Scientific Theories

　　In science, a theory is a reasonable explanation of observed events that

　　are related. A theory often involves an imaginary model that helps

　　scientists picture the way an observed event could be produced. A good

　　example of this is found in the kinetic molecular theory, in which gases

　　are pictured as being made up of many small particles that are in constant

　　motion.

　　A useful theory, in addition to explaining past observations, helps to

　　predict events that have not as yet been observed. After a theory has been

　　publicized, scientists design experiments to test the theory. If

　　observations confirm the scientists' predictions, the theory is

　　supported. If observations do not confirm the predictions, the scientists

　　must search further. There may be a fault in the experiment, or the theory

　　may have to be revised or rejected.

　　Science involves imagination and creative thinking as well as collecting

　　information and performing experiments. Facts by themselves are not

　　science. As the mathematician Jules Henri Poincare said,"Science is built

　　with facts just as a house is built with bricks, but a collection of facts

　　cannot be called science any more than a pile of bricks can be called

　　a house." Most scientists start an investigation by finding out what other

　　scientists have learned about a particular problem. After known facts have

　　been gathered, the scientist comes to the part of the investigation that

　　requires considerable imagination. Possible solutions to the problem are

　　formulated. These possible solutions are called hypotheses.

　　In a way, any hypothesis is a leap into the unknown. It extends the

　　scientist's thinking beyond the known facts. The scientist plans

　　experiments, performs calculations, and makes observations to test

　　hypotheses. Without hypothesis, further investigation lacks purpose and

　　direction. When hypotheses are confirmed, they are incorporated into

　　theories.