Seriously? Is it that difficult to imagine living in the world with no scientific knowledge whatsoever?
Yes.
"Scientific knowledge" covers quite a lot more than most people think it does. Science is not limited to formal laboratory study. It is used casually and informally at every point of your life. I have been over this before.
How does the rest of the animal kingdom manage the feat?
They don't.
Animals draw conclusions from observations the same way we do.
If you mean to say that scientific understandings are the only satisfactory answer to epistemological questions, plainly that isn't so either.
I've yet to see a case in which it isn't.
When you say testing, I take it you mean some kind of scientific process?
No. I mean "this is the prediction it makes, is that prediction correct Y/N".
Science is literally the only one that reliably, consistently turns up "Y". When it doesn't, it is demonstrably due to a flaw in the experiment, not with science itself.
No other epistemology has ever managed that.
I disagree with the idea that materialism is equivalent to a scientific understanding of the world.
They aren't equivalent.
Science is the methodology. Materialism is the conclusion we inevitably reach.
In fact, the idealist would say that science "works" because that's the way we imagine things to be.
A leprechaunist would say that gravity "works" because invisible leprechauns move everything around in such a way that it appears exactly as if Newton's theories are true.
There is a difference between ideas being consistent with observed reality and being rational.
Idealism is technically possible. It is in no way rational.
in other words, why should I think the universe is understandable at all, by any human methodology?
Because it is demonstrably so.
Or, in a similar vein, could the scientific method capture anything other than the measurements and conclusions we can reach with it? Don't the experiments, in some very real sense, create the results? (For an example of this, I offer up the coastline of England problem.)
Afraid I can't look that up at the moment. But in answer to the general question, we have no rational reason to believe that anything science cannot study is real. By definition, there is no evidence of any such thing, because if evidence existed, it could be studied scientifically.
Yes, it is a bit of a Catch-22. But that's because science is, at its core, very simple. "I have a question. In order to find the answer, I will look at all the facts and draw a rational conclusion without making unwarranted leaps or assuming things not in evidence".
That's it. That's all there really is to it. "Don't assume; look at the facts". Everything else is just degrees of formality, from casually assuming that a door will open into the same room it always has to building electron microscopes to try and unlock more fiddly secrets.