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nouveau_riche
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what is the difference between observation and measurement in reference to quantum mechanics?
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments.
...all measurements have an associated operator (called an observable operator, or just an observable)...
Ken G said:I'd have to agree that there is no established scientific difference between an observation and a measurement, other than the implication that a measurement is quantitative and an observation can be more informal (I "observe" that the Moon is full tonight, etc.). One might argue that one has to do an observation following every measurement to see how the measurement came out, but again the distinctions seem scientifically unimportant. Whether or not either of those needs to be carried out by a conscious individual is a question of subjective philosophical priorities. For example, we can maintain that only conscious beings do observations, or we can maintain that an observation occurs whenever we could imagine a conscious being on the scene without affecting the outcome in any scientifically relevant way (but still need the concept of conscious beings), or we can maintain that conscious beings have nothing to do with measurements, and in a universe devoid of any life, one rock can still be twice the size of another one. I can't really see the latter as a coherent perspective personally (rocks have no idea what "size" even means), but I see nothing in science that adjudicates these possibilities, and indeed that is a good thing, because it allows us all to agree on scientific results even though we don't agree on these philosophical priorities.[/QUOTE?]
i think it's about the difference between quality and quantity,but in reference to quantum mechanics when will the wave function collapse occur,on observation or measurement?
Demystifier said:Observation requires a conscious observer, measurement doesn't.
If we adopt the lexicon that a measurement is a quantification and an observation is a perception (which is a kind of qualia but can refer to a quantity, like the qualia of a quantity), then which one "collapses" the wave function depends on our interpretation of QM. In the "consciousness collapse" picture, which essentially places the collapse at the "last possible moment" but seems too mystical to many physicists (I have no idea why, I think they may have lost track of their own mysticisms), then we would hold that the observation causes the collapse, not the measurement. Or for those who favor interpretations in which collapse is a physical dynamical phenomenon like any other (so independent of our consciousness), the measurement causes the collapse (in the sense that a measurement involves coupling with macroscopic systems, regardless of whether or not any of them include a brain). Then of course we have orthogonal views like Bohm and MWI-- in Bohm, the system starts out collapsed, so what we perceive as collapse is simply when we get the message, and in MWI, it starts out uncollapsed and never collapses, our perceptions are a kind of pervasive illusion. (To which I would argue that when an illusion is pervasive enough, we don't call it an illusion any more.)nouveau_riche said:i think it's about the difference between quality and quantity,but in reference to quantum mechanics when will the wave function collapse occur,on observation or measurement?
Ken G said:If we adopt the lexicon that a measurement is a quantification and an observation is a perception (which is a kind of qualia but can refer to a quantity, like the qualia of a quantity), then which one "collapses" the wave function depends on our interpretation of QM. In the "consciousness collapse" picture, which essentially places the collapse at the "last possible moment" but seems too mystical to many physicists (I have no idea why, I think they may have lost track of their own mysticisms), then we would hold that the observation causes the collapse, not the measurement. Or for those who favor interpretations in which collapse is a physical dynamical phenomenon like any other (so independent of our consciousness), the measurement causes the collapse (in the sense that a measurement involves coupling with macroscopic systems, regardless of whether or not any of them include a brain). Then of course we have orthogonal views like Bohm and MWI-- in Bohm, the system starts out collapsed, so what we perceive as collapse is simply when we get the message, and in MWI, it starts out uncollapsed and never collapses, our perceptions are a kind of pervasive illusion.
Which of these is the "real truth"? Well, shouldn't we know by now that none of them are, but they each give us a way of thinking about what is happening?
I'm not sure what you are asking, it sounds like you are mixing the cases where the outcomes are treated as discrete vs. continuous. The above issues appear in either situation, and either type of probability amplitude can oscillate, but they are different situations that should not be confused.nouveau_riche said:if collapse occur by observation , how could Schrodinger equation give solution with oscillating probability amplitudes? shouldn't it be just peaks at every point observed(collapse)
Ken G said:I'm not sure what you are asking, it sounds like you are asking a probability to know what the outcome will be before it happens, but that's not what probabilities are.
Ah, you are asking about how we connect the Schroedinger equation to the observations. That's pretty much what all the hullaballoo is about with the various interpretations, right there. It's the main bugbear of quantum mechanics! I won't go into all the interpretations, each one is pretty much a thread of its own, so I'll just say how the theory itself handles it-- via the "Born rule", which converts the wavefunction (from the Schroedinger equation) to the probability of some given outcome (the "collapse"). This means, your answer is not in the Schroedinger equation itself, it is in what we do with the output from the Schroedinger equation. If this seems somewhat ad hoc to you, you are not alone-- many physicists have worked very hard to improve the situation with a more general set of postulates that makes the Born rule seem to follow more naturally, but none have achieved widespread acceptance, so the current state of the art is to simply plug in the Born rule and not worry where it comes from. (The Born rule says that the probability of a given measured outcome is the squared magnitude of the associated coordinate of the wavefunction when expanded on the eigenbasis of that measurement operator.)nouveau_riche said:what i mean to say is that observation is causing collapses,how could it be that a wave function is evolving as given by Schrodinger equation under non collapsible condition when the only way to see that evolution is to observe it
Observation is the act of using our senses to gather information about the world around us, while measurement is the process of quantifying that information using numerical values.
Both observation and measurement can be reliable, but it ultimately depends on the context and the accuracy of the tools used. Observations can be subjective and prone to bias, while measurements are more objective and precise.
Yes, observation and measurement often go hand in hand in the scientific method. Observations can help guide the design of measurements, and measurements can validate or refute observations.
Observation in science can include using our senses to observe the behavior of animals, the growth of plants, or the properties of substances. Measurement in science can include using tools such as rulers, thermometers, or spectrometers to quantify the length, temperature, or composition of objects.
Observation and measurement are essential for gathering data and evidence to support or reject hypotheses in science. They allow us to make accurate and objective observations about the natural world, leading to a deeper understanding of how it works.