I What is an observable exactly?

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What is an observable exactly? I hear terms that are used in physics books like an observable or a detection. What types of equipment do physicists use to make all these quantum measurements that are used in books so frequently? How small of a region of space does the wave function "collapse" into when measuring particles?
 
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dsaun777 said:
How small of a region of space does the wave function "collapse" into when measuring particles?
Whether wave function collapse happens at all is an open question (different interpretations of quantum mechanics say different things on this topic).
 
dsaun777 said:
What types of equipment do physicists use to make all these quantum measurements that are used in books so frequently?
One example of equipment is photodetectors. But there are other types of equipment used, depending on what is studied. Examples of additional equipment: magnets, polarizers, waveplates etc.
 
Technically, an observable is just a Hermitian operator on whatever Hilbert space you're working in.
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and Education IBM) stated... Source: https://www.physicsforums.com/insights/quantum-entanglement-is-a-kinematic-fact-not-a-dynamical-effect/ by @RUTA
If we release an electron around a positively charged sphere, the initial state of electron is a linear combination of Hydrogen-like states. According to quantum mechanics, evolution of time would not change this initial state because the potential is time independent. However, classically we expect the electron to collide with the sphere. So, it seems that the quantum and classics predict different behaviours!
According to recent podcast between Jacob Barandes and Sean Carroll, Barandes claims that putting a sensitive qubit near one of the slits of a double slit interference experiment is sufficient to break the interference pattern. Here are his words from the official transcript: Is that true? Caveats I see: The qubit is a quantum object, so if the particle was in a superposition of up and down, the qubit can be in a superposition too. Measuring the qubit in an orthogonal direction might...

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