Why cannot you know? When you say you cannot know, you give up on the concept of rational, scientifically explainable Universe. That's not acceptable and it's dangerously close to a religion.
In a way I just think the entire question is silly and pointless because you don't know whether you will ever know one way or the other. And knowing the answer might not even really be relevant.
I mean on the one hand, there are things in life you can be sure of to such a degree that questioning them is not only pointless, but a little strange. For instance I am 99.9999% certain that there is a coffee cup next to my computer screen.
There are other things where even how you ask the question is extremely difficult if not impossible. How can I even begin to fathom the idea of something that is everywhere, all the time, controlling or not controlling everything in dimensions of existence that I can't even perceive, or that I may not even be aware of? Even if I wanted to know this thing existed, or that it didn't exist, I wouldn't know what questions to ask or how to find the answers. If the answer was given I might not even realize that is the answer.
To me, believing that you "know" the answer one way or another involves making an assumption. Now assuming things isn't always bad, for instance although I cannot see my cat right now I am assuming he is still alive, as any other assumption would not be very productive or rational based on the information I currently have. I know nothing other than when I left my house this morning, I fed the cat, and the cat was alive and healthy, and my house was not in any immediate danger of being destroyed. Ergo assuming my cat is still alive, even though I am not totally certain he is alive, is the rational thing to do.
In a personal matter such as this there are a variety of reasons to make the necessary assumptions to come to the necessary conclusions, some of which are eminently reasonable, some of which are downright foolish. But, one must make an assumption regardless. For whatever personal reasons some choose to make that choice regarding the existence of God or some higher power, some do not. For my own personal reasons, most of which would probably bore you and everyone else to death, I have decided to make the choice to not make the choice, because I think making the choice doesn't matter.