People would be a good example. When someone is told they are being observed, something that is often necessary when performing scientific experiments, their behavior changes. It is reflected in interviewing processes where interviewees tend to give answers they think interviewer wants to hear.
In the natural sciences, there is a similar effect but is often the result of instruments that, by necessity, alter the state of what they measure in some manner. A commonplace example is checking the pressure in an automobile tire; this is difficult to do without letting out some of the air, thus changing the pressure. Furthermore, it is not possible to see any object without light hitting the object and causing it to emit light; while this may seem negligible, the object still experiences a change. This effect can be observed in many domains of physics and can often be reduced to insignificance by using better instruments or observation techniques.
As subatomic particles cannot be visibly observed, instruments have to be used that inadvertently change the behavior of the system. This is known as the Heisenberg effect, named after German Noble-laureate physicist Werner Karl Heisenberg (1901-76) whose uncertainty principle states that (in particle physics experiments) the very act of observing alters the position of the particle being observed and makes it impossible (even in theory) to accurately predict its behavior.
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