• The text in italics is copied from that url
• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
Quantum indeterminacy can be quantitatively characterized by a probability distribution on the set of outcomes of measurements of an observable.
That means it is human related, it defines our human limitations and does not say anything directly about the physical state of what we want to measure i.e. the 'universe'
The distribution is uniquely determined by the system state, and moreover quantum mechanics provides a recipe for calculating this probability distribution.
Quantum Mechanics can only define a model of what happens at particle level.
In quantum mechanics, however, indeterminacy is of a much more fundamental nature, having nothing to do with errors or disturbance.
From a phylosophical point of view indeterminacy (i.e the uncertainty principle) has nothing to do with errors or disturbance.

### 2 Indeterminacy and incompleteness

This failure of the classical view was one of the conclusions of the EPR thought experiment in which two remotely located observers, now commonly referred to as Alice and Bob, perform independent measurements of spin on a pair of electrons, prepared at a source in a special state called a spin singlet state.
The spin singlet state is defined as 2 particles. One particle has spin up and the other has spin down.
The question is how can you perform a thought experiment with those two particles?
It was a conclusion of EPR, using the formal apparatus of quantum theory, that once Alice measured spin in the x direction, Bob's measurement in the x direction was determined with certainty, whereas immediately before Alice's measurement Bob's outcome was only statistically determined.
To get a spin singlet state you have to perform first an experiment which creates those two particles. Next you have to measure the spin of each particle to establish that from one particle the spin is up and from the other down.
Next you have to perform the same experiment 1000 times including the measurements to establish that this particular experiment in 99.8% of the cases creates the spin singlet state.
The next time when you perform the same experiment and you measure the spin state of one particle. If the state is up than you know for sure that the state of the other particle is down.
This knowhow is purely established by experiment and does not need any theory or thought experiment.
From this it follows that either value of spin in the x direction is not an element of reality or that the effect of Alice's measurement has infinite speed of propagation.
The only speed that is involved is the speed of the two particles. In some cases they are in opposite directions.
There exists no issue around the concept: "The speed of propagation of Alice measurement". The measurement of Alice i.e. any disturbance of the particle that Alice wants to measure has no physical influence on the second particle.

### 4 Logical independence and quantum randomness

In classical physics, experiments of chance, such as coin-tossing and dice-throwing, are deterministic, in the sense that, perfect knowledge of the initial conditions would render outcomes perfectly predictable.
No it does not. Perfect knowledge does not exist. It does not exist at elementary particle level. That is why there exist no clear boundary between a classical system and a quantum system. The problem lies in the detail.
The ‘randomness’ stems from ignorance of physical information in the initial toss or throw.
When you use a roulette the final outcome of any throw is caused by lack of information. That is why it is impossible to repeat any experiment.
In diametrical contrast, in the case of quantum physics, the theorems of Kochen and Specker, the inequalities of John Bell, and experimental evidence of Alain Aspect, all indicate that quantum randomness does not stem from any such physical information.
In the case of experiments with involve elementary particles there also exist lack of information. In that sense both are the same.

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Created: 12 December 2017

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