contributed articles Doi:10.1145/1924421.1924441 how more recent developments (such Finding 10 balloons across the U.S. illustrates as social media and crowdsourcing) could be used to solve challenging how the Internet has changed the way problems involving distributed geo- we solve highly distributed problems. locations. Since the Challenge was an- nounced only about one month before By John C. tanG, manueL Cebrian, nicklaus a. GiaCoBe, the balloons were deployed, it was not hyun-Woo Kim, taemie Kim, anD Douglas “BeaKeR” WickeRt only a timed contest to find the bal- loons but also a time-limited challenge to prepare for the contest. Both the dif- fusion of how teams heard about the Challenge and the solution itself dem- Reflecting onstrated the relative effectiveness of mass media and social media. The surprising efficiency of apply- ing social networks of acquaintances on the DaRPa to solve widely distributed tasks was demonstrated in Stanley Milgram’s celebrated work9 popularizing the no- tion of “six degrees of separation”; that is, it typically takes no more than six in- Red Balloon termediaries to connect any arbitrary pair of people. Meanwhile, the Internet and other communication technolo- gies have emerged that increase the Challenge ease and opportunity for connections. These developments have enabled crowdsourcing—aggregating bits of information across a large number of users to create productive value—as a popular mechanism for creating en- cyclopedias of information (such as ThE 2009 dARPA Red Balloon Challenge (also known Wikipedia) and solving other highly distributed problems.1 as the DARPA Network Challenge) explored how the The Challenge was announced at the Internet and social networking can be used to solve “40th Anniversary of the Internet” event a distributed, time-critical, geo-location problem. (http://www.engineer.ucla.edu/IA40/ index.html). On December 5, 2009, at Teams had to find 10 red weather balloons deployed 10:00 a.m. Eastern time, 10 numbered, at undisclosed locations across the continental U.S. eight-foot-diameter red weather bal- The first team to correctly identify the locations of loons were deployed at moored loca- all 10 would win a $40,000 prize. A team from the key insights Massachusetts Institute of Technology (MIT) won in Crowdsourcing, social networking, and traditional media enabled teams less than nine hours (http://networkchallenge.darpa. to quickly find 10 weather balloons mil/). Here, we reflect on lessons learned from the scattered across the u.s. a Besides finding the balloons, P strategies used by the various teams. dar distinguishing correct balloon sightings F The Challenge commemorated the 40th anniversary from misleading claims turned out to be an important part of the effort. of the first remote log-in to the ARPANet (October 29, Variations in the strategies of the h courtesy o P competing teams reflected differences ra 1969), an event widely heralded as the birth of the G in how social media can be tailored Internet. The Challenge was designed to identify to fit a given task. Photo 78 CommuniCations oF the aCm | April 2011 | vol. 54 | nO. 4 tions across the continental U.S. (see each balloon and an attendant at each fied the location of all of them in eight Figure 1). DARPA selected readily ac- balloon issuing certificates). Teams hours, 52 minutes, 41 seconds. A team cessible public sites where the balloons submitted their guesses to a DARPA from the Georgia Tech Research Insti- would be visible from nearby roads, Web site and were given feedback as to tute (GTRI) placed second by locating each staffed by a DARPA agent who which balloons had been identified cor- nine balloons within nine hours. Two would issue a certificate validating each rectly. While the balloons were sched- more teams found eight balloons, five balloon location. While general infor- uled to be taken down at 5:00 p.m. local teams found seven balloons, and the mation about the Challenge (such as time, DARPA was prepared to re-deploy iSchools team (representing Pennsyl- date and time of the deployment, with them a second day and leave the sub- vania State University, University of a picture of a balloon) had already been mission process open for up to a week Illinois at Urbana-Champaign, Univer- distributed, some details were not an- until a team identified all 10. sity of Pittsburgh, Syracuse University, nounced (such as DARPA’s banner on The team from MIT correctly identi- and University of North Carolina at april 2011 | vol. 54 | nO. 4 | CommuniCations oF the aCm 79 contributed articles platform for viral collaboration that used recursive incentives to align the public’s interest with the goal of win- ning the Challenge. This approach was inspired by the work of Peter S. Dodds et al.5 that found that success in us- ing social networks to tackle widely distributed search problems depends on individual incentives. The work of Mason and Watts7 also informed the use of financial incentives to motivate crowdsourcing productivity. The MIT team’s winning strategy was to use the prize money as a finan- cial incentive structure rewarding not only the people who correctly located balloons but also those connecting Figure 1. Locations in the DaRPa Red Balloon Challenge. the finder to the MIT team. Should the team win, they would allocate $4,000 Figure 2. example recursive incentive-structure process for the mit team. in prize money to each balloon. They promised $2,000 per balloon to the first person to send in the correct Alice wins $750 ALICE balloon coordinates. They promised Bob wins $500 $250 $1,000 to the person who invited that Carol wins $1,000 $500 balloon finder onto the team, $500 Dave wins $2,000 to whoever invited the inviter, $250 to whoever invited that person, and so on. Any remaining reward money would be donated to charity. BOB $1,000 $500 Figure 2 outlines an example of this recursive incentive structure. Alice joins the team and is given an invite link, like http://balloon.mit.edu/alice. Alice then emails her link to Bob, who Another CAROL balloon uses it to join the team as well. Bob $2,000 $1,000 found! gets a unique link, like http://balloon. mit.edu/bob, and posts it on Face- book. His friend Carol sees it, signs up, then twitters about http://balloon.mit. edu/carol. Dave uses Carol’s link to dAvE Balloon $2,000 join, then spots one of the DARPA bal- found! loons. Dave is the first person to report the balloon’s location to the MIT team, helping it win the Challenge. Once that happens, the team sends Dave Chapel Hill) finished tenth by locating balloon sightings, and the role of so- $2,000 for finding the balloon. Carol six balloons. cial networking tools in their process. gets $1,000 for inviting Dave, Bob gets Two months later, at the Comput- While the GTRI team was unavailable $500 for inviting Carol, and Alice gets er-Supported Cooperative Work Con- for this article, we report on what they $250 for inviting Bob. The remaining ference (http://www.cscw2010.org/) shared at the CSCW session and pub- $250 is donated to charity. in Savannah, GA, a special session lished elsewhere.6,11,12 The recursive incentive structure dedicated to lessons learned from the differed from the direct-reward op- Challenge brought together represen- mit team tion of giving $4,000 per balloon tatives from the winning MIT team, The MIT team learned about the Chal- found in two key ways: First, a direct the GTRI team, and the iSchools team lenge only a few days before the bal- reward might actually deter people to compare and contrast among the loons were deployed and developed a from spreading the word about the strategies and experiences across the strategy that emphasized both speed MIT team, as any new person recruit- teams. There, members of the MIT (in terms of number of people recruit- ed would be extra competition for the and iSchools teams reflected on their ed) and breadth (covering as much U.S. reward. Second, it would eliminate strategies, how they validated their geography as possible). They set up a people living outside the U.S., as there 80 CommuniCations oF the aCm | April 2011 | vol. 54 | nO. 4 contributed articles was no possibility of them spotting a used involved comparing the IP ad- Many submissions included pic- balloon. These two factors played a dress of the submission with where tures, some contrived to confirm mis- key role in the success of the MIT ap- a balloon was reported found; for ex- leading submissions. Most altered pic- proach, as illustrated by the fact that ample, one submission reporting a tures involved shots of a balloon from the depth of the tree of invites went up balloon in Florida came from an IP ad- a distance and lacked the DARPA agent to 15 people, and approximately one dress in the Los Angeles area. A simple holding the balloon and the DARPA of three tweets spreading information IP trace and common sense filtered banner (an unannounced detail). Fig- about the team originated outside the out such false submissions. ure 4 shows examples of authentic and U.S. Distributing the reward money more broadly motivated a much larger Figure 3. typical real (top) and false (bottom) locations of balloons, with bottom map depicting five submissions with identical locations. number of people (more than 5,000) to join the team, including some from outside of the U.S. who could be re- warded for simply knowing someone who could find a balloon. This strategy combined the incentive of personal gain with the power of social networks to connect people locating each bal- loon with the MIT team.