to prove a theorem. Did this computer proof “count?” Were mathematicians going to be obsolete soon? People are still debating the role of computers in mathematical proof and the future of mathematics as a human endeavor.
Read the full post at Roots of Unity.
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