Title: Observer effect - Simple English Wikipedia, the free encyclopedia
Headings: Observer effect
Observer effect
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Use in science
Use in Information technology
Use in the social sciences
Observer bias
References

Content: Likewise, a standard mercury-in-glass thermometer must absorb some thermal energy to record a temperature, and therefore changes the temperature of the body which it is measuring. A common lay misunderstanding of the term refers to quantum mechanics, where, if the outcome of an event has not been observed, it exists in a state of ' superposition ', which is something like being in all possible states at once. In the famous thought experiment known as Schrödinger's cat, the cat is empirically neither alive nor dead until observed – until that time, the cat is theoretically both alive and dead (technically half-alive and half-dead in probability terms). However, most quantum physicists, in resolving Schrödinger's seeming paradox, now understand that the acts of 'observation' and 'measurement' must also be defined in quantum terms before the question makes sense. From this point of view, there is no 'observer effect', only one vastly entangled quantum system. A significant minority still find the equations point to an observer; John Archibald Wheeler, who probably worked more deeply on this subject than any physicist thus far, devised a graphic in which the universe was represented by a "U" with an eye on one end, turned around and viewing itself, to describe his understanding. The Heisenberg uncertainty principle is also frequently, confused with the "observer effect". The uncertainty principle actually describes how precisely we may measure the position and momentum of a particle at the same time – if we increase the precision in measuring one quantity, we are forced to lose precision in measuring the other. Thus, the uncertainty principle deals with measurement, and not observation.