<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> In physics, the observer effect is the theory that simply observing a situation or phenomenon necessarily changes that phenomenon . This 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 . Similarly, it is not possible to see any object without light hitting the object, and causing it to reflect that light . While the effects of observation are oftentimes negligible, the object still experiences a change . This effect can be found in many domains of physics, but can usually be reduced to insignificance by using different instruments or observation techniques . </P> <P> An especially unusual version of the observer effect occurs in quantum mechanics, as best demonstrated by the double - slit experiment . Physicists have found that even passive observation of quantum phenomena (by changing the test apparatus and passively' ruling out' all but one possibility), can actually change the measured result . A particularly famous example is the 1998 Weizmann experiment . The "observer" in this experiment--a sophisticated electronic detector--wasn't human . And yet, possibly because the word "observer" implies a person, such findings have led to a popular belief that a conscious mind can directly affect reality . The need for the "observer" to be conscious has been rejected by mainstream science as a misconception rooted in a poor understanding of the quantum wave function ψ and the quantum measurement process . </P> <P> For an electron to become detectable, a photon must first interact with it, and this interaction will inevitably change the path of that electron . It is also possible for other, less direct means of measurement to affect the electron . It is necessary to distinguish clearly between the measured value of a quantity and the value resulting from the measurement process . In particular, a measurement of momentum is non-repeatable in short intervals of time . A formula (one - dimensional for simplicity) relating involved quantities, due to Niels Bohr (1928) is given by </P>

Quantum physics tells us that nothing that is observed is unaffected by the observer