## Donald Sampson and Dr. Gary Lawlor, Mathematics Education

### Goal/Purpose

My project was to further develop the technique of metacalibration, a new method of minimization proof, leading to a proof of the triple bubble conjecture: that the standard triple bubble is the least surface area way to separately enclose three given volumes.

### Importance of Purpose

Over the past few decades, mathematicians have become increasingly interested in “multiple bubble problems.” These problems ask which figure among all those that separately contain a given number of volumes has the least surface area. It is conjectured that the minimizer is the standard shape that soap bubbles form when clumped together. Unfortunately, this has been proven only in some few cases. The traditional approach has been to use calculus of variations to isolate properties of the area-minimizing figure and compare all possible figures of this type. Some advancements in planar multiple bubble problems were made by Frank Morgan, who showed that perimeter-minimizing figures consist of circular arcs meeting at vertices of degree three, forming 120° angles [3]. This reduced the argument to listing all combinatorial types meeting these requirements. Using this result, students of the 1990 SMALL group under Frank Morgan proved that the so-called “standard double bubble” was perimeter-minimizing among all figures separately enclosing two fixed areas [1]. This method was also employed by Wacharin Wichiramala, whose doctoral dissertation proves the corresponding result for three separated areas [5]. Unfortunately, this approach is marred by an ever-increasing combinatorial complexity. For example, Wichiramala’s dissertation had to consider fifty-four possible configurations in order to prove minimization of the standard triple bubble. This complexity proves to be a significant barrier to further results.

The three-dimensional analogs of these multiple bubble problems have proven even more difficult to solve. Schwarz first proved in 1884 that the sphere was surface area minimizing for figures that enclose a fixed volume [4], but was not until 2002 that Frank Morgan and others proved the double bubble conjecture in R3 [2]. The final proof relied largely on the fact that the area-minimizing figure must be a surface of revolution. The triple bubble conjecture in space remains unproven. With no special symmetry, the triple bubble conjecture appears to be exceedingly difficult, if not impossible, to prove using this method.

### My Project

In my research I further developed a new method of proof called metacalibration in order to tackle the as-yet-unproven triple bubble conjecture. Metacalibration is a generalization of previously used calibration techniques and was developed at BYU by my adviser, Dr. Gary Lawlor. While calibration techniques have proven very successful in fixed boundary problems, their applicability to fixed volume constraints has previously been limited. Metacalibration is a new approach to calibration proof that overcomes these limitations. This shift in application allows metacalibration to handle a wider range of problems, including the fixed area or volume conditions of multiple bubble problems. Metacalibrations were first used to give a simple new proof of the planar isoperimetric inequality. These results have been subsequently generalized to show boundary minimization of the n-sphere and to prove the planar double bubble conjecture.

### Progress

My plan for this project was to tackle the triple bubble conjecture as a series of sub-problems. Under a previous ORCA grant, I was able to tackle and solve the first two of these problems. The first was developing a new way to overcome the problems of calibrating multidimensional figures. This was done using the mathematical tool of differential forms to generalize our previous two-dimensional results into arbitrary dimension. Using this approach I also completed the next step: generalizing our proof of the double bubble to higher dimensions. This proof combined the principles found in my previous proof of the double bubble conjecture in the plane and the new differential form approach to metacalibrations mentioned above. Considering that the original proof of the double bubble conjecture in space took some twelve years to develop, producing a new and simpler proof of this result was a sizable achievement.

Under this year’s grant, my advisor and I developed conjectural solutions to the last two obstacles to proving the triple bubble conjecture in space. First, we have a plan to solve the triple bubble conjecture in the plane using a metacalibration approach, based on an idea from a proof by E. Shmidt. We hope to complete this proof in the next year. Secondly, Dr. Lawlor has also addressed the problem of generalization to higher dimensions. Given a suitably general solution in the plane, his method should give a proof in three or more dimensions. While the ultimate goal of this project is to prove the triple bubble conjecture, it is hoped that the advancements made in metacalibrations theory will provide a base from which to tackle other unsolved problems in mathematics, and to simplify the proofs of those that have already been solved.

### Citations

- Joel Foisy, Manuel Alfaro, Jeffrey Brock, Nickelous Hodges, and Jason Zimba, The

standard double soap bubble in R2 uniquely minimizes perimeter, Pacific J. Math. 159 (1993)

47-59. - Michael Hutchings, Frank Morgan, Manuel Ritoré, and Antonio Ros, Proof of the double

bubble conjecture, Annals of Math. 155 (2002) 459-489. - Frank Morgan, Soap bubbles in R2 and in surfaces, Pacific J. Math. 165 (1994) 347-361.
- Alan Siegel, A Historical Review of the Isoperimetric Theorem in 2-D, and its place in

Elementary Plane Geometry. <http://www.cs.nyu.edu/faculty/siegel/SCIAM.pdf> (20 Oct

2008). - Wacharin Wichiramala, Proof of the planar triple bubble conjecture, J. Reine Angew. Math.

567 (2004) 1-49.