So to explain that -- if you've got an elementary particle and you shine a light on it, then the photon of light has momentum, which knocks the particle, so you don't know where it was before you looked at it.
Pavyzdžiui, jeigu elementariąją dalelę apšviečiate, šviesos fotono impulsas numuša dalelę, taigi jūs nesužinote, kur ji buvo prieš jums ją stebint.