"We have to remember that what we observe is not nature itself, but nature exposed to our methods of questioning."
- Heinsenberg
Heisenberg's 'Uncertainty Principle' of 1925 postulated that the act of measuring something changes the thing you are measuring, so you can never be sure of the measurement you made (simply stated).
Concerned with the dynamics of electrons to neutrons in an atomic particle, he found...
The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa.
--Heisenberg, uncertainty paper, 1927
While he was applying his principle to sub-atomic particles, the same 'uncertainty' can be said of nearly all observations.
The more you try to get into it's 'workings', the more uncertain will be your measurements of a system.
In the area of opinion polling, for example, simply asking questions, however finely crafted, brings issues into the mind of the person being surveyed that affects how they will respond to the question. Had you not asked the question, the respondent might have followed a totally different path than the one they answered.
An excellent site about Heisenberg and his work is at:
http://www.aip.org/history/heisenberg/p08.htm
Chidester, GA
