Why does it take so long for a scientist to agree on a scientific law?

Answer 1

The theory must be tested time and time again before it is made a scientific law. And scientific theories and laws must be "falsifiable" -- which means that it must be the case that if certain phenomena exist then the theory or law is wrong. Finding and testing every possible case that would falsify a scientific law is a neverending process. Only after many, many attempts to falsify a theory have failed are scientists willing to accept it as likely true.

Answer 2

It depends on what you mean by "long."

Hypotheses become widely accepted as theories* (at least in the scientific community) when they pass rigorous, observational tests. A scientist might develop a hypothesis that makes very specific predictions on what would be observed under certain conditions. If, indeed, those predictions turn out to be correct no matter the who or the where of the testing, then the hypothesis becomes accepted. If the tests are ambiguous, or there are no tests that can be done, then the hypothesis remains (well) a hypothesis.

A general rule of thought is that extraordinary claims (for example, a hypothesis that challenges a long standing theory) require extraordinary evidence. General relativity, for example, challenged our basic understanding of gravity and space; and initial experiments that suggested it was true did not immediately convince all scientists. When more refined measurements showed that observations perfectly matched the predictions of GR, it was accepted.

Thus, major challenges to long-help ideas are, by design, difficult to win acceptance -- the standard is set pretty high. If this were not the case, then science would be like the People's Choice Awards -- whatever just happens to be "hot" at any one time would be the accepted theory of that time. Fortunately, science requires a little more rigor.

For Copernicus, he could offer no test of his hypothesis of a heliocentric solar system -- his entire argument was that calculations were so much simpler with his idea. Not until Galileo thought of a test (phases in Venus), actually did the test, and then published the results; was Copernicus' ideas viewed as something more than just a useful aid to calculation.

* I request that you NOT misunderstand the word "theory" the way people who hate science misuderstand (or at least PRETEND to do so) the word. In science, an unproven speculation is called a "hypothesis." A hypothesis that has passed rigorous observational tests is a "theory." It is NOT an unproven idea.