Speakable and unspeakable in quantum mechanics by J.S. Bell

Much of research on quantum entanglement originated from J.S. Bell’s work. This book is a collection of Bell’s papers. I followed the advice of Bell on the order of reading. I have browsed paper 18, 20, 16, 3, and 17. I probably won’t have time to read any further in the near future.

The following are some quotes and comments on the papers, as well as quotes and comments on the introduction of 2022 Nobel Prize in Physics.

On the impossible pilot wave

Why did such serious people take so seriously axioms which now seem so arbitrary? (p 166)

Comment: This applies to Arrow Debreu model and Debreu’s approach in general.

Six possible worlds of quantum mechanics

Thus in contemporary quantum theory it seems that the world must be divided into a wavy 'quantum system', and a remainder which is in some sense 'classical'. The division is made one way or another, in a particular application, according to the degree of accuracy and complete[1]ness aimed at. For me it is the indispensibility, and above all the shiftiness, of such a division that is the big surprise of quantum mechanics. It introduces an essential ambiguity into fundamental physical theory, if only at a level of accuracy and completeness beyond any required in practice. It is the toleration of such an ambiguity, not merely provisionally but permanently, and at the most fundamental level, that is the real break with the classical ideal. (p 188)

2022 Nobel Prize in Physics

Remarkably, quantum teleportation is the only way to transfer quantum information from one system to another without losing any part of it. It is absolutely impossible to measure all the properties of a quantum system and then send the information to a recipient who wants to reconstruct the system. This is because a quantum system can contain several versions of every property simultaneously, where each version has a certain probability of appearing during a measurement. As soon as the measurement is conducted, only one version remains, namely the one that was read by the measuring instrument. The others have disappeared and it is impossible to ever know anything about them. However, entirely unknown quantum properties can be transferred using quantum teleportation and appear intact in another particle, but at the price of them being destroyed in the original particle. (p 3)

 “This is because a quantum system can contain several versions of every property simultaneously, where each version has a certain probability of appearing during a measurement. As soon as the measurement is conducted, only one version remains, namely the one that was read by the measuring instrument.” 

Comment: How to extract information in all versions? You can only find out one version in measurement. Measurement collapsed all other versions.

“However, entirely unknown quantum properties can be transferred using quantum teleportation and appear intact in another particle, but at the price of them being destroyed in the original particle.” 

Comment: If the original information is destroyed, how do you know you get a faithful copy?