Final answer:
Scientific theories gain credibility from successfully predicting previously unknown phenomena, with experimental verification serving as a key indicator of their validity. The ability to predict and experimentally confirm phenomena, such as electromagnetic waves and antimatter, underscores the strength of theoretical physics.
Step-by-step explanation:
The statement that theories which successfully predict previously unknown phenomena are more credible than those that do not is essentially a cornerstone of scientific methodology. The success of a theory in predicting phenomena that have yet to be observed is a powerful demonstration of its validity. For example, predictions such as the existence of electromagnetic waves and antimatter were confirmed through experimentation, underscoring the predictive power of theoretical physics. On the other hand, a theory that fails to predict new phenomena, or whose predictions are contradicted by experiments, must be adjusted or abandoned, reflecting the scientific principle that empirical evidence is critical for the establishment and validation of scientific theories.
General theories must be in harmony with existing data and current theories. When a theory's predictions are experimentally verified, it reinforces the unity and connectivity of physics as well as highlights the remarkable capability of science to uncover the order of the universe. Thus, the predictive success of theories contributes significantly to their credibility within the scientific community.