Quantum Mechanics – What Does the Heisenberg Uncertainty Principle Tell Us?

heisenberg-uncertainty-principlequantum mechanics

In quantum mechanics, one of the first results students (and random people with an interest in physics) are exposed to is the Heisenberg Incertainty Principle. Informally, this principle expresses the product of the uncertainties of certain pairs of properties must be greater than some fixed value. Essentially, the "knowabilities" of certain pairs of properties of a quantum particle are linked such that certainty in one gives rise to uncertainty in another. Typically, the properties position and momentum are given as an example, so I will use those for the remainder of this question.

I will use $x$ and $\Delta x$ for position and uncertainty in position and $p$ and $\Delta p$ for momentum and uncertainty in momentum, all respectively.

My question is this:

If I make a measurement, and say I know the measurement has uncertainty $\Delta x$, what distribution should I expect "actual" position to follow. I know $\Delta x$ and let's say I know $\Delta p$ as well. These are numbers, they don't describe a physical state without some context. Are $\Delta x$ and $\Delta p$ the bounds of a uniform distribution describing the possible values of $x$ and $p$? Are they the variance of a normal distribution? Are they the variance (or some other property) of a distribution whose shape is determined by the quantum state of the particles interacting during the observation?

I have found some resources (like this one https://opentextbc.ca/universityphysicsv3openstax/chapter/the-heisenberg-uncertainty-principle/) that reference this but don't ever give an explicit answer. I also know that the Heisenberg Uncertainty Principle is a special case of the Cauchy-Schwarz inequality, which I plan to explore as an avenue to answering this question for myself.

Best Answer

Are they the variance of a distribution whose shape is determined by the quantum state of the particles interacting during the observation?

Yes.

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