Science makes an attempt to approximate truth based on observation, experiment, and the data at hand. Science is very careful about calling anything as truth without absolute and undeniable proof... that's why they have so many Scientific Theories and very few Scientific Laws.
Actually, there is a small but important detail about the words "theory" and "law" in science.
When Newton proposed his models he used the word "law" because he thought he really had found an immutable fact about nature. Now scientists know that there are no hypothesis that will certainly withstand the test of time intact, so they call the best hypothesis available "theories", not "laws".
So, for example, Evolution is a theory which might get some updates in the unforeseeable future, but no scientist is really expecting it to be totally reversed, ever. It is as close to total truth as you can find in science.
Theory is the highest level of knowledge in science. the phrase "it is just a theory" is only used by the ignorant who want to discredit science but have no argument.
Sometimes the word "law" is used for some theories because of historical reasons (like Ohm's law, or Snell's law) but real scientists know those are theories, and are as certain as anything can get in science.