The Dionysian

Am I correct in saying that the reason they speak of observers affecting things in quantum physics is because the observer has to use tools to observe such things? It's not some mystical mind/matter thing as so many like to think right?

Philosoft

As I understand, the fundamental nature of observation is not well-understood. There are naked-eye observations that collapse wave functions, like the double-slit experiment and Scrodinger's Cat, however. Heisenberg said it's impossible to know both the energy level and position of a particle, maybe that's what you're thinking of.

beausoleil

False dichotomy. Neither of the above, although it is sometimes explained as a version of the former.

Rusting Car Bumper

It fundamentally comes from that fact that the things that one detects when observing a system are actually representations of a change in state in the system.

For example, if a particle, an electron, is in a state and you "see" it, then this means the electron has given off a photon (a "light particle"). However, because the electron has given off a photon then this means its lost energy and thus its state has changed. (You can in fact, throw photons at electrons in order to "see" them with the same consequence.) Hence the observational mechanism is actually a thing that causes a state change. Thus, observation causes state change.

That is a basic example in a nutshell. However, one needs to remember that this effect is not really important on macroscopic levels.

DC

[edited to clear up pronouns.]

[ December 10, 2002: Message edited by: DigitalChicken ]</p>

Shadowy Man

I agree with beausoleil.

I read a good book on the subject called Where does the Weirdness Go.

Rain Dog

In order to detect something you have to let it to interact with your measuring apparatus in some way. Without the interaction, there is nothing to detect. Indeed, what you’re detecting is a change in the measuring apparatus. This change is unavoidably accompanied by a change in the thing being measured. What makes things interesting is the fact that the vast majority of states available to a thing don’t actually have definite values for the sorts of things we might want to measure, like position, and momentum, and energy and so on. This is at the heart of the weirdness of quantum mechanics, that things don’t actually have these properties as definite values. In order to measure one of these properties, that the thing doesn’t actually have, we have to impose upon it a state that is in some sense closer to one in which it does have the property that we want to measure. The more precise we want the measurement to be, the more we have to impose on the thing and drive it toward a state that has a definite value of the property we want to measure. The Uncertainty Principle notes that states that are close to having definite position are far from states that have definite momentum, and vice versa, so that by measuring one of these properties, we disrupt the thing in a way that decreases the extent to which it has the other.

-RD