What does the act of observing do exactly?

[lox_and_whiskey]

Quite the opposite - 'knowing of quarks' explains nothing of the observed behaviours i referenced above. QM would be the worst example one can find for describing observed reality in ALL fields of science. Period.

If you mean observed like "with your eyes" then this is like saying that a lawn mower can't chop down an oak tree. It's true, but that's not what it's made for. You can derive any other statement from QM, but what you're saying is that it's a lot of work, and there is usually already a body of work readily available. The field of optics can tell you how to manipulate light on the macro scale. You could derive all of optics from QM, but why do the work when you could just buy an optics textbook?

 

[stevendaryl]

Its simply an interaction that leads to decoherence.

Is it that simple? I was thinking about the whole business of quantum measurement, and it seems to me that there are (or can be) two distinct interactions involved in a measurement (I'm not sure if you consider an observation and a measurement to be the same thing, or at least the same sort of thing):

1. Amplification, whereby a microscopic property of the system to be measured triggers a macroscopic change in the measuring device.
2. Decoherence, whereby the measuring device interacts with the environment (or with other parts of itself) so as to destroy interference between alternative measurement results.

It's doesn't seem to me that decoherence has to be involved in the measurement interaction itself. Instead, decoherence just insures that a macroscopic object always seems to have a definite macroscopic state (that is, no interference between macroscopically distinguishable alternatives). I guess you could eliminate the measurement device, and just allow the system to directly interact with the environment, leading to decoherence, but in that case, I'm not sure whether you would say that anything has been "observed" or "measured" (unless you just redefine observation to mean loss of coherence, I guess).

 

[naima]

The word observation is very misleading in QM. It suggests an observer. There is only interactions.
Who was the first guilty of its use?

 

[stevendaryl]

The word observation is very misleading in QM. It suggests an observer. There is only interactions.
Who was the first guilty of its use?

Every observation is an interaction, but not every interaction is an observation. To me, the distinction is that an observation is an interaction that leaves a persistent record (whether a dot on a photographic plate, or a memory of the brain of a scientist, it doesn't matter).

 

[vanhees71]

Well, all of physics is about observing something in nature. I don't know, who was "guilty" to invent physics. I'm also not so sure that inventing physics was such a major sin of mankind either ;-).

 

[naima]

There is science when you can verify formulas. It seems that it will be easier to get a formula for Stevendaryl type of interaction than to your scientist worker!

 

[Zafa Pi]

There are a number of parameters that we don't know how to determine, from first principles:

1. The charge of the electron.
2. The mass of the electron.
3. The mass of a hydrogen nucleus.
4. The mass of an oxygen nucleus.

But I think that quantum mechanics can in principle determine all the other properties of water from these parameters. In practice, I'm not sure how much is actually doable.

Has anyone shown how to find the density in principle? Why do you think it's possible?

 

[Gerinski]

Isn't an experiment resulting in an interference pattern at the screen an "observation" or "measurement"? You all seem to concentrate on the outcomes which result in "collapse of the wavefunction" as the only definition of observation or measurement or "persistent interaction" or whatever you may want to call it. Many observations do not collapse the wavefunction and simply result in interferences.

Interference is simply the outcome of an observation which does not contain precise information about the preceding state because it is consistent with more than one. Whenever we (or nature) don't demand the interaction to produce a persistent definite piece of information which could influence the future, the outcome will be an interference, i.e., a superposition of all the possible outcomes each of them with their respective probabilities.

An interference pattern is as valid a result of an observation as a single dot. The difference lies in the information contents of each kind of observation outcome.

 

[naima]

In the Young interference pattern you have a precise result wih a persistent mark about the distance between the slits and the energy of the particles. interferometers are measurement devices.

 

[Gerinski]

Yes that's what I was meaning.