Hey, I’m a theoretical physicist and would love to hear abt the new QM theorem!
Oh Hell yea!
Quantum mechanics is quite a different field when compared to classical physics - many things, especially related to measurements of properties, work very differently from the way we are used to seeing the world. Like, if you go to the doctor and get your height and weight measured, the order shouldn't matter. In a quantum setting, one of these measurements might change the outcome of the other.
As a physicist you (probably) know about the uncertainty principle. This states that you cannot measure both position and momentum with infinite precision. Rather, the more precise you measure one of them, the less precise you will know the other. Therefore, you always have a bit of uncertainty spread out over the two properties. In fact, there are lots of properties that cannot be measured simultaneously this way!
The theorem I did my thesis on adds one more layer on top of this. We know that it is sometimes impossible to precisely measure two things at the same time, but can we always measure one variable?
It turns out that the answer is no. Sometimes, if you have one single property of a system that you would like to measure, it still has an uncertainty relationship. Not to a different variable, but to the very laws of nature! The WAY-theorem is a result from 1960 that tells us that a bounded observable (= thing that can be measured) cannot be precisely measured if it interacts with the laws of nature in a certain way.
However, not all observables are bounded. One example of an unbounded observable is energy: if you have an object with a certain amount of it, you can theoretically always find or crate a state with more. The mathematical techniques used in the 1960 paper could not be generalised to this unbounded case, though.
That is why two researchers published a new version of the theorem in 2024, using modern mathematical techniques to prove it. My own work was about rewriting this proof in a more understandable way. With this result in place, we have a more complete understanding of quantum measurements, and especially their limitations!
