....If we take the question of certainty in a philosophical discourse, YOU HAVE A POINT. In science, however, we do not claim absolute certainty...only degrees of certainty and probabilities and approximations. You may be tempted to think you've got me there. But let me just give you an analogy of what scientists are doing in trying to understand nature. It goes like this:
Imagine that the gods are playing a cosmic game of chess. You are a tiny observer who doesn't know the rules of the game, but you're allowed to look at the board from time to time and from a little corner.
Through observations, you try to figure out the rules of the game and the rules that the pieces follow. You might discover, after a while, that a piece seems to be moving along the same color. You call this a BISHOP and then noted this consistent behavior. But later on, you discover another theory for the bishop, that it moves on a diagonal. And this refines the theory that you've understood before, that it maintains its color. This process is analogous to how scientists first discover one theory and then later find a deeper understanding of it as new evidence comes along.
Let's say everything's going well and we're discovering one theory after another. All of a sudden, some strange phenomenon occurs. So you begin to investigate it. IT'S CASTLING, something you didn't expect. And that adds to your understanding of what the king can do, under certain rules and circumstances.
Occasionally, we could have a revolution in science. We may be very comfortable and secure in our theory about the bishops...that no two bishops would move along the same color on the board. And then, one day, we discover that it is no longer the case. We see an instance of two bishops moving along the same color. How could this be? Only later do you discover a new possibility: that the bishop actually got captured and then a pawn went all the way to the other end to produce a new bishop. That could happen but you didn't know it.
JUST A SHORT DIGRESSION. Actually, speaking about "scared of being disproven", scientists are always trying to investigate those things in which they don't understand the conclusions. It's the thing that doesn't fit that's the most interesting, the part that doesn't go according to what you expect.
And so, it's very analogous to the way scientific theories are. They sometimes look very secure, they keep on working, and all of a sudden, some little gimmick shows that they don't seem right anymore. And then we have to investigate the conditions under which this deviation happened, and so forth. And gradually, we refine the theory to explain the phenomenon more deeply, more precisely and more comprehensively.
Unlike the chess game though, where the rules become more complicated as you go along---in science, when you discover new things, the whole picture looks more simple. It looks complicated at first because we're learning from a new experience which does not fit into our current set of theories. But if you realized, every time we expand into the wilder regions of experience, every once in a while we have these UNIFICATION of theories, in which everything's explained together...and it turns out to be simpler than it looked before...when distinct phenomena used to have their own separate theories.
Examples of unification are the following. First, take heat and mechanics. When atoms are in motion, the more motion, the more heat the system contains. And then the theories of heat and all temperature effects got unified under the laws of mechanics. Another example is the discovery of the relation between electricity, magnetism, and light, which were found to be different aspects of the same thing--- what we call today the electromagnetic field. Another example is the unification of chemical phenomena, the various properties of various substances and the behavior of atomic particles, which is in the quantum mechanics of chemistry.
The question is, of course: IS IT GOING TO BE POSSIBLE TO UNIFY EVERYTHING? Nobody knows. All we know is that, as we go along, we find that we can amalgamate pieces, and then we find some pieces that do not fit, and we keep trying to put the jigsaw puzzle together. Whether there are finite number of pieces or whether there is even a border to the puzzle, is of course UNKNOWN. It will never be known until we finish the picture, IF EVER.