Blog of Veikko M.O.T. Nyfors, Hybrid Quantum ICT consultant

Quantum Mechanics demystified, a try

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Superposition and it’s collapse

Superposition is the kind of normal state for any quantum object. In superposition state, quantum object is a bunch of energy, with all of it’s properties wiggling wildly. In this state, we are not able to determine the exact state of the object in an understandable or measurable way for us humans. Properties like spin, momentum, location or any other of the quantum properties are kind of in between in linear combination of all the possible values. This linear combination of values is characterized by a wavefunction like Schrödinger equation:

\[i\hbar \frac{\delta }{\delta t}|\psi(t)\rangle = \hat{H}|\psi(t)\rangle\]

When an interaction with some other object then takes place, superposition ceases to exist and energy is given to the other party. We say the superposition or wavefunction gets collapsed. At this stage quantum properties will get materialized according to the probabilities of related wavefunction.

Like a photon of blue light traveling all the way from sun to earth, it is in superposition most of the travel. When it reaches upper atmoshere, it interacts with some molecule there, loosing it’s superposition. It gets scattered as we say. And we see the blue sky. Blue by the way, instead of e.g. red, for the reason that blue photons with their shorter wavelength interact more easily with molecules up there.
Nobody is there to make an observation of any kind. Photon only bounces into another blue photon being in superposition. This may happen over and over again. Eventually a descendant blue photon hits our cone or rod cell, superposition collapses, creating an electric signal into optic nerve. This time the collapse of superposition was observed.

When the collapse takes place, the other party doesn’t have to be anything that would make it visible for humans. Like the atoms in upper atmosphere. If the target of interaction happens to be something, that leaves a trace for us humans to be seen, then we are pretty near to the case, where people keep on saying observation collapsed the wavefunction. But that’s not what happened. See Measurement problem explained