According to the Heisenberg uncertainty principle, there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be simultaneously known. This means that the more precisely you try to measure one of these properties, the less precisely you can know the other.
In the context of the uncertainty principle, it's important to understand that it applies to the behavior of particles at the quantum level. It does not mean that particles are physically located in multiple places simultaneously, but rather that their properties, such as position and momentum, cannot be precisely determined simultaneously.
When you observe a particle, you effectively interact with it and obtain information about one or more of its properties. The act of measurement or observation collapses the wavefunction, which is a mathematical description of the particle's quantum state, into a specific outcome. As a result, the particle's properties become well-defined within the constraints of the uncertainty principle.
For example, if you measure a particle's position very precisely, its momentum becomes highly uncertain. Similarly, if you measure its momentum with great precision, its position becomes highly uncertain. This does not mean the particle is physically spread out or exists in multiple places at once, but rather that there are inherent limitations in the simultaneous knowledge of these properties.
In everyday macroscopic objects, the effects of quantum uncertainty are negligible and not observable. The uncertainty principle becomes significant at the microscopic scale, where the quantum behavior dominates.