a lower-energy configuration by rolling up first and then down, but it is not observed to do so.  A poster named Craig Feinstein replied to these skeptics as follows [@feinstein:soap]:

> Have experiments been done to show that it is only a local minimum that is reached by soap bubbles and not a global minimum or is this just the party line?  I’d like to believe that nature was designed to be smarter than we give it credit.  I’d be willing to make a gentleman’s bet that no one can site \[sic\] a paper which describes an experiment that shows that the global minimum is not always achieved with soap bubbles.

Though I was unable to find such a paper, I was motivated by this post to conduct the experiment myself.[^4]  I bought two $8\textquotedblright\times9\textquotedblright$ glass plates, paint to mark grid points on the plates, thin copper rods which I cut into $1\textquotedblright$ pieces, suction cups to attach the rods to the plates, liquid oil soap, a plastic tub to hold the soapy water, and work gloves.  I obtained instances of the Euclidean Steiner Tree problem from the OR-Library website [@beasley].  I concentrated on instances with $3$ to $7$ vertices, 