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The measurement problem in quantum mechanics is the unresolved problem of how (or if) wavefunction collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer. The wavefunction in quantum mechanics evolves deterministically according to the Schrödinger equation as a linear superposition of different states, but actual measurements always find the physical system in a definite state. Any future evolution is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the process under examination. Whatever that "something" may be does not appear to be explained by the basic theory.
In mid-2004, John Conway and Simon Kochen of Princeton University proved the Free-will Theorem. This theorem states "If there exist experimenters with (some) free will, then elementary particles also have (some) free will." In other words, if some experimenters are able to behave in a way that is not completely predetermined, then the behavior of elementary particles is also not a function of their prior history. This is a very strong "no hidden variable" theorem.
The Conway-Kochen proof of the Freewill Theorem relies on three axioms they call SPIN, TWIN and FIN:
SPIN
Particles have the 101-property. This means whenever you measure the squared spin of a spin-1 particle in any three mutually perpendicular directions, the measurements will be two 1s and a 0 in some order.
FIN
There is a finite upper bound to the speed at which information can be transmitted.
TWIN
If two particles together have a total angular momentum of 0, then if one particle has an angular momentum of s, the others must necessarily have an angular momentum of -s.
In other words, the spin of a particle is dependent solely on the direction from which it was measured and not on its history. But we have already seen from the Kochen-Specker paradox, there is no way for a particle to predetermine its spin in every direction in a way consistent with SPIN.
The wave-function is real but nonphysical: A view from counterfactual quantum cryptography
Counterfactual quantum cryptography, based on the idea of interaction-free measurement, allows Bob to securely transmit information to Alice without the physical transmission of a particle. From local causality, we argue that the fact of his communication entails the reality of the quantum wave packet she transmits to him. On the other hand, the travel was not physical, because were it, then a detection necessarily follows, which does not happen in the counterfactual communication. On this basis, we argue that the particle's wave function is real, but nonphysical. In the classical world, the reality and physicality of objects coincide, whereas for quantum phenomena, the former is strictly weaker. Since classical cryptography is insecure, the security of quantum counterfactual cryptography implies the nonphysical reality of the wave function.
originally posted by: neoholographic
QM shows that conscious choice does something to the wave function.
originally posted by: neoholographic
This makes sense because matter doesn't have any observable properties prior to measurement so where do these observables come from? Where do these observables exist? I submit they exist in the non physical consciousness of the wave function.
This is not true. The wave function, when it decoheres, collapses into what is loosely described as "a choice". This doesn't mean that anything is physically chosen by anything conscious, its just a term used for lack of a better explanation and for lack of understanding. You don't choose which slit the particle goes through. The particle doesn't choose (as far as we know). All we know is that there is a probability of 50/50 chance of where the particle will wind up.
Specifically, decoherence does not attempt to explain the measurement problem. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".
originally posted by: neoholographic
a reply to: smithjustinb
Thanks for the reply. You said:
This is not true. The wave function, when it decoheres, collapses into what is loosely described as "a choice". This doesn't mean that anything is physically chosen by anything conscious, its just a term used for lack of a better explanation and for lack of understanding. You don't choose which slit the particle goes through. The particle doesn't choose (as far as we know). All we know is that there is a probability of 50/50 chance of where the particle will wind up.
This is a current misconception of decoherence. Decoherence has nothing to do with the choice of the observer and it doesn't try to explain the measurement problem.
originally posted by: neoholographic
a reply to: smithjustinb
When people try to use decoherence to support something like many worlds interpretation, they're simply trying to ignore consciousness by saying there isn't any measurement problem.
Decoherence does not generate actual wave function collapse. It only provides an explanation for the observation of wave function collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wavefunction are decoupled from a coherent system, and acquire phases from their immediate surroundings. A total superposition of the global or universal wavefunction still exists (and remains coherent at the global level), but its ultimate fate remains an interpretational issue. Specifically, decoherence does not attempt to explain the measurement problem. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".
originally posted by: neoholographic
a reply to: smithjustinb
Choice isn't irrelevant in QM. If I don't choose to carry our a measurement then how is which path information going to be known?
Choice isn't irrelevant in QM. If I don't choose to carry our a measurement then how is which path information going to be known?
So, you don't have to choose to measure anything. If there exists the ability for the information to be known, the wave will decohere. In a lab setting, yes, I guess you probably have to choose to set up the detectors and set up the experiment, but the actual choosing to do that has little to do with how decoherence occurs. Decoherence can happen independent of choice and independent of observation. Its not that you choose to observe. Its that the path is able to be known. If any evidence gets left behind for any event that occurred, it means that the event took place in a defined state. So, decoherence can happen independent of a conscious observer.