In absolute sense: NO. In the practical sense: YES. We design machines that can go to Mars and send back images with the science we have. But will the "Theory of Gravity" predict correctly the results of every experiment that it applies to? Who knows? We will never run every experiment so there is always going to be room to doubt any theory.
OTOH, have you seen any rocks falling up lately? Me neither so Newton had a pretty good theory despite the fact that it wasn't "true".
Actually I think I got that backwards but you get the idea.