From: goldenfieldquaternions@gmail.com   
      
   On Saturday, October 13, 2018 at 10:56:46 AM UTC-5, Nicolaas Vroom wrote:   
   > An article with this title is in Nature of 28 September 2018 at page 446.   
   > The first sentence of this article reads:   
   > "New twist on thought experiment yields conflicting results"   
   > The subject of the article is a new version of the Erwin Schr=C3=B6dinger's   
   cat   
   > thought experiment in which the cat is replaced by two human beings   
   > (Alice and Bob) and with two observers. (one for Alice and one for Bob)   
   >   
   > My problem with this thought experiment is how can you claim, based on the   
   > outcome of this thought experiment, anything about the real world.   
   >   
   > The article contains the following sentence:   
   > "One of the two friends (Alice) can toss a coin and - using her knowledge   
   > of quantum physics - prepare a quantum message to send to the other friend   
   > (Bob). Using his knowledge of quantum theory, Bob can detect Alice's message   
   > and guess the result of her coin toss"   
   >   
   > For me this text is not clear, is not complete and does not give enough   
   > detail. What means: "her/his knowledge of quantum physics"?   
   > What is a "quantum message"? How does Bob "guess"?   
   >   
   > What baffles me the most is the answer on the question:   
   > What have human observations to do with the physical state of any process.   
   > Specific what have human observations to do with the half-life of a radio   
   > active process? IMO nothing. IMO it is much better to replace   
   > the cat with a counter and count the number of gamma particles released.   
   > Ofcourse you can claim that before you look at the counter, the counter   
   > is in a set of states simultaneous (like both dead and alive) but   
   > that is of no physical significance.   
   >   
   > Nicolaas Vroom   
      
   This argument may be against counterfactual interpretations of   
   quantum mechanics. The argument of Frauchiger and Renner depends   
   upon whether a third observer makes a measurement to verify that   
   Alice and Bob agree.  If there are counterfactual definiteness in   
   the quantum world this argument hold, in that the third observer   
   can find that Alice and Bob do not agree, and this holds even if   
   the third observer makes no measurement. Counterfactual definiteness   
   means there would have been a type of outcome had a particular   
   measurement been made. Quantum interpretations that permit   
   counterfactual definiteness are the deBroglie-Bohm interpretation,   
   the Stochastic interpretation of Nelson, similar to deBrogle-Bohm,   
   and the Transactional Interpretation of Cramer.  I am sure there   
   may be others. Quantum interpretations have in recent years multiplied   
   like bunnies.   
      
   If we reject counterfactual definiteness the result of Frauchiger   
   and Renner is then not consistent or false in such a system or   
   interpretation. The truth of Frauchiger and Renner conclusion depends   
   upon counterfactual definiteness. We might then see this result as   
   less about quantum mechanics as it is with interpretations of QM.   
   Remember that QM is a completely deterministic physics in that a   
   wave function is unitary evolved. However, this describes the   
   evolution of amplitudes that define probabilities for outcomes in   
   a measurements. These outcomes are completely stochastic, and their   
   occurrence is with an actual detection or measurement. This is where   
   we get into nettlesome issues of wave function collapse, many worlds   
   and the rest.   
      
   Raamsdonk illustrates how spacetime might be built up from large N   
   entanglements of states. This large N might run into the problem   
   that Frauchiger and Renner illustrate. The occurrence of a classical   
   spacetime that is resistant to quantization, except at the most   
   extreme Planck energy, means there is some firmness to the idea   
   that classical reality is separate from quantum physics. The reality   
   of a quantum wave or state is slippery.   
      
   I am rather agnostic about the result of Frauchiger and Renner; I   
   am not sure whether this has some impact on nature. We do have this   
   conundrum with the dichotomy between quantum and classical physics,   
   where Bohr saw this as a necessary feature of his Copenhagen   
   Interpretation. However, we also have a sense that any classical   
   object is ultimately built up from quantum particles, waves or   
   fields. In some ways nature performs an einselection, to use Zurek's   
   term, the quantum bases that pertain to the classical world. Some   
   might argue it is not nature that does this, but rather minds or   
   the action of a mental being coming aware of of quantum outcomes.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)