Computers have a great many functions, but for scientists it is often their power of simulation that is used. Supercomputers are used to simulate almost anything from the weather to subatomic interactions, because this allows us to study systems too complex to observe all the variables of, and with far greater detail than modern techniques allow. This capability of computers has led some to speculate if maybe we are living in a computer simulation right now, but researchers at the University of Washington have devised a way to test this hypothesis.
The premise to us living in a simulation is simple enough: a post human civilization has created this extremely accurate simulation to learn about their ancestors (us). Of course such a simulation would require computing power far beyond what is currently possible, but we can guess how such a simulation would be constructed, which should enable us to test if we are within one. Assuming the simulation is based on a four dimensional grid, which allows it to represent the strong force that holds atomic nuclei together, then there should be signature left on cosmic rays. This signature would be inappropriate behavior by cosmic rays due to the imperfections of such a 4D system.
If it turns out that we really are in a simulation the next question the researchers will ask is if we are alone or if other simulations are running on the same computer system. At that point cross-simulation-communication will be on the agenda. That is assuming this simulation would not simply be ended, because of the unnatural awareness of the simulation which will invalidate its results.