“Know” seems like a very strong word. It cannot be “know” as in the sense of some verifiable claim like whether the earth goes around the sun or the sun goes around the earth.
Frankly, even with scientific truth, it isn’t always so easy to know the answer.
It seems indisputable now – except for some people – that the earth goes around the sun, even though “He set the earth on its foundations; it can never be moved” (Ps 104:5). Yet it was not so trivial a thing when Aristarchus (3rd century BC) claimed that the sun was at the center; it was “proved” wrong by Plato (of all people). When Copernicus first proposed the idea, not everything instantly worked correctly either. For one thing, reconfiguring things to the sun-centered model did not improve the predictions immediately. Perhaps the most damning case against the idea was produced by Tycho Brahe, who pointed out that an argument based on parallax (with the measuring techniques of the time – 1 arch minute) would mean the stars were more than 1/1000 of a parsec away. In fact, the nearest star is more than 3 parsecs away. A fire on a mountain might be visible 10 km away, but those numbers would have seemed absurd to a mind of the middle ages. So, actually, it wasn’t the church that initially resisted and scoffed at the Copernican model, it was actually the scientists! … (though they were called at the time “natural philosophers”.)
Dark matter? it’s on maybe a better standing than God as far as irrefutable evidence, but it has its problems and it certainly has not been directly measured (as of the moment I’m written this at least).
I live in Japan, where the main religions are Buddhism and Shinto. Most people here don’t really believe that deeply, but traditions drive at least a Buddhist funeral and a Shinto birth/land ceremony, etc. Whereas the model of ultimate reality is very different from the Judeo-Christian view, my discussion with Buddhists tells me that they are striving for some of the same things. I sense that there is something that all religious people are searching for. I don’t know how it works out at the end of the age, but I would expect that God is just and maybe even we don’t have it all correct ourselves.
At the end of the day, I don’t think we can tell you more than the parochial preacher would say – you need to have faith. Who gives faith? Well, from God. Because it is faith, we don’t “know” the truth, but we have come to trust that there is enough truth in this that we can go on with it. We also see some wisdom in the ages. Survival of that wisdom through thousands of years means there is something in it that still has wisdom – despite its many apparent flaws. Perhaps we look to the ages because it is a rock. As the famous hymn says, Twas Grace hast brought me safe thus far, and Grace will lead me home.
– by Grace we proceed,