explain why the results of one experiment are never really final answers?

Answer 1

Experiments are used to test theories. Theories are general statements that encompass an large class of observations. It would generally require an infinite number of experiments to test every conceivable prediction of a theory, so you can never definitively prove a theory is valid in all cases. The best you can do test a finite set of representative cases and call it good.

For example, the theory of General Relativity makes the prediction that any starlight the passes close to the sun's surface is slightly deflected by a certain amount. You can test the prediction during a few representative eclipses, but a necessary (but insufficient) condition to prove it beyond *all* doubt would require you to test it for every star in the sky. Get it?

Answer 2

I can think of one example, in quantum physics ...

Heisenbergs Uncertainty Principle says you cannot know everything about a particle. You may know its mass, or velocity or direction, etc. But, you cannot know ALL the facets of information - the universe forbids it.

I'm not sure if this is what you meant - I don't think you can say that EVERY experiemnt is indecisive (think or the Michelson Morley experiment - it involved extremely precise measurements over a period of months - for a single experiment, yet it was successful; winning them a Nobel pprize for the effort and interpretation).

Or are you meaning that you need multiple experiments to 'smooth out' small errors you accidently introduce?