Philip Hopkins, a theoretical astrophysicist at the California Institute of Technology in Pasadena, likes to prank his colleagues. An expert in simulating the formation of galaxies, Hopkins sometimes begins his talks by projecting images of his creations next to photos of real galaxies and defying his audience to tell them apart. “We can even trick astronomers,” says Hopkins, a leader of FIRE, the Feedback in Realistic Environments simulation. “Of course, it's not a guarantee that the models are accurate, but it's sort of a gut check that you're on the right track.”

For decades, scientists have tried to simulate how the trillions of galaxies in the observable universe arose from clouds of gas after the big bang. But in the past few years, thanks to faster computers and better algorithms, the simulations have begun to produce results that accurately capture both the details of individual galaxies and their overall distribution of masses and shapes. “The whole thing has reached this little golden age where progress is coming faster and faster,” says Tiziana Di Matteo, a numerical cosmologist at Carnegie Mellon University in Pittsburgh, Pennsylvania, and a leader of the BlueTides simulation.

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