4 ms·

"Quantum Bayesianism, or QBism as Fuchs now calls it, solves many of quantum theory’s deepest mysteries. Take, for instance, the infamous “collapse of the wave

"Quantum Bayesianism, or QBism as Fuchs now calls it, solves many of quantum theory’s deepest mysteries. Take, for instance, the infamous “collapse of the wave function,” wherein the quantum system inexplicably transitions from multiple simultaneous states to a single actuality. According to QBism, the wave function’s “collapse” is simply the observer updating his or her beliefs after making a measurement." https://www.quantamagazine.org/quantum-bayesianism-explained-by-its-founder-20150604/ https://www.quantamagazine.org/quantum-bayesianism-explained...

analog31 7y ago
I'm not really sure this helps. There is still the puzzle about how the updating of beliefs at some indefinite time in the future causes the collapse of a wavefunction involving photons that have fled the scene at the speed of light, for instance. It usually takes some ridiculously hard experimentation to support a new theory about fundamental quantum phenomena.
kgwgk 7y ago
It's not that simple. When a measurement is done on a pure state (where the knowledge of the state is already as good as it gets) the observers are not just updating their beliefs, they are changing the system. On the other extreme, in some cases one may have measurements that improve our (imperfect) knowledge of the physical state without disturbing it. "Quantum measurement is nothing more, and nothing less, than a refinement and a readjustment of one’s initial state of belief. [...] Let us look at two limiting cases of efficient measurements. In the first, we imagine an observer whose initial belief structure ρ = |ψ⟩⟨ψ| is a maximally sharp state of belief. By this account, no measurement whatsoever can refine it. [...] The only state change that can come about from a measurement must be purely of the mental-readjustment sort: We learn nothing new; we just change what we can predict as a consequence of the side effects of our experimental intervention. That is to say, there is a sense in which the measurement is solely disturbance." https://www.perimeterinstitute.ca/personal/cfuchs/Oviedo.pdf https://www.perimeterinstitute.ca/personal/cfuchs/Oviedo.pdf
kgwgk 7y ago
> the infamous “collapse of the wave function,” wherein the quantum system inexplicably transitions from multiple simultaneous states to a single actuality. By the way, the "collapse of the wave function" describes as well the transition from one state to another state. I don't understand what do you mean by "multiple simultaneous states".

analog31 7y ago

I'm not really sure this helps. There is still the puzzle about how the updating of beliefs at some indefinite time in the future causes the collapse of a wavefunction involving photons that have fled the scene at the speed of light, for instance. It usually takes some ridiculously hard experimentation to support a new theory about fundamental quantum phenomena.

kgwgk 7y ago

It's not that simple. When a measurement is done on a pure state (where the knowledge of the state is already as good as it gets) the observers are not just updating their beliefs, they are changing the system. On the other extreme, in some cases one may have measurements that improve our (imperfect) knowledge of the physical state without disturbing it. "Quantum measurement is nothing more, and nothing less, than a refinement and a readjustment of one’s initial state of belief. [...] Let us look at two limiting cases of efficient measurements. In the first, we imagine an observer whose initial belief structure ρ = |ψ⟩⟨ψ| is a maximally sharp state of belief. By this account, no measurement whatsoever can refine it. [...] The only state change that can come about from a measurement must be purely of the mental-readjustment sort: We learn nothing new; we just change what we can predict as a consequence of the side effects of our experimental intervention. That is to say, there is a sense in which the measurement is solely disturbance." https://www.perimeterinstitute.ca/personal/cfuchs/Oviedo.pdf https://www.perimeterinstitute.ca/personal/cfuchs/Oviedo.pdf

kgwgk 7y ago

> the infamous “collapse of the wave function,” wherein the quantum system inexplicably transitions from multiple simultaneous states to a single actuality. By the way, the "collapse of the wave function" describes as well the transition from one state to another state. I don't understand what do you mean by "multiple simultaneous states".