Quote:
Originally Posted by pagan3142 
The Heisenberg uncertainty principle or just Uncertainty principle states that one cannot measure values (with arbitrary precision) of certain quantities, which are pairs of observables of a single elementary particle. These pairs include the position and momentum. It is often confused with the observer effect.
In science, the observer effect refers to changes that the act of observing has on the phenomenon being observed. For example: observing an electron will change its path because the observing light or radiation contains enough energy to disturb it. In quantum mechanics, if the outcome of an event has not been observed, it exists in a state of superposition, which is being in all possible states at once. The most famous example is the thought experiment Schrödinger's cat, in which the cat is neither alive nor dead until observed — until that time, the cat is both alive and dead (technically half-alive and half-dead in probability terms). |
Well let's start with Heisenberg and then go on to Copenhagen (the observer effect). Both are features of wave-particle duality and relatively(!) easily resolved.
Heisenberg says that you can't measure the position and the momentum of a particle at the same time; the more accurate the one, the less accurate the other. This relates to the duality of matter which moves as a wave which collapses to form the particle only (and only) when it interacts with another waveform such that they exceed a critical probability. When the waveforms do collapse we have two particles which interact (as illustrated in Feynman diagrams) following which they are reabsorbed and continue their (new) paths as waveforms. As the motion only relates to the waveform, you can measure the velocity/momentum but not the position. As the position relates only to the particle (after the waveform has collapsed) you can measure this accurately but not the velocity/momentum.
'Copenhagen' is the principle that an observer is necessary for the collapse of the wave function - otherwise the outcome is undecided and hence my interest in the subject. This begs a very simple point - it is not the
observer that causes the collapse of the waveform - it is the
observation and only the observation, regardless of whether anyone is there to witness the result. The act of creating an observation requires a detector and this needs a reaction between (at least) two particles which is what causes the collapse of the waveform. Thus the collapse of the waveform is just the same as any other particle interaction in nature, the only difference being that it was done for the purpose of obsevation/experiment. [I've just discovered (thanks to Drifter) that this is called the "objective collapse theory".]
The dual slit experiment involves the same principles. These issues are now discussed in more detail, with illustration, in my own TOE - The Dance of Shiva
Felix