"There's this big, ugly sucker at the door," the young woman says, her eyes twinkling, "and he said, 'Who do you think you are, Lena Horne?' I said no but that I knew Miss Horne like a sister."

It's the beginning of a short soliloquy from Walton Jones' play The 1940's Radio Hour, and as she continues with the monologue it's easy to see that the young woman knows what she's doing. Her smile grows while she goes on to recount the doorman's change of tune—like she's letting you in on the joke. Her lips curl as she seizes on just the right words, playing with their cadence. Her expressions are so finely calibrated, her reading so assured, that with the dark background behind her, you'd think you were watching a black-box revival of the late-’70s Broadway play.

There's only one problem: Her body disappears below the neck.

Yaser Sheikh reaches out and stops the video. The woman is a stunningly lifelike virtual-reality avatar, her performance generated by data gathered beforehand. But Sheikh, who heads up Facebook Reality Labs' Pittsburgh location, has another video he considers more impressive. In it, the same woman appears wearing a VR headset, as does a young man. Their headsetted real-life selves chat on the left side of the screen; on the right side, simultaneously, their avatars carry on in perfect concert. As mundane as the conversation is—they talk about hot yoga—it's also an unprecedented glimpse at the future.

For years now, people have been interacting in virtual reality via avatars, computer-generated characters that represent us. Because VR headsets and hand controllers are trackable, our real-life head and hand movements carry into those virtual conversations, the unconscious mannerisms adding crucial texture. Yet even as our virtual interactions have become more naturalistic, technical constraints have forced them to remain visually simple. Social VR apps like Rec Room and Altspace abstract us into caricatures, with expressions that rarely (if ever) map to what we're really doing with our faces. Facebook's Spaces is able to generate a reasonable cartoon approximation of you from your social media photos but depends on buttons and thumb-sticks to trigger certain expressions. Even a more technically demanding platform like High Fidelity, which allows you to import a scanned 3D model of yourself, is a long way from being able to make an avatar feel like you.

That's why I'm here in Pittsburgh on a ridiculously cold, early March morning inside a building very few outsiders have ever stepped foot in. Yaser Sheikh and his team are finally ready to let me in on what they've been working on since they first rented a tiny office in the city's East Liberty neighborhood. (They've since moved to a larger space near the Carnegie Mellon campus, with plans to expand again in the next year or two.) Codec Avatars, as Facebook Reality Labs calls them, are the result of a process that uses machine learning to collect, learn, and re-create human social expression. They're also nowhere near being ready for the public. At best, they're years away—if they end up being something that Facebook deploys at all. But the FRL team is ready to get this conversation started. "It'll be big if we can get this finished," Sheikh says with the not-at-all contained smile of a man who has no doubts they'll get it finished. "We want to get it out. We want to talk about it."