"[In] scientific thinking ...we can only be completely confident about relatively simple statements. For example, it may be a fact that there are three trees in your backyard. However, our knowledge of how all trees are related to one another is not a fact; it is a complex body of knowledge based on many different lines of evidence and reasoning that may change as new evidence is discovered and as old evidence is interpreted in new ways. Though our knowledge of tree relationships is not a fact, it is broadly applicable, useful in many situations, and synthesizes many individual facts into a broader framework. Science values facts but recognizes that many forms of knowledge are more powerful than simple facts.” (UC Berkeley link above)
And then, if they ask you whether you believe in it, you can tell them that while a theory is well supported by multiple lines of evidence, putting absolute faith in a scientific theory is not scientific. No one can fault you for refusing to commit your final opinion, because science does not have the final word. And that’s a fact.