Final answer:
A theory may be changed or rejected in favor of a better explanation, signifying that theories evolve over time with new evidence. They are comprehensive explanations, not guesses, and can be revised if new experiments contradict them.
Step-by-step explanation:
The reason a theory may be changed or thrown out is because theories are accepted based on which one will give the BEST explanation. Unlike a scientific law, which describes patterns in large amounts of data and remains quite stable over time, a scientific theory is subject to change. Theories evolve and can be revised or discarded in light of new evidence that provides a better explanation or if they fail to accurately predict phenomena. Theories are robust and comprehensive explanations of phenomena supported by a wide array of evidence; they are not simply guesses. When a well-established theory or law is contradicted by new, high-quality, verifiable experiments, it can lead to modifications to the original theory or law, or even to its complete replacement.