Quantum mechanics and the uncertainty principle

Question

I have a limited understanding of this so please forgive my question if it borders on the moronic. From what I can gather from what I've read from various books, the internet an popular culture etc. Quantum events are considered to be uncertain, the position or states of the very small objects under consideration are not definite but fall under the description of a waveform. Which is a spatial description that gives probabilities of locating the small at a given point in the surroundings. (well as far as I can make out). Shroedingers cats hypothetical experiment is used to give a picture of this to the audience. And as far is I can understand from it, the cat is said to be in two states, alive and dead simultaneously until the experimenter opens the box and observes the situation. At this event the uncertainty collapses and the fate of the cat is revealed. What I understand from this is the macroscopic event of opening the box forces "causally" the quantum events to come to a conclusion and there is no more uncertainty. The waveform collapses and the state of the quantum event is revealed at that time, and as is the cats fate.

So my question is, does the HUP mean quantum events have no definite state until you measure them or observe them? Or do quantum events have a definite state at a particular point in time but this state is simply unknown to us until we observe them? Or are we supposed to draw something else from the picture of quantum mechanics? And the thing that bugs me is isn't everything unknown and uncertain to an experimenter or observer untill they observe or measure it anyway? So the waveform description is unnecessary and things are simply unknown, or is the waveform a description of an observers perception of the unknown? I am a bit confused and any direction would be appreciated. Thanks for being patient if i have not grasped the concepts correctly, but I find the topic puzzling.

Answer 1

The current quantum theory says that everything has a quantum state, which defines its wavefunction (the most basic concept of "state" you'll see in QM). However, quantum states are not measurable in a classical sense. There is no known way to fully capture a quantum state using classical measurements.

The most famous example, position and momentum, proves to be a useful example. You and I, thinking classically, think of position and momentum separately -- as independent concepts. In quantum mechanics, these two concepts are entwined into a position-momentum state. We can never truly know what this position-momentum state is, but we can choose to measure position, or measure momentum. However, if we try to measure both, we find that there's an uncertainty in it which cannot be reduced, built right into the equations and definitions which describe what it means to measure a state.

As for your last paragraph, there are several interpretations of QM. QM is just a set of equations. It is the interpretation which provides some physical meaning for those equations. You are most familiar with the Copenhagen interpretation. It's the most popular (for historical reasons), but there are several others. Many Worlds Interpretation will give you a different interpretation of what these things "mean" to us. deBroglie-Bohem Pilot Wave will give a different interpretation. All of them us the same QM equations, but they interpret them different ways in an attempt to "bring them to life" in a way which jives with classical physics.