Relational quantum mechanics

Because Bob cannot have more than the maximum amount of relevant information about S, if Bob obtains some different information about S, at least some part of the information Alice has about S becomes irrelevant to Bob; he is subsequently unable to access this information, and it will play no role in determining his future interactions with S.

“However, because Bob cannot have more than the maximum amount of relevant information about S , it follows that if Bob obtains some different information about S , at least some part of the information that Alice has about S becomes irrelevant to Bob; that is, he is subsequently unable to access this information, and it will play no role in determining his future interactions with S .”

Subjectivistic interpretations such as relational quantum mechanics, QBism, or the approach in ref. 9 are examples of theories that satisfy (Q) and (S) and thus violate (C).

“Another class of examples are subjectivistic interpretations, which regard statements about outcomes of measurements as personal to an agent, such as “relational quantum mechanics”38, “QBism”39,40, or the approach proposed in ref. 9”

According to Rovelli 1996, the founding principle of RQM is that in quantum mechanics different observers may give different accounts of the same sequence of events.

“According to Rovelli's first paper on the topic (Rovelli 1996), the founding principle of RQM is the idea that 'in quantum mechanics different observers may give different accounts of the same sequence of events.'”

RQM is an interpretation of quantum mechanics based on the idea that quantum states do not describe an absolute property of a system but rather a relationship between systems.

“Relational quantum mechanics (RQM) is an interpretation of quantum mechanics based on the idea that quantum states do not describe an absolute property of a system but rather a relationship between systems.”

Rovelli showed that a significant amount of the structure of standard quantum mechanics can be extracted from the 1996 postulates.

“Rovelli showed that a significant amount of the structure of standard quantum mechanics can be extracted from the 1996 postulates”

In RQM, the term 'observer' is understood in a broad sense, allowing any physical system to be an 'observer,' so consciousness plays no fundamental role.

“in RQM, the term 'observer' is understood in a broad sense, which allows that any physical system can be an 'observer,' so we do not have to accept that consciousness plays any fundamental role.”

Rovelli's original presentation of RQM made use of information-theoretic postulates: 'There is a maximum amount of relevant information that can be extracted from a system' and 'It is always possible to acquire new information about a system.'

“Rovelli's original presentation of RQM made use of several information-theoretic postulates (Rovelli 1996), such as 'There is a maximum amount of relevant information that can be extracted from a system' and 'It is always possible to acquire new information about a system.'”

Different observers may assign different quantum states to a given system, and in such cases all of the different assignations are equally correct because the quantum state assigned to a system describes not only the system itself but also the relation between the system and the observer assigning the state.

“different observers may assign different quantum states to a given system, and moreover, in such cases, all of the different assignations are equally correct because the quantum state assigned to a system describes not only the system itself but also the relation between the system and the observer assigning the state.”

The possibility of destruction of information follows immediately from the combination of the two 1996 postulates: together they imply that sometimes when an agent acquires new information about a system, some of their previous information becomes irrelevant.

“In particular, we note that the possibility of 'destruction of information' follows immediately from the combination of the two 1996 postulates: together they imply that sometimes when an agent acquires new information about a system, some of their previous information becomes irrelevant.”

If Alice is in possession of the maximum amount of relevant information about S, this does not prevent Bob from obtaining some different information about S, provided Bob does not currently have access to Alice's information about S.

“for those postulates tell us that if Alice is in possession of the maximum amount of relevant information about S , which does not prevent Bob from obtaining some different information about S , provided that Bob does not currently have access to Alice's information about S .”

Rovelli's 1996 postulates help us understand why CPL holds only insofar as the relevant information is not disturbed.

“So Rovelli's 1996 postulates help us understand why CPL holds only insofar as the relevant information is not disturbed.”

We can continue to assert that quantum mechanics provides a complete and self-consistent scheme of description of the physical world, appropriate to our present level of experimental observations.

“we can continue to assert that 'quantum mechanics provides a complete Adlam and Rovelli Philosophy of Physics DOI: 10.31389/pop.8 and self-consistent scheme of description of the physical world, appropriate to our present level of experimental observations' (Rovelli 1996),”

The original postulates of RQM set out in Rovelli (1996) together entail that when new information is acquired, part of the old relevant-information becomes irrelevant.

“Furthermore, the original postulates of RQM set out in Rovelli (1996) together entail that 'when new information is acquired, part of the old relevant-information becomes irrelevant.'”

The destruction of information as referenced in CPL must be relativized to an observer.

“The 1996 postulates also help make the point that the 'destruction' of information as referenced in CPL must be relativized to an observer”

Interpretations that reject AOE include QBism, the relational interpretation, and the many-worlds interpretation.

“Interpretations that reject AOE include QBism [6, 7], the relational interpretation [5], and the many-worlds interpretation [4].”