because atheists don't say we "know 100% there is no god",
even if one did- that would be a simple statement of opinion based upon the lack of evidence. the only thing that would be able to tell is if that person would change thier opinion if valid scientific evidence was presented that proved god's existance.
when atheists say "there is no god"- it is easier than typing and/or explaining the following:
there is no evidence to support the idea of god, further, the odds of gods existance, are so improbably remote that it might as well be considered impossible. however, since there is no conclusive proof that there is no god, one cannot logically say there is no chance,
but to prevent you confusing this "almost impossibly remote chance" with a reasonable "chance"- the odds of god's existance are much less likely than spiderman really existing, wonderwoman really existing and the two of them have a "love child" who is born as a sentient robot who can transform into a truck called "optimus prime".
isn't saying "there is no god" easier?
and scientists don't "change" any theory on a daily basis, in order for something to become a theory in the first place it requires rigorous testing and observation by MANY scientists.
scientists change thier minds based upon this testing and observation and collaboration with others and thier results, but that would generally occur before something becomes a theory- once a hypothesis has been tested to the point it can become an accepted theory- then it would be much harder to "disprove" that theory since you would need to explain why those earlier testing yeilded those results as well.
you need to gain a basic knowledge of science and scientific theory before posting something like this again.