Just as our ability to express or conceive of the the Divine is. Theoretical concepts must be tailored to the realities of life -- let's face it, we are limited in everything we do, know or say -- and I would say, believe.
Once advance physics are contemplated on a post graduate level, people do disagree
Because it becomes more intellectual and not readily verifiable; you go from a working model to a theoretical construct, informed speculation, an educated "guess."
Besides, I am talking not of belief in gravity but belief in the scientific method
That's apples and oranges. People recognized that things fall on earth. One does not need scientific method to come to that conclusion. To this day we have no clue why gravity exists. It is an "invisible force" that is made evident by falling objects, water flowing downhill, etc. We know that it is related to mass and that it is an integral "property" of mass.
We don't need Scripture to believe in God. Our belief without them may be somewhat "deficient" but we recognize that we live in a physical world, a universe. We recognize that nothing in it is the way we would have built or designed. We recognize that it is "limitless" from our perspective and we recognize that (1) either nature existed eternally or (2) something that existed before nature did, probably eternally, created it. This is not theology (or religious scientific method) but simple facts which we all believe because we see them. As they say, "seeing is believing."
I guarantee you that it would be easier to claim Christian teaching if there was a preponderance of historical and other kind of evidence of the story of both Testaments.
What we do know is that +Ignatius was ordained bishop by +Paul, and +Polycarp by +John. They were real people because we have evidence of their existence. Therefore, the two Apostles in question existed, and since the teachings of the aforementioned bishops agreed with those, and used the teachings of, the Apostles as true -- first hand -- we have every reason to believe that their faith was the same faith we proclaim today.
Where certitude begins to break down is when we start making claims such as "multitudes" following Christ and no one making a single note of it. There is no historical evidence of the massacre Herod allegedly ordered in order to kill baby Jesus. Surely, someone like Josephus would have mentioned something about it -- after all, Josephus went into extraordinary detail of Herod's life. But there is no mention of anywhere (which doesn't mean it didn't happen, only that we have not found it yet).
Believing in God and in gravity are two distinct and incomparable processes. As for the scientific process, a belief in it is never absolute.
The faith in scientific method is the faith that because things have fallen on earth they will continue to fall on earth. It is so ingrained in you that you don't see it for what it is, a belief.