Some types of science can say what could happen many, many years from now. For example, astrophysics can say how planets and stars form, affect each other, and die; particle physics can say how atoms and other matter act over time; evolutionary biology can allow us to see how living things change over time; and plate tectonics can say how continents shift over time. By observing the past and present, astrophysicists, particle physicists, evolutionary biologists and geologists can make good guesses about what might happen in the future. We call these guesses "predictions".