In short, the states of the Heisenberg uncertainty principle that it is impossible to know both the exact position and exact speed of an object at the same time. However, the effect is tiny and only visible to the subatomic scale.
Werner Heisenberg (1901-1976) was a German physicist who helped formulate quantum mechanics in the early 20. He first presented the Heisenberg uncertainty principle in February 1927 in a letter to Wolfgang Pauli, then published the same year.
Light can be considered as composed of packets of energy called photons. To measure the position and velocity of any particle, the first thing that shed light on it, then detect the reflection. On a macroscopic scale, the effect of photons on an object is negligible. Unfortunately, subatomic scales, the photons that hit the subatomic particle will move significantly, so although the situation has been accurately measured the speed of the particle is altered.
By knowing the position, which has provided all the information you had on the speed useless. In other words, the observer affects the observed.