A theory is accepted as true because of confirmation by experimentation. For something to become a theory, there has to be scientific evidence, including experiments, that show it has been true thus far. However, it cannot become a law without much more extensive testing. Theories are not false all of the time, as almost any law of science we see began as a theory. Theories can be disproved, as they often times are. Theories are not absolute truths due to the fact many have been disproved.
