Observation

Observation - Is to perceive without active participation. Observation has been paramount to the development of science.

Suppose a particle has momemtum p and a position x. In a Quantum Mechanical world, I would not be able to measure p and x precisely. There is an uncertainty associated with each measurement, e.g., there is some dp and dx, which I can never get rid of even in a perfect experiment!!!. This is due to the fact that whenever I make a measurement, I must disturb the system. (In order for me to know something is there, I must bump into it.) The size of the uncertainties are not independent, they are related by
dp x dx > h / (2 x pi) = Planck's constant / ( 2 x pi )

So in a 'Quantum Mechanical world' , absolute reality cannot be 'observed' entirely accurately.