As the fake universes improve, their role also is changing. For decades, information flowed one way: from the astronomers studying real galaxies to the modelers trying to simulate them. Now, insight is flowing the other way, too, with the models helping guide astronomers, says Stephen Wilkins, an extragalactic astronomer at the University of Sussex in Brighton, U.K., who works on BlueTides. "In the past the simulations were always trying to keep up with the observations," says Wilkins, who is using BlueTides to predict what NASA's James Webb Space Telescope will see when it launches in 2020 and peers deep into space and far back in time. "Now we can predict things that we haven't observed."