Flickr, Delicious (social bookmarking), Answers (reference), and LinkedIn (business contacts) to develop a model of network evolution following the preferential attachment model. For all, the number of connections among members drops off exponentially with more degrees of separation, particularly beyond two hops. Two people with a common friend (two hops away) close a triangle and become friends themselves. There were notable differences in new members: Flickr grows exponentially, LinkedIn grows quadratically, Delicious grows superlinearly, and Answers grows sublinearly.

Anthropologist Robin Dunbar has argued a person can sustain about 150 social relationships and that often was the comfortable size of settlements, farming villages, and the tactical unit of the Roman legion, the maniple. On-line social networks with millions of users also work to keep human scale in mind.

At Facebook, users strive to mask the immense number of nodes with privacy settings, filters such as People You May Know, and the News Feed that shows on your page what your friends are doing and posting (so you don’t have to search dozens or hundreds of individual pages). The News Feed initially set off howls of protest about privacy concerns, but it turned out to be a key element in making Facebook more manageable and fueling its explosive growth. Just as size and density makes cities vibrant and attractive up to a point, Facebook research scientist Jeff Hammerbacher says, “We’ve noticed that people are more likely to become active users if they enter a dense, active network.”

The Facebook network now com-

prises more than 10,000 servers on a Web tier, about 2,000 servers on a MySQL tier, and about 1,000 servers on a MemCache tier. Every second, the site gets 10 million requests, about 500,000 of which are MySQL queries. Data volume was in the tens of gigabytes per day in early 2006, hit 1TB per day by mid-2007, and continues to grow.

 

“i (almost) look like Brad Pitt” What man doesn’t suck in his gut when a good-looking woman walks by? Online, a user posts his or her best picture, usually in a setting that evokes how the user wants to be perceived, such as placing the Newport Yacht Club or a funky bar in the background. Some users resort to deception. Catalina Toma and Jeffrey Hancock of Cornell University and Nicole Ellison of Michigan State found that when it comes to online profiles on Match.com, Yahoo! Personals, Webdate, and American Singles, 81% of a survey group provided information that deviated from reality. “Deviations tended to be ubiquitous but small in magnitude. Men lied more about their height, and women lied more about their weight, with participants farther from the mean lying more,” they noted. “Overall, participants reported being the least accurate about their photographs and the most accurate about their relationship information.” The fact that you can update your profile if the misstatement becomes too pronounced may promote deception, although “a record of the presentation is preserved.” Because of the asynchronicity of social networking sites, “[Users] can plan, create, and edit their self-presentation, including deceptive elements, much more deliberately than they would in face-to-face first encounters,” they noted. “The re-

duction of communication cues, especially nonverbal and visual cues (with the exception of photographs), spares online daters some of the common predicaments faced by traditional daters trying to make a good first impression.”

According to Hancock, similar misstatements appear in email communications, too, and they may show similarities in phrasing. “We’re looking to see if there are any verbal features that might identify these lies,” he says. Which raises the question: Could a future social networking applet be a profile lie detector?

Toma, Hancock, and Ellison found that the online photograph is the information most likely to be less than accurate. The more accurate the photo, the more honest the person is in his or her other profile information. And the more friends who are aware of the online dater’s profile, the more accurate the photo. But beware of escalation once the first lie gets told. Hancock says, “There will be elevated lying if people suspect others are, too. Lying will still be constrained even in a ‘high-lie environment’—most people do not feel comfortable stating big lies.”

Social networks can even make you a fitter, healthier person. Sometimes. Nicole Ellison of Michigan State, Rebecca Heino of Georgetown University, and Jennifer Gibbs of Rutgers University found some respondents to social network and dating sites underreported their weight, then realized they’d better start losing weight to match their ideal self. One woman lost 44 pounds and said, “I can thank online dating for that.” Take that, Jenny Craig.

 

Bill Howard writes about science and technology from Westfield, nJ.

Theoretical Astrophysics
The Universe’s First Star

For the first time, Japanese and u.s. cosmologists have reliably reproduced the formula of the universe’s first star in supercomputer experiments, Science reports, and the protostar they produced was the catalyst for a primordial sun that rapidly

expanded to 100 times the mass of our sun.

Led by astrophysicist naoki Yoshida of nagoya university and a team of colleagues, the supercomputer simulations of the first primordial stars’ formation are partly based on data from nAsA’s Wilkinson

Microwave Anisotropy Probe. the nAsA probe is analyzing the universe’s oldest light, which has been traveling across the universe for 13. 7 billion years.

Yoshida’s team spent nearly eight years on the experiment, and each simulation took a

month of computer time. Even though the theoretical universe exists only as a set of equations operating in a supercomputer, it has provided critical information about the origins of early stars and may help scientists better understand early star formation.