Undergrad What does the act of observing do exactly?

[Jilang]

The act of observing proves we are here. Would then the anthropic principle then set some tight tolerances on the charge of the electron in natural units?

 

[marcophys]

What does the act of observing do exactly?
Some interesting philosophical replies in this thread, however, my guess is that you were looking for a rational explanation.
Here is how an engineer would view it (pompously speaking on behalf of engineers, so please forgive me):

Using 'two slits' as the ideal
We have a light sensor attached to a computer - a 'gate open' records, a 'gate closed' we don't record.

We passively observe the results of impact.

The impact has occurred... our observation changes nothing because the impact has already happened.​

We passively observe the projectile, on course, prior to impact.

If this was a large solid object, it would be reflecting light.
We would be observing reflected light - not the object.
Therefore, this would be no different to observing the results of impact.
Ie. No change​

Even an extremely small solid object reflects, or blocks light.
Whether the gate is open or closed... no change occurs.​

We now examine the passage of a photon.

Does it block light, or reflect light?
If another photon hits it... does it change course?

The question is:
Can we observe the photon by observing it's interaction with it's immediate environment?

Let us say we can observe the consequences of interaction.
Other photons are disturbed, and these enter the sensor.
In effect, these are physical results that indicate the passage of the monitored photon.
Whether the gate is open or closed, has no bearing on the photon.
The photon is doing what it is doing, regardless of our recording of the event.

As long as we change nothing, we record the physical event.
The photons random nature is irrelevant to us.
We observed 'it'.
Whether the gate was open or closed... the photon was there.​

The problems occur when we cannot monitor interaction.

Let's say that we must apply a force, which the photon passage must alter.
The force must impact upon the photon.
But... if the force is ever present... the photon must do what it will do, in the presence of this force.
This, regardless of whether our distant gate is open or closed.
Therefore, we still record reality, only that it is a reality modified by our applied force.​

The concept that 'the position of the photon would change according to whether the gate is open or closed' is purely theoretical.

We will have recorded the physical reality.

That is the engineer's view ( er nice ) of observation.

 

[bhobba]

numerous discussions about the significance of this disappearance occur, maintaining that there is something misterious in it (Copenhagen interpretation).

Things have moved on a lot since the early pioneers musings.

Decoherence has illuminated things. The issue now is why do we get any outcomes at all or technically how an improper mixed state becomes a proper one. The formalism is silent on it. My ignorance ensemble interpretation simply assumes it does. Other interpretations have their own take eg in BM its trivial because particles have real properties at all times.

The modern version of Copenhagen is consistent/decoherent histories where QM is the stochastic theory of histories. Interestingly its often described as many worlds without the many worlds.

Thanks
Bill

 

[bhobba]

What does the act of observing do exactly?

Its simply an interaction that leads to decoherence.

Thanks
Bill

 

[lox_and_whiskey]

My question is simple though I fear the answer may be complex: What does the act of observing do exactly? I hear observing does some unexpected things in quantum (I wouldn't doubt there is a religon based on it).

I am a math major with a love of physics though I'm not that versed in it so please do pile on the formulas if you wish but be nice with the physics. Thanks for responding in advance,

-Ben Orin

Well, it is said that the act of observing something will alter it. Basically, my impression is that, in order to get information about what's happening, there must be interaction, and interaction alters the inputs. This is not a specifically quantum mechanical idea, but it does become important there.

For example, while it may seem that macro-scale objects are not being altered as we observe them, every photon striking the surface is altering the object, and the object is altering the photons. The frequency of the light changes i.e. the color changes, and when said photons enter a person's eye they can see the different colors of all the objects around them.

It's just that a photon being so tiny relative to an average macro-scale object, the changes are not significant to that object. This is great on the macro-scale, but in quantum mechanics one is obviously concerned with the behavior of the very small, and there's nothing smaller to observe it with. An average hardcover book, for example, could be said to be about 10^17 larger than a particular photon. But if you want to observe a photon, there's nothing out there 10^17 smaller than a photon.

 

[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.