Before another match, a renegade robot wandered off the field toward the organizers' table, seemingly to greet them—but it was really making a beeline for the nearby orange RoboCup logo banner, which was exactly the same color as the game ball. “Right now, if a robot sees something orange, it thinks it's a ball,” says Ubbo Visser, a local RoboCup chairman who saw the incident. “Humans have a larger background information database, so we say, 'It can't be a ball because it's not in the right context.'”

In addition to programming conundrums, RoboCup designers face nuts-and-bolts physical engineering challenges. In the Humanoid division, which featured two-legged players (robots in other divisions move on four legs or wheels), some gimpy competitors had a hard time staying upright. Spectators tittered at referee verdicts like “There will be no goal because the goalie has fallen down.”

“The problem of balancing on two legs is very tough. The AIBO dog robots have it easier, because they have four legs and more stability,” says Pasan Kulvanit, a member of Team KMUTT from Thailand's King Mongkut's University of Technology. “And you can't even think about your artificial intelligence until you've built a robot with perfect balance.”

Though false starts were common, the bots could seem invincible when they hit a hot streak, mounting scoring drives capped by hot-dog maneuvers that demonstrate just how far robotics has come in the past decade. For top teams like those from Germany, Korea, and Iran, precise lateral passes and spectacular saves were routine game plan components, eliciting loud cheers from the crowd of 15 000 spectators. Even nascent leagues like the Humanoid division logged significant progress. “Last year, almost none of the teams could walk, and this year, a lot of them can,” Kulvanit says. “That's pretty amazing.”

Ideally, according to RoboCup president Minoru Asada, this incremental progress will inspire a generation of robots that can face off against human soccer players and win—a highly specific objective, but one that makes sense given how seamlessly robotics innovations can transfer between fields. Robots designed to perform tasks like aiding senior citizens and retrieving pets from burning homes will need the same flexible thinking skills crucial to soccer success. “If you're able to make a robot that can win against a human [soccer] team, you'd definitely be able to use it to do things like clean rooms and wash windows,” says Frank Sehnke, a member of Tubingen's Attempto squad.

Despite marketing efforts to play up the competition's similarities to the World Cup, the RoboCup was dominated by an entirely different kind of intensity—in part because of its beta-test feel, in part because with such lofty technical objectives on the horizon, the identity of this year's winners seemed beside the point. Host Germany claimed 11 of the 33 gold cups in the offing, with China and Japan close behind, but most behind-the-scenes conversations between players focused on how they planned to upgrade their robot charges, not on how proud they felt to hoist the trophies.

“Everyone knows what soccer is, so that provides a way of communicating these new technologies to the public,” Burkhard says. “But mainly, we want to understand what human intelligence means so that we can create it.”