Last year, on January 18th, I took a screenshot of an e-mail an editor had sent me about a story that I was writing on the traffic conditions in San Jose. I also retweeted a bot that had noted the first use in the Times of the word “cryptocoins.” Three years ago, also on January 18th, I took a photo with two friends from college, one of whom I haven’t seen in a long time. Ten years ago, on Facebook, I posted a status: “um i hate when weekends end.”

I learned this odd assortment of mundane facts from Timehop, an app that claims to be “reinventing reminiscing for the digital era.” Boasting more than twenty million users, Timehop produces neatly packaged time capsules of your online engagement. You can connect it with your Instagram, Facebook, Twitter, Google Drive, Apple Photos, and so on, and Timehop will trawl those platforms for things that happened on this day, however many years ago. The first iteration of the app was created in 2011, at a hackathon organized by Foursquare; it was a daily e-mail that told you where you were when you checked into Foursquare a year earlier. The programmers were surprised by the response to this single piece of information. “You know, just seeing the name of a bar would spark all these crazy emotional memories,” Matt Raoul, the C.E.O. of Timehop, told me. He sees Timehop as a tool for connecting with people, rather than as a platform for insular retrospection. “You know, I open up my Timehop, and I’ll see things on there with friends I may not have talked to for a while, and then I’ll think, I’m going to send this to her,” he said. Our online behavior suggests that he’s onto something; witness the recent #2009vs2019 challenge. Facebook, Apple, Spotify, and other platforms have all entered the business of dredging up the past, betting, along with Timehop, that nostalgia is a socially oriented emotion.

What tech companies are doing is subtly different from classic nostalgia-marketing. Rather than using cultural symbols to trigger collective nostalgia, they’re using you and what they know about you. Spotify is especially good at this. In addition to my “Top Songs of 2018” playlist, Spotify made me a list called “Time Capsule,” relying on my date of birth to create a collection that features songs by Boys Like Girls and Blink-182. It will do the same for anyone, conjuring up your teen-age radio station.

In the most recent version of Apple Photos, there’s a “For You” tab that curates albums of “memories,” using facial-recognition technology along with location and time-based data. If you go to England for a week, expect an album based on your trip. If you take a dozen pictures of a single person, you’ll get a collection of close-ups. Facebook was one of the earliest adopters of nostalgia-trafficking, with posts celebrating friendship anniversaries and things that happened eight years ago today. Last year, the company added more features, so you now get collections like “Your January Memories.” It prompts you to share the post.

This resurfacing of content is often framed in terms of rediscovery, as though, without the algorithms, we might lose track of our own lives under the weight of time. The velocity of social media is overwhelming; perhaps that’s why anything from the recent past can feel so surprising. The app-based nostalgia machine works in a kind of loop, resurfacing ephemera that the algorithm suspects we like, so that we might “like” or post or listen again. It’s a little hard to tell whether these platforms are capitalizing on our collective desire to post a picture of ourselves circa 2009 vs. 2019, or whether we’re taking cues from Facebook Memories. Who decides it’s Throwback Thursday, Instagram or us?

In addition to our curated memories, tech companies are serving up cold, hard metrics, and we seem to want those, too. (Timehop is a bit of an outlier because it doesn’t offer many numbers; Raoul said, “There are parts of that tracking that are really unhealthy.”) Spotify’s “Wrapped” gives you usage stats—you listened for 60,783 minutes per year—which is 7,053 more minutes than you listened last year. Apple’s Screen Time does the same thing, breaking down your phone usage: you were on Twitter for twenty-five minutes yesterday, devoted fifty-seven minutes to Messaging, fifteen minutes to “Reading and Reference.” Apple’s Health app will track your steps; people are increasingly opting into sleep-tracker apps on their phones or Fitbits. Willingly, we give over data in return for simple metrics about our own lives.

Which tell us what, exactly? Looking back on usage metrics doesn’t play to our nostalgia like listening to old songs; these features are almost anti-nostalgic in their hard breakdowns of how we actually spend the days, months, and years of our lives. Jack Dorsey, Twitter’s chief executive officer, provoked ridicule in December when he tweeted a thread about his time at a meditation retreat in Myanmar. Despite claiming that “no devices” were allowed, he wore an Apple Watch and the sleep tracker Oura Ring in airplane mode, and posted his metrics upon his return. “My best meditations always had the least variation in heart rate,” he tweeted. Of his sleep, he wrote, “my resting heart rate was consistently below 40.” In Silicon Valley speak, he’d reached nirvana, or at least he’d relaxed a little bit, and he had the evidence to prove it and post about it.

Dorsey took documenting his habits to its illogical extreme, exposing the fallacies of life viewed retrospectively through the lens of the usage of time. But these metrics continue to appeal to many of us, trapped in the cycle of self-improvement; if we track our time, perhaps we could manage it better next year. Meanwhile, we’ll look and listen back to the past, which has been resurfaced and culled for us. It’s very seductive. The tagline for Spotify Wrapped says it all: “Take a look at how you listened. Because no one listened exactly like you.”