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 ```There is a theory in science that "one cannot measure anything without effecting that which you measure". Who wrote theory is this?```
 ```Hi alan123, this sentence is one of the basic points in Quantum Theory. The most popular example dealing with this sentence is "Schroedinger's Cat" paradox as described in this article ( http://www.emr.hibu.no/lars/eng/cat/ ) by Erwin Schroedinger, first published in "Die gegenwärtige Situation der Quantenmechanik" in the German publication Naturwissenschaften (1935). You can find a nice discussion (which is probably easier to read than Schroedinger's paper) about the paradox here ( http://www.newtonphysics.on.ca/HEISENBERG/Chapter2.html ) The actual theory behind your sentence was mostly developed by Werner Heisenberg and is called "The Uncertainty Principle" (sometimes also called "The Principle of Indeterminacy"). Heisenberg worked together with Bohr an together they created the Copenhagen Interpretation of Quantum Theory ( http://www.benbest.com/science/quantum.html ). I think these quotes from Heisenberg are in line with the sentence you provided: "The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa." --Heisenberg, uncertainty paper, 1927 "I believe that the existence of the classical "path" can be pregnantly formulated as follows: The "path" comes into existence only when we observe it." --Heisenberg, in uncertainty principle paper, 1927 Understanding Heisenberg's theories is not a trivial task, so I am going to supply a few links that might explain the points relevant to your question: Uncertainty Principle http://www.thebigview.com/spacetime/uncertainty.html The Uncertainty Principle http://www.mtnmath.com/whatth/node53.html for a more in-depth understanding, you might want to read about the Wave-Particle-Duality explained here ( http://www.hotquanta.com/wpd.html ) and about Quantum Entanglement and Causality ( http://fergusmurray.members.beeb.net/Causality.html ). I hope this was helpful! I would have liked to write a more in-depth answer, however, this is such an exhaustive subject that books have been filled with it (if you need specific book recommodations, please ask for them!). Please feel free to ask for clarification should you require more information on any specific point! voyager-ga PS: One of the most famous quotes from the discussion about Quantum Theory was Einstein’s “God does not play dice.” (he was trying to disprove Quantum Theory with a number of thought experiments) Additional Resources: Heisenberg / Uncertainty Principle http://www.aip.org/history/heisenberg/ The Page of Uncertainty http://www.svsu.edu/~slaven/uncertainty/uncertainty1.html The Uncertainty Principle http://plato.stanford.edu/entries/qt-uncertainty/ Search Strategy: quantum entanglement ://www.google.com/search?hl=de&lr=&ie=UTF-8&q=quantum+entanglement&spell=1 schrödinger's cat ://www.google.com/search?sourceid=navclient&q=schr%F6dinger%27s+cat wave particle duality ://www.google.com/search?sourceid=navclient&q=wave+particle+duality uncertainty principle paper heisenberg ://www.google.com/search?hl=de&lr=&ie=UTF-8&q=uncertainty+principle+paper+heisenberg&spell=1```