No that would be rather stupid of me. I don't pretend to know what I really don't know. So, do I KNOW that only the physical universe exists? NO.
However, if you CLAIM to know that something OTHER than the physical universe exists... bring us your SCIENTIFIC evidence for it, or your claim is silly. I never pretend to know that gods aren't POSSIBLE... my gosh, everything that hasn't been proved is POSSIBLE...even your god. But don't pretend that you have scientific evidence that your god exists. Of course you don't. IF you did, bring it to the world.
The world awaits your science, my friend. Otherwise, you are simply deluding yourself.
We KNOW and can test that the physical world exists. Now, what about your god claims?
Where is your scientific evidence?
Remember that your incredulity isn't evidence for anything.
Surely you're not pretending to know that no evidence exists for the existence of God and veracity of the Bible? There has been a long history of evidential apologetics engaging this very issue. It's not the lack of, or according to you the absence of, evidence that's the problem. It's the willful rejection of the evidence given in the created order of that which exists and in the soul of man. Even Bertrand Russell, in an honest revelation, when asked how he would reply if he were to die and find himself facing God asking him why he refused to believe, said "not enough evidence." Having science as your ultimate authority so that only that which can be observed by the senses and attempting to impose your fallible man-centered standard as that which you admit cannot account for the non-physical realm is an absurd demand for you refuse to accept my ultimate authority (the Bible); a glaring double-standard. And by attempting to engage in a logical discussion you lose the debate because your worldview, having science as your ultimate standard of truth, cannot account for the non-physical, universally true Law's of logic which Christianity does account for. You are evidencing the truth of Christianity by borrowing the truth explainable by my worldview to refute my worldview. Irrationally inconsistent and so self-refuting.