Quotes: Do not put faith in traditions, even though they have been accepted for long generations and in many countries. Do not believe a thing because many repeat it. Do not accept a thing on the authority of one or another of the Sages of old, nor on the ground that a statement is found in the books. Never believe anything because probability is in its favor. Do not believe in that which you yourselves have imagined, thinking that a god has inspired it. Believe nothing merely on the authority of your teachers or of the priests. After examination, believe that which you have tested for yourselves and found reasonable, which is in conformity with your well-being and that of others. — Siddhartha Gautama [The Buddha] (c. 563-483 bc) Nepali-Indian Spiritual Teacher
A theory is a model of the universe, or a restricted part of it, and a set of rules that relate quantities in the model to observations that we make.
A theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations.
Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with the theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory.
The ideas about scientific theories assume that we are rational beings who are free to observe the universe as we want and to draw logical deductions from what we see. Yet if there really is a complete unified theory, it would also presumably determine our actions. And so, the theory itself would determine the outcome of our search for it! And why should it determine that we come to the right conclusions from the evidence? — Stephen Hawking (1942-2018) A Brief History of Time