Some of the world’s richest and most powerful people are convinced that we are living in a computer simulation. And now they’re trying to do something about it.

At least two of Silicon Valley’s tech billionaires are pouring money into efforts to break humans out of the simulation that they believe that it is living in, according to a new report.

Philosophers have long been concerned about how we can know that our world isn’t just a very believable simulation of a real one. But concern about that has become ever more active in recent years, as computers and artificial intelligence have advanced.

When the engineers had at last finished their work, Eugenia Kuyda opened a console on her laptop and began to type.

“Roman,” she wrote. “This is your digital monument.”

It had been three months since Roman Mazurenko, Kuyda’s closest friend, had died. Kuyda had spent that time gathering up his old text messages, setting aside the ones that felt too personal, and feeding the rest into a neural network built by developers at her artificial intelligence startup. She had struggled with whether she was doing the right thing by bringing him back this way. At times it had even given her nightmares. But ever since Mazurenko’s death, Kuyda had wanted one more chance to speak with him.