Essential randomness of quantum measurement and philosophical problems raised by that.
Every object or system of objects in the universe is described by a wavefunction, a mathematical function that has some value at every point in space. It doesn’t matter what you’re describing—an electron, a dog treat, a cat in a box—it has a wavefunction, and that wave-function has some value no matter where you look.
Schrodinger Equation governs the behaviour of wave functions.
A quantum object can only be observed in one of a limited number of allowed states.
The wavefunction of an object determines the probability of being found in each of the allowed states. By creating different scenarios for a case, you’ll have a wavefunction and it’ll lead you to that probability.
Measuring the state of an object absolutely determines the state of that object.
Superposition is having the probability of existing in two different positions (double slit experiment)
Polarization of Light allows us to filter light and absorbe at some point in an experiment setup. It’s like marking the photons so we will know what happen at that step of the experiment, thus the measurement principle is changed. When we measure the polarization using a filter, we will find the photon in one of those two states (either passing through the vertical filter, or being absorbed by it), and not anywhere in between.
Polarized photons thus provide an excellent system for looking at the core principles of quantum mechanics. Each individual photon can be described in terms of a wavefunction, with two parts corresponding to the two allowed states, horizontal and vertical polarization. That wavefunction gives you the probability of the photon passing through a polarizing filter, and after you make a measurement of the polarization with a filter, the photons are in only one of the allowed states. A single photon passing through a polarizing filter demonstrates all the essential features of quantum physics. As a result, polarized photons have been used in many experiments demonstrating quantum phenomena.
Double slit experiment creates an interference pattern which indicates the superposition state. When we block one slit, we know where that photon is going to end up but we don’t know when we have two slits.
Each individual photon is random but when we repeat the experiment, we end up with the interference pattern.
Tries to avoid the problems of superposition and measurement by drawing a strict line between microscopic and macroscopic physics.
Werner Heisenberg insisted quite strongly that it was a mistake to talk about electrons having an independent reality. In his view, the only things we can really talk about are the outcomes of specific measurements. He rejected the whole notion of talking about what the electrons were doing between measurements.
Also seems to be saying that physical reality does not exist until a measurement is made, which poses its own philosophical problems: Scrodinger’s Cat and Wigner’s Friend
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