Well, see here is the interesting thing about infinity.
Whatever may be actually happening on a molecular level, between molecules, could be compared to us walking around in the street, bumping into each other, or not, and if we do bump into each other, maybe one of us will have a cold and sneeze on the other, and spray micro-organisms on them, and maybe one of us will bump into someone who is really related to us, but neither of us knows it, but if you looked at our DNA, maybe even our blood, you would see that, just like you would see the micro-organisms on the handkerchief of the bumper and the face of the bumpee a few yards away.
So what about all the particles that are down several levels inside those molecules, that we don't even have equipment to perceive yet?
There could be things going on there that even looking at interaction of molecules themselves will not reveal.
Absolutely everything we know about anything is based, as simpleplan reminds us, on perception. Specifically, the perceptive organs of one species on one planet, a species that as katie points out, is believed to be using only a small % of its capacity to begin with. (I heard 10, she heard 5, but let's not quibble).
In such a situation, the line between science and speculation is more like a big blurry stripe, So blurry and translucent that you have to look hard to see it, and even when you do, you can never be quite sure it is not just your imagination...