Saturday 26 November 2016

quantum mechanics - Particle interactions which are NOT considered observations?


When considering the term "observe" often used in discussions related to quantum entanglement and the collapse of a wave functions, I found text I quote at the bottom of this question (I've also linked to the source).


My question: What is an example of an interaction between particles (or waves) that DOES NOT constitute an "observation" of certain (or any) of the particle (or wave's) characteristics? Apologies in advance if this question is entirely misguided or invalid.



An "observation" does not require an actual mind to perceive it. Rather, a particle/wave is "observed" as having certain characteristics whenever it interacts with any other particle/wave in a way that would require it to have those characteristics. As in Eogan's example. if a particle/wave is involved in a collision, then its wavefunction must "collapse" into a subset that is compatible with it having been at that particular time and place and having the particular energy and vector required for the collision. In short, particles observe each other wherever and whenever they interact. It is actually quite difficult to get any large number of particles to interact without collapsing.




http://forums.xkcd.com/viewtopic.php?f=7&t=75527#p2789781



Answer



All observations imply interactions, any measurement is the result of an interaction.


Do all interactions imply observation? It is a matter of how one defines "observe". In the above quote the verb is used as synonymous with "interacting", and the answer will be by construction "none".


If observe means a specific experimental setup to measure something, then in general,in parallel with the sought for interaction , for example Higgs production, a number of other interactions are taking place which are not "observed" in the setup, for example production of a Psi going undetected because the experiment is not set up to detect it/observe it.


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