At the first class of the semester, the professor hopped onto the lecture hall's carpeted stage, the lowest spot in a room with 180 students. Carnegie Mellon University's Luis von Ahn explained why this semester's course would be different. This time, the students would hold new power: They could access lecture notes, posted online, and edit them or rearrange them or clarify them.
As Mr. von Ahn mentioned this, several of the students, laptops open on their desks, were exploring the course's home Web site.
They'd arrived, together, at the class "wiki," a computer forum that allows for unbounded collaborative authoring and editing, revision after revision, and, theoretically, leading to improvement. Though this marks the second time Mr. von Ahn, 27, is teaching great theoretical ideas in computer science, an introductory course required of freshmen computer science majors, it's the first time he's used a wiki.
As with content on Wikipedia, the online encyclopedia open for any Web browser to change, Mr. von Ahn's course material is entirely fluid and indefinite. Students, using a password confirming their enrollment in the class, provide a counter-force to the traditional one-way method of lecturing. Mr. von Ahn acknowledges it's a risk.
"Absolutely," he said recently, while sitting in his office. "The hope is that, after the semester, we'll have lecture notes that have been through one pass, and they'll be that much better than they were before."
For this class, the wiki fulfills both an experimental urge and a need. When Carnegie Mellon University professor Steven Rudich designed the course 15 years ago, no other college in the country offered a similar beginning computer science course, with an emphasis on broad concepts and a de-emphasis of jargon. Because of that, the class has never used a textbook; pieces of six or seven books, Mr. von Ahn said, might cover the course material.
Carnegie Mellon commissioned science writer Ivars Peterson in July 2005 to write the class's textbook. He received, as a starting point, thousands of lecture slides from Mr. Rudich.
Mr. Peterson attempted to convert the dense material of an expert into copy.
"But I couldn't do it entirely on my own," he said.
Carnegie Mellon received from Mr. Peterson a rough outline of 29 lectures. Mr. von Ahn, before giving them, decided on an unorthodox means to improve them.
Before he ever worried about teaching classes, Mr. von Ahn was Carnegie Mellon's computer science prodigy. He developed the ESP Game, now licensed by Google, in which online players, using the ESP Web site, look at pictures of random images and assign them accurate descriptor words. Matching pictures with description helped refine image searches.
The game, like a wiki, channeled the power of a large and willing group of participants.
The Wikipedia entry on Luis von Ahn, which, he says, he never has edited or changed, evidences the wiki's accuracy. The site explains his latest research on CAPTCHAs, the word-identification security system one encounters when, for instance, buying concert tickets online.
It mentions his 2006 MacArthur Fellow award, also called the "genius grant," a $500,000 no-strings attached gift to those showing great creative potential. The site even displays a photograph of Mr. von Ahn, staring from behind a laptop.
Wikipedia, Mr. von Ahn said, "is so much more comprehensive than anything else out there."
But, transferred to a class, a wiki form has altered implications. It tilts the standard classroom dynamic, with the hinted admission that the professor's word doesn't always stand as the final word. It also means that, suddenly, a whole lot of freshmen have a whole lot of say-so.
"I think, in the future, with all these ways of taking information from people in different increments, we'll just be tapping a greater creativity," Mr. Rudich said. "The wiki idea, there are huge amounts of energy with this."
"You can get a lot of different perspectives on the same problem," said Owen Durni, a freshman who helped edit the first lecture. "If I don't find something clear, I'll go in and clarify something."
Mr. von Ahn relishes what he's seen. He planned to discuss in the semester's first lecture "sorting by prefix reversal," a classic math problem best represented with a stack of different-size pancakes and a spatula that can rearrange them by size. When Mr. von Ahn appeared in front of his class, somebody else had edited the wiki and inserted color graphics of pancake stacks.
"By now," Mr. von Ahn said, while sitting recently at his tri-paneled Mac computer, "five people have revised my first lecture. I had first gone over it. The TAs then went over it. We all thought it was perfect. And then we handed it over to the students, and they found 17 errors."
He continued scrolling through other lectures posted on the course site, sometimes months in advance.
"The first lecture now is in great shape. The second one, 'Finite Automata,' has had 14 revisions. You can see here, somebody just edited my lecture from [Jan. 25] three minutes ago. But the lecture I'll be giving today, this one is still rough."
After leaving his office on a recent Tuesday, Mr. von Ahn again met his students, this time for a lecture, "Inductive Reasoning." It was shortly past 3 p.m. Several students, laptops on their desks, followed the day's outline on their screens, primed to edit it if something struck them as unclear or incorrect.
In the next moment, Mr. von Ahn, with a casualness suggesting he didn't expect a battle, mentioned that "zero" qualified as a natural number.
No, students hissed.
They'd been taught natural numbers begin at "one."
Several students raised their hands to add more.
Both a Carnegie Mellon textbook and a famous mathematician, they suggested, believed "zero" did not qualify. In their first semesters of college, most had been taught likewise.
"Well, for the purposes of this class," Mr. von Ahn said, smiling, "we'll define natural numbers as starting with zero, not one!"
Another student spoke out.
"On Wikipedia," he said, "it says both."Steve Mellon, Post-Gazette
Dr. Luis von Ahn, left, chats with Dr. Anupam Gupta and a few students in Mr. von Ahn's office in the Wean Building at Carnegie Mellon University.
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Chico Harlan can be reached at firstname.lastname@example.org or 412-263-1227.