Projection Postulate vs Quantum Randomness

[LarryS]

The Wikipedia article Quantum Indeterminacy discusses the measurement problem and possible reasons why measurement values are inherently random.

In the section labeled "Measurement", the Projection Postulate is briefly discussed. After explaining the Projection Postulate, in the second paragraph of that section, the author makes the statement "It is immediate from this that measurement in general will be non-deterministic.". To me, that conclusion is not obvious at all. Comments?

Thanks in advance.

 

[mattt]

What is deterministic or stochastic is a mathematical model. Non Relativistic Quantum Mechanics admits a Deterministic Model, for instance, Bohmian Mechanics (it has to postulate some unobservable elements, kind of non-local hidden variable, to achieve its goals).

Also in Many-Worlds (or Many-Branches) Model of QM, the evolution of the Universe (all the branches) is unitary (deterministic), non "essential" randomness (though it must reproduce the Born rule under concrete circumstances, in every decoupled branch).

In short, what we have (all we really have) is different mathematical structures (more or less successful/useful) and experimental data.

A totally deterministic mathematical model and a stochastic mathematical model can sometimes both explain equally well a given set of experimental data.

 

[bhobba]

It an unanswerable question, at least at this stage of our knowledge of physics.

Take Bohmian Mechanics - its totally deterministic but you can't know the initial conditions due to the uncertainty principle to predict anything so you must use probabilities. Its the same with Many Worlds - it too is deterministic but doesn't predict which universe you as a rational agent will experience - it could be any of the possible outcomes - so one can only give likelihoods.

It is also possible QM is the limit of a deeper theory that is deterministic and all we experience here in the macro world it simply something similar to statistical mechanics.

It also maybe nature is simply like that - fundamentally probabilistic.

We need some kind of experiment to decide but nobody has ever figured out one - and indeed its possible nature is such its fundamentally impossible to ever have such an experiment.

Thanks