Heisenberg's uncertainty principle refers to what is believed to be a fundamental limit to the precision allowed in certain measurements. For example, the more precisely the position of an electron is determined the greater the uncertainty in a measurement of its momentum (and vice versa). This is sometimes explained in terms of how detection of the electron will require interaction with a photon – an interaction which will modify the state of the electron. (Although this is so, the uncertainly is thought to be fundamental feature of nature – not just something revealed in making measurements.)
Although the effect is only significant in measures at a very fine scale, the idea is often transferred to notions of social research along the lines that the any kind of measurement will change what is being measured.
