Scientists have exercised god-like powers by creating an entire universe of their own.
The man-made cosmos is a computer simulation in which galaxies similar to those observed by astronomers grow and evolve.
Two of the world's most powerful supercomputers - the "Cosmology Machine" at the University of Durham and "Curie" in Paris - were used to conduct the simulations, which took several months to run.
Previous attempts to model the formation of galaxies have met with little success, producing collections of stars that were often too massive, small, old or spherical.
Those produced in the Eagle (Evolution and Assembly of Galaxies and their Environments) simulation are much more realistic.
One key to its success is the recreation of galactic winds - cosmic gas gales driven by stars, supernova explosions and supermassive black holes - which are stronger than those in earlier simulations, say the scientists.
Galactic winds affect the development of galaxies by blowing away the gas from which stars form.
The sizes and shapes of the thousands of galaxies produced in the Eagle simulation closely match their "real" counterparts, and can be used to study the history of the universe almost as far back as the Big Bang 13.8 billion years ago.
Professor Richard Bower, from the University of Durham, said: "The universe generated by the computer is just like the real thing.
"There are galaxies everywhere, with all the shapes, sizes and colours I've seen with the world's largest telescopes.
"It is incredible. In the Eagle universe I can even press a button to make time run backwards."
Results from the research will appear in the journal Monthly Notices of the Royal Astronomical Society tomorrow.
Co-author Dr Rob Crain, from Liverpool John Moores University, said: "This is the start of a new era for us. We can now manipulate the conditions of the universe and study the evolution of galaxies throughout the past 14 billion years."