For your convenience, here is the error:
David Byrden
Karma: 6
This paper is wrong.
The error is simple. The overall quantum system is also simple, but obfuscated by the authors spelling out all the steps of the setup.
As some have pointed out here, it’s not a system that we could practically implement with people in “labs”, no more than we could implement Schrodinger’s Cat. But we can implement this system using quantum equipment. In fact Hardy’s Paradox refers to a mathematically equivalent system which has been built (and works just as QM predicts).
So it behooves us to identify the error in the author’s reasoning. It is this;
At the very beginning of the setup, they have “agent /F” read a quantum “coin”. This entangles her with the “coin” and puts her into a superposition of “tails /F” and “heads /F”.
The agent “tails /F” then calculates the results of the experiment AS IF SHE WAS THE ONLY COPY OF HERSELF. She ignores the contribution of her twin, “heads /F”. But from the point of view of an outside observer, they both contribute information to the qubit that they jointly emit.
The entire chain of reasoning in the paper is based on this faulty assumption and is therefore wrong.
The Renner-Frauchiger paper has been refuted, but usually with a lot of math. So I tried to write the simplest possible explanation, here:
http://byrden.com/quantum/Renner-explained.html