Expert opinion A scientific model is a physical, mathematical, and/or mental representation of an idea, event, or process system. Scientists attempt to find and comprehend patterns in our environment by applying scientific knowledge to provide explanations that allow the patterns to be anticipated. Science is defined as the study of such patterns and their behavior. The word "model" comes from medieval French meaning "something copied after or like another thing," and later applied to diagrams used by geometers to explain concepts in geometry. Today's scientists use models to understand how things work at a deep level, without actually performing the experiments needed to verify their ideas. Models are very useful tools for scientists to explore different possibilities and select the most appropriate one. Models can be theoretical or practical. Theoretical models are derived from observations or experiences and often try to explain some aspect of nature or reality. They may also be used to make predictions about what will happen if certain actions are taken. Practical models are used to simulate natural phenomena or explain the workings of instruments. Scientists use them to explore possible outcomes of choices involving factors that are difficult to control in nature or laboratory experiments. Scientists usually start with a hypothesis which is a proposed explanation for some phenomenon or observation. Then they test it using evidence collected during research. If the results show that the hypothesis is correct, then they expand on it or develop it into a new theory.