Which ushered in the second generation of dating sites, like eHarmony and OkCupid. In 2000, eHarmony was launched just as some people began to grow frustrated with online personals. The company’s founders decided that users would benefit from, probably even pay for, help navigating the dating process. Sites like OkCupid, founded by four Harvard grads with math degrees, and a new version of Match claimed they had an algorithm, a unique method of narrowing the choices and matching you with the perfect person — what eHarmony calls its “secret sauce.” Matching sites assert that if they learn enough about who you are, your likes and dislikes, they can cross-reference your answers with those of other users and find your soul mate.

Still, nobody really knew whether these compatibility-matching sites worked, and in 2011, Finkel and his colleagues set about trying to find out. Though eHarmony, PerfectMatch, and others did not release their scientific algorithms for study, the academics found a way around the lack of data. They identified the methods that inform these algorithms and compared them with 80 years of psychological findings about long-term compatibility. They quickly realized that many sites rely on an “intuitive but flawed principle” that psychological similarity promotes compatibility. Here’s the rub: Although the perception of similarity makes relationships successful, actual commonalities are largely irrelevant. For example, if you meet someone and think you’re similar to them, then you have a good chance at starting a relationship. But simply having things in common — boating, openness to new experiences, desire for a traditional family — does not give two people a greater chance of connecting. The distinction is critical. Says Finkel, “Their theory of relationship success is predicated on a house of cards.” 

 When the iTunes app store launched in July 2008, online dating seemed once again to be morphing: Singles wanted to date on the go, and technology was making it possible. And thus began the third generation of dating sites and the new era of mobile dating. “Mobile dating has created a new promise, an enticing one,” says Aaron Schildkrout, who grew up in Newton and cofounded HowAboutWe, which has a location-based dating app. “When you see these people on your phone, you think, ‘This person is real, they’re near me, and I may actually be able to encounter them in the real world.’ ”

 In 2009, Grindr, a location-based dating app catering to gay men, exploded onto the dating scene everywhere from Province-town to the West Village. Grindr was the first app of its kind to get traction — a real-time dating app that allowed people to meet up instantaneously based on proximity. Suddenly it became easy to find out who else was gay, single, and steps from your front door. By March 2012, Grindr had 4 million users in 192 countries.

“It was so wildly popular,” says Serge Gojkovich, who helped launch Grindr, that “everyone was asking us why don’t we have a similar site for straight people?” In 2011, he helped launch Blendr, an online dating site and mobile app designed to help people of all sexual orientations find the same spontaneous trysts as Grindr offers. Several other location-based mobile apps catering to straight singles launched around the same time. MeetMoi, which came online as an iPhone and Android app in 2010, alerts users when another MeetMoi user is nearby. SinglesAroundMe, also released in 2010, features a singles-locator map of sorts; when you open the app, multiple pins drop onto the map, each indicating another single nearby. OkCupid launched its Locals app in 2011, giving users the chance to meet up with singles close by, and HowAboutWe’s location-based app, which came on the scene in 2011, shows date suggestions from people within several blocks of you if you’re accessing the app from a major city like Boston.