Relational Quantum Mechanics Interpretation

[Smacal1072]

In Young's double slit experiment, any act of observation to determine which slit the particle passes through destroys the interference pattern.

Whenever I asked my physics professors why this was, their response was always either "Your question is physically meaningless", or, "There is no generally accepted explanation why this happens, only how it happens".

Like many other physics students, this disturbed me a little. I realize that QM is basically a "Shut up and Calculate" theory, but just so I could sleep at night, I adopted the http://en.wikipedia.org/wiki/Relational_quantum_mechanics interpretation:

Relational quantum mechanics (RQM) is an interpretation of quantum mechanics which treats the state of a quantum system as being observer-dependent, that is, the state is the relation between the observer and the system. - Wikipedia

This made more sense to me - It does away with the confusing wave-function collapse, and includes the observer as just another part of the quantum system under investigation. Also, systems that may appear to have "collapsed" to an eigenstate to one observer might still appear to be in a coherent superposition of states to another observer. In this way every system is a quantum mechanical system.

What do you all think about this? As far as QM interpretations go, it seems pretty reasonable to me...

 

[Demystifier]

Another old unanswered thread suggested by PF that may still be of interest to many readers here, even if the OP is no longer active.

Also, systems that may appear to have "collapsed" to an eigenstate to one observer might still appear to be in a coherent superposition of states to another observer.

Recent work on Frauchiger-Renner paradox has demonstrated that this, in fact, is inconsistent. I'm not sure, however, what are the implications on the relational interpretation.

 

[Marek Domanski]

In Young's double slit experiment, any act of observation to determine which slit the particle passes through destroys the interference pattern.

Whenever I asked my physics professors why this was, their response was always either "Your question is physically meaningless", or, "There is no generally accepted explanation why this happens, only how it happens".

Like many other physics students, this disturbed me a little. I realize that QM is basically a "Shut up and Calculate" theory, but just so I could sleep at night, I adopted the http://en.wikipedia.org/wiki/Relational_quantum_mechanics interpretation:This made more sense to me - It does away with the confusing wave-function collapse, and includes the observer as just another part of the quantum system under investigation. Also, systems that may appear to have "collapsed" to an eigenstate to one observer might still appear to be in a coherent superposition of states to another observer. In this way every system is a quantum mechanical system.

What do you all think about this? As far as QM interpretations go, it seems pretty reasonable to me...

 

[Marek Domanski]

To me the Schrödinger's cat experiment is a red herring, unless you believe that there has to be a conscious observer. The geiger counter would collapse the wave function
If you include the observer and an observer of the observer, then you get into an infinite regress and introduce QM into the macro-world. How would you evaluate the psi function in the macro-world? Also indeterminacy would then have to be part of our every day world. It would have to include quantum improbability. This is definitely not how we experience the world.

 

[gentzen]

To me the Schrödinger's cat experiment is a red herring,

... well, I would say that you are not totally wrong ...
According to Jan Faye in the SEP article on the Copenhagen Interpretation, even Bohr does not disagree with that conclusion: “Thus, Schrödinger’s Cat did not pose any riddle to Bohr. The cat would be dead or alive long before we open the box to find out.” However, I doubt that Bohr really said this, or replied to the content of Schrödinger’s article in any other direct way. (I read that he complained to Schrödinger about that article for indirectly supporting Einstein in his crusade against QM.)

If he adheres to this passage, then Heisenberg cannot claim that Schrödinger’s cat would be both alive and dead, or that the moon would not be there if nobody watches.

Others, like Christopher A. Fuchs and Asher Peres in "Quantum Theory Needs No Interpretation", are apparently less sure whether (neo-Copenhagen) quantum theory is so clear about that fact. Hence they try to weasel out by claiming: “If Erwin has performed no observation, then there is no reason he cannot reverse Cathy’s digestion and memories. Of course, for that he would need complete control of all the microscopic degrees of freedom of Cathy and her laboratory, but that is a practical problem, not a fundamental one.”

This is non-sense, because the description of the experiment given previously was complete enough to rule out any possibility for Erwin to reverse the situation. Note the relevance of “… a consistent interpretation of QM as applied to what we do in a physical laboratory and how practitioners experience QM in that context.” If Erwin had access to a time machine enabling him to realistically reverse the situation, then it might turn out that Cathy and Erwin indeed lived multiple times through both situations (and experienced real macroscopic superpositions), as depicted in movies like “Back to the Future”.

(... that got posted while still editing my answer...) Here is at least the passage from Heisenberg this references:

… what one may call metaphysical realism. The world, i.e., the extended things, ‘exist’. This is to be distinguished from practical realism, and the different forms of realism may be described as follows: We ‘objectivate’ a statement if we claim that its content does not depend on the conditions under which it can be verified. Practical realism assumes that there are statements that can be objectivated and that in fact the largest part of our experience in daily life consists of such statements. Dogmatic realism claims that there are no statements concerning the material world that cannot be objectivated. Practical realism has always been and will always be an essential part of natural science. Dogmatic realism, however, …