text: This non-Doppler effect phenomenon creates the Lorentzian profile of spectral lines because it causes natural broadening.
full_question: This non-Doppler effect phenomenon creates the Lorentzian profile of spectral lines because it causes natural broadening. This statement is responsible for the nonzero value of zero-point energy. One of these statements exists for any set of variables that do not commute, such as for time and energy. The formulator of this statement created a thought experiment involving a microscope attempting to observe an electron.  This statement sets a lower bound of the reduced Planck's constant over two. For 10 points, name this principle which states that the position and momentum of a particle cannot both be precisely known. 
first_sentence: This non-Doppler effect phenomenon creates the Lorentzian profile of spectral lines because it causes natural broadening.
raw_answer: Heisenberg uncertainty principle