23 Ağustos 2009 Pazar

When art and math collide


An exhibit of mathematical art reveals the aesthetic side of math


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Mathematics is beautiful: intellectually elegant, exquisitely austere and pretty. Yes, pretty. Like, pretty to look at.

That aesthetic beauty was easy to see at the 2009 Joint Mathematics Meetings in Washington, D.C., January 5–8, which showcased mathematics research and also invited artists and mathematicians to come together to create a display of mathematical art.

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PENROSE TILESUNDERNEATH This shows the pattern of the Penrose tiles at the center of Stacy’s artwork. Artist Paul Stacy made the joints between the tiles invisible when he painted it.

Paul Stacy, an Australian landscape architect, got seduced by the beauty of math when a friend brought him some ceramic Penrose tiles. The tiles don’t seem like much at first glance: they can be one of two diamond shapes, either fat or skinny. But these tiles hold a secret. Put together according to certain rules, they form patterns that never, ever repeat, no matter how far you extend them. Even more surprisingly, they have five-fold rotational symmetry, so you can turn the whole pattern 72 degrees and it will look exactly the same.

Stacy started playing with the tiles to make shapes of his own. He put together nine of the skinny tiles to form a yellow cross on a blue background, and then he did the same with nine of the fat tiles. These larger, nine-tile groups were each the same shape as the individual diamond-shaped tiles that made them up, so Stacy used each nine-tile group as a Penrose tile, following the construction rules of Penrose tiles to create a never-repeating pattern.

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RHOMBIC DODECAHEDRON I:Vladimir Bulatov took inspiration for this sculpture from an unusual polyhedron.Vladimir Bulatov

What emerged was a swarm of groups of blue tiles against a yellow background that seemed to swirl and buzz like a swarm of bees. Stacy discovered that the rules of Penrose tile construction meant there were precisely seven shapes the groups of blue tiles could form. Only long after he finished his piece did he find out that this “discovery” had in fact long been known by mathematicians.

Artist and physicist Vladimir Bulatov builds his artwork like a mathematical proof. He began his Rhombic Dodecahedron I by pondering a funny, irregular looking polyhedron built out of 12 diamond shapes called rhombuses. Bulatov imagined replacing each rhombic face with a sort of four-armed starfish. Instead of connecting the arms directly to those of the closest starfish, he used the symmetries of the polyhedron to interlace the arms, forming an intricate knot.

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THREE-FOLD SYMMETRYThe arms of each "starfish" polyhedron connect at symmetry points. A rhombic dodecahedron has the same symmetries as a cube, and this spot corresponds to the corner of a cube.Vladimir Bulatov

The symmetries of a rhombic dodecahedron, it turns out, are the same as a cube, even though the two are different shapes. Imagine, for example, holding the cube by putting one finger in the middle of a face and the other in the middle of the face directly opposite; you could then keep your fingers still, spin the cube by 90 degrees and have it line up exactly as it was. Your fingers were on either side of an axis of four-fold symmetry. You could do the same with the rhombic dodecahedron.

Because a cube has three pairs of faces, the cube has three axes of four-fold symmetry — and so does the rhombic dodecahedron. In addition, the cube and the rhombic dodecahedron have four axes of three-fold symmetry (if your fingers are on corners of the cube that are diagonally opposite) and six axes of two-fold symmetry (if your fingers are on edges of the cube that are diagonally opposite).

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MONGE’S THEOREMSuman Vaze took inspiration from a theorem in geometry for this painting. Suman Vaze

Mathematically, Bulatov realized, it was possible to twist the faces 90 degrees and weave their arms to meet inside the figure at each of these symmetry points. The question then was: What would it look like?

“I’m a visual person, but I can only rarely imagine my pieces before I make them,” Bulatov says. “I build them like mathematical relationships. For the first time, when I see them on the computer screen, it’s a surprise. I just have to see, does it have aesthetic value?” In this case, the mathematical relationships resulted in an almost magical, twisting, interweaving knot.

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TREFOIL KNOTSThese three knots are different configurations of an overhand knot, called a trefoil. The usual, simplest configuration is on the left. Friedman used the one in the middle as the basis for his sculpture.Nat Friedman

Suman Vaze, a high school math teacher in Hong Kong, takes her inspiration directly from mathematical proofs. In Monge’s Theorem, she illustrates one of the more surprising results in geometry. Take three circles on a plane, any three you like as long as they’re different sizes and none is completely inside another. Connect each pair of circles with two lines that both just touch each edge of the two of the circles. Now consider the three points where each of these pairs of lines intersect one another. It turns out that the points will lie on a single straight line.

Vaze found she couldn’t get this theorem out of her head. “It was like a bee in my bonnet,” she says. “I couldn’t shake it off, so I started doodling.” Her doodles reminded her of the Symphony of Lights, the enormous nightly laser show in Hong Kong, which includes lights from 44 buildings on both sides of Victoria Harbor and is orchestrated to symphonic music “It’s out of this world,” she says. She knew this was a theorem she had to capture in a painting.

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TREFOIL KNOT MINIMAL SURFACEThis is the shape a soap film forms over the simplest knot there is, a trefoil.Nat Friedman

She also loved the simple proof of the theorem: Imagine each circle with its pair of tangent lines as a slice of a cone. There will be two planes that just touch the three cones, and their intersection will form a straight line. The points where the original lines intersect will also lie in the intersection of the planes, and hence along that same straight line.

Nat Friedman, a retired mathematician at the University at Albany in New York, finds intriguing shapes for his sculptures through mathematics. Some of the most profound questions in math concern the most humdrum, everyday objects, like knots and soap bubbles. Friedman combined these by twisting wire to form the simplest knot there is — an overhand knot mathematicians call a trefoil — and then dipping it into soapy water. A film formed across the wire, and he then carved this shape out of limestone. Viewed from some angles, it looks a bit like a yin-yang symbol.

Mathematical art started for Friedman as a side amusement from his mathematical work, but it has come to be a central part of his life. Art, he believes, should be far more central in education. “Learning to see is fundamental to both art and mathematics,” he says. “Whole new worlds open up when you can see better.”

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Mathematician answers Supreme Court plea

New, fair method for dividing states into congressional districts could reduce political squabbles.

In 2003, Republicans in the Texas state legislature proposed a bill that would redistrict the state to increase the likelihood of Republican victories. The Democratic representatives, lacking the votes to defeat the measure, fled the state to deny a quorum. After two standoffs (one lasting 45 days), a Democrat broke down and returned to work, and Republicans pushed the measure through. In the next election, Texas Republicans gained six seats in the U.S. House of Representatives, for a total of 21 seats out of 32.

Democrats sued. The Republicans argued that the new districting was only redressing past wrongs, as Republicans had held fewer than half of the Texas congressional seats, even though they had 57 percent of the vote. In 2006, the case reached the Supreme Court.

“Because there are yet no agreed upon substantive principles of fairness in districting, we have no basis on which to define clear, manageable, and politically neutral standards,” Justice Anthony Kennedy had written two years earlier in a similar case in which the judges upheld the redistricting of Pennsylvania. “If workable standards do emerge … courts should be prepared to order relief.”

In the intervening two years, no such standards had presented themselves. The Texas redistricting was upheld.

The next time a redistricting case goes before the Supreme Court, a mathematician says he can provide a method that may satisfy the court. The solution, says Zeph Landau of the University of California, Berkeley lies in cutting cake.

Politicians figured out the power of redrawing district boundaries back in 1812, when Governor Elbridge Gerry lumped most of the Massachusetts Federalists into a single district, allowing his own part to take control of all the other districts in the state. Newspapers mocked the strange, salamander shaped districts, saying he had “gerrymandered” the state. Oddly shaped congressional districts are now common across the country.

By arranging the boundaries to lose big in a few districts and win the rest by small but safe margins, a party can as much as double its percentage of seats. So if, for example, 40 percent of people in the state voted Democratic, redistricting could in theory make 80 percent of the congressional seats Democratic. If, on the other hand, the Republicans drew the boundaries when they had 60 percent of the vote, they might be able to almost double their percentage and get every last seat, although these theoretical maximums often can’t be realized because of geographical constraints.

So what’s fair?

An entire field of mathematics is devoted to answering just this kind of question. For example, take the classic “I cut, you choose” method of dividing cake: If I cut a cake into two pieces I’d be equally happy with, and you pick which of the two you like better, then neither of us will prefer the other person’s piece to the one we have. The division will be fair in that sense even if our priorities are different. For example, I might really want the rose made of frosting, while you might care only about the size of your piece.

Landau and his collaborators, students Ilona Yershov and Oneil Reid of the City College of New York, realized that the mathematics of fair division could be used to solve the redistricting problem. They used a variation on another cake-cutting method: A third party wields the knife, moving left to right across the cake until one of us calls out, “Stop!” when it seems that both sides are equally good. Then the person who called out gets the left piece and the other gets the right one.

The researchers proposed that a variation of this method be used to divide the state into two regions such that neither political party preferred the other’s region. From there, each party would divide up its own region however it liked.

At first blush, this plan doesn’t seem to solve the problem at all. After all, if one party has only 40 percent of the vote, why should it get a full half of the control of the process of dividing the state into districts?

But the mathematicians showed that equally shared control will lead to about the right outcome even if the parties get very different proportions of the votes. If Democrats get only 40 percent of the vote, they can divide up their half of the state to get at most 80 percent of the seats in that region. If the Republicans get all the seats in their half, that means the Democrats would get about 40 percent of the total seats, which corresponds to their percentage of the total vote anyway.

“The idea is to set up the rules of the game so that cheating isn’t really possible,” Landau says.

Landau points out that any restrictions ordinarily applied to the entire state would continue to be applied to the two half-states. So, for example, districts would continue to be required to have approximately equal populations, and the Voting Rights Act would continue to require that for both half-states, the majority of the population in some districts be ethnic minorities.

This fair division method offers the alluring possibility that each party may feel it got the better deal. The reason goes back to the cake: If I care most about the rose made of frosting and you care most about the size of your piece, we each may think our piece superior to the other’s. Similarly, Landau points out, one political party might particularly want to be able to win the district with a stadium in it, while the other party cared more about a district with an important donor.

The team presented its findings in January at the Joint Mathematics Meetings in Washington, D.C., and the research will appear in an upcoming issue of Social Choice and Welfare.

Political scientist David Epstein of Columbia University praised the approach as innovative, but said it’s unlikely to be politically feasible. “The idea that any subset of people is going to have 100 percent dictatorial control of any portion of any state is totally incompatible with the democratic process,” he says. Still, he believes the idea could be useful in other settings, such as perhaps for sharing power within a corporation.

Landau points out that in the current scheme, the ruling party has nearly dictatorial control already, and his scheme assures that that control can’t be used unfairly. “The problem is that the underpinnings of its fairness aren’t quite transparent,” he says. “It requires a paper to explain it.”

What is clear in any case is that a solution is urgently needed. In the 2004 Pennsylvania case, Justice David Souter remarked, “The increasing efficiency of partisan redistricting has damaged the democratic process to a degree that our predecessors only began to imagine.”

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