Introduction to Physics

By Santosh Chaudhary, M.Sc (Physics) Nalanda Open University Observer In physics, an " observer " refers to any device or entity that records an event in a way that touches so many other atoms and particles, such as by radiation or vibrations, that reversing the event becomes statistically nearly impossible.  An observer in physics is any entity that makes a measurement of a physical system. This can be a human being, a scientific instrument, or even another physical system.  In classical physics , the observer is typically assumed to be passive, meaning that their presence does not affect the system being observed. This is a good approximation for many macroscopic systems, but it breaks down at the microscopic level. Here are some  examples of the observer effect in physics: When you measure the voltage of a battery, you are drawing a small current from the battery, which changes its voltage slightly. When you weigh yourself on a scale, the scale is compressing your bo...