Quote:
Originally Posted by JohnD
The two are discrete and different.
Quantum physics treats particles and their properties as the probability that they hold those quantities and positions. Define the actual value of one, and the probability that it holds the others spreads out and smears. THAT's the Heisenberg principle. Nothing to do with observation, it's in the theory.
On the other hand, observer effect is a crude, macrocosmic effect as described above, and is very real. It may also be present in softer sciences such as psychology and sociology, and in the design of clinical trials, but it has nothing to do with quantum physics.
The drop of water and the thermometer is only an anology, and as scuh cannot be compared too closely.
JOhn
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I respectfully disagree. Trivially, of course measuring water temperature and particle positition are different acts of observation. Observing the behavior of chimpanzees by walking around with them is also a different act of observation. Still, it's useful to have a general category, call it the Observer Effect, to describe this general problem that plagues all sciences--even the so-called "hard" ones.
To say that it's the case that a particle never really has both a definite position and a definite momentum is pure metaphysics. There is not even in principle a way to decide whether positions and momentums are really discrete or not. I think
that was Heisenberg's main point: the HUP was not intended as a description of what particles are
really like independent of observers.
Thus, particle physics is in worse shape than your so-called "soft" sciences--maybe we should reverse the appelations! At least a clever thermodynamisist has a hope of correcting for the observer effect and arrive at an accurate estimate of orignal temperature of the water drop. An ecologist can try to correct for observer effect by comparing results obtained with less intrusive methods. A clinical trial can at least try to correct for the observer effect by using double-blind techniques.
The poor particle physicist, on the other hand, must of necessity be forever ignorant of the true nature of his or her chosen subject matter.
ETA: actually there are some sciences, like astronomy, that rely entirely on passive observation, and are therefore not subject to the observer effect.