Question: During what time period did relational quantum mechanics start to become studied?
About the article "Quantum mechanics", section "Philosophical implications".

Candidate passages:
 "This article is intended for those already familiar with quantum mechanics and its attendant interpretational difficulties.
Readers who are new to the subject may first want to read the introduction to quantum mechanics."
The relational approach to quantum physics is an alternative approach to and interpretation of quantum mechanics.
It asserts that the physical world can only be studied accurately in terms of "relationships" between systems, as all experimentally verifiable facts about the world result explicitly from interactions (such as the interaction between a light field and a detector).
According to the relational approach, the assumption that objects possess absolute properties (such as an absolute particle, independent of any detection frame) inevitably leads to ambiguities and paradoxes when these objects are studied closely.
The approach was adopted, in a time span of 1992-1996, by Q. Zheng, S. Hughes, and T. Kobayashi in the University of Tokyo.
As early as in 1985, S. Kochen suggested that the paradoxes of quantum physics could be overcome by developing a relational approach, which was needed at one time to solve the paradoxes of relativistic physics of space and time.
It is also hoped that this entry will serve as a complement to Rovelli’s relational quantum mechanics (RQM).
Historically, the theory of relativity and quantum mechanics were intertwined with each other and the compatibility between both theories was a main theme throughout the Bohr-Einstein debate.
In both theories the physicists emphasized that only measurable quantities, that is, observables, belong in a theory.
Bohr compared his approach to Einstein’s theory of relativity and asserted that in the treatment of quantum processes the complementarity of the measuring results cannot be ignored, just as in high-speed phenomena the relativity of observation cannot be neglected when the simultaneity comes into question.
But Einstein replied: “A good joke should not be repeated too often.” The debate continued in connection with Einstein-Podolsky-Rosen (EPR) paradox, and Bohr proposed the relational conception of quantum states.
Through their analysis Bohm and Schumacher concluded that the characteristic feature of this debate is the failure to communicate due to the absence of a full harmony of quantum mechanics with relativity.
Modern attempts to embrace a relational approach with interpretations of quantum mechanics have been tried many times, ranging from Everett's relative-state interpretation (Everett, 1957), sigma algebra of interactive properties (Kochen, 1979), quantum reference systems (Bene, 1992), quantum theory of the universe (Smolin, 1995), to relational quantum mechanics (Rovelli, 1996).
They more or less emphasize the relational nature of quantum states.
For more information, please refer to the further reading list. 
Natural sciences.
The Scientific Revolution is a convenient boundary between ancient thought and classical physics.
Nicolaus Copernicus revived the heliocentric model of the solar system described by Aristarchus of Samos.
This was followed by the first known model of planetary motion given by Kepler in the early 17th century, which proposed that the planets follow elliptical orbits, with the Sun at one focus of the ellipse.
Galileo (""Father of Modern Physics"") also made use of experiments to validate physical theories, a key element of the scientific method.
In 1687, Isaac Newton published the "Principia Mathematica", detailing two comprehensive and successful physical theories: Newton's laws of motion, which led to classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity.
The behavior of electricity and magnetism was studied by Faraday, Ohm, and others during the early 19th century.
These studies led to the unification of the two phenomena into a single theory of electromagnetism, by James Clerk Maxwell (known as Maxwell's equations).
The beginning of the 20th century brought the start of a revolution in physics.
The long-held theories of Newton were shown not to be correct in all circumstances.
Beginning in 1900, Max Planck, Albert Einstein, Niels Bohr and others developed quantum theories to explain various anomalous experimental results, by introducing discrete energy levels.
Not only did quantum mechanics show that the laws of motion did not hold on small scales, but even more disturbingly, the theory of general relativity, proposed by Einstein in 1915, showed that the fixed background of spacetime, on which both Newtonian mechanics and special relativity depended, could not exist.
In 1925, Werner Heisenberg and Erwin Schrödinger formulated quantum mechanics, which explained the preceding quantum theories.
The observation by Edwin Hubble in 1929 that the speed at which galaxies recede positively correlates with their distance, led to the understanding that the universe is expanding, and the formulation of the Big Bang theory by Georges Lemaître.
Further developments took place during World War II, which led to the practical application of radar and the development and use of the atomic bomb.
Though the process had begun with the invention of the cyclotron by Ernest O. Lawrence in the 1930s, physics in the postwar period entered into a phase of what historians have called "Big Science", requiring massive machines, budgets, and laboratories in order to test their theories and move into new frontiers.
The primary patron of physics became state governments, who recognized that the support of "basic" research could often lead to technologies useful to both military and industrial applications.
Currently, general relativity and quantum mechanics are inconsistent with each other, and efforts are underway to unify the two. 
In physics and philosophy, a relational theory is a framework to understand reality or a physical system in such a way that the positions and other properties of objects are only meaningful relative to other objects.
In a relational spacetime theory, space does not exist unless there are objects in it; nor does time exist without events.
The relational view proposes that space is contained in objects and that an object represents within itself relationships to other objects.
Space can be defined through the relations among the objects that it contains considering their variations through time.
The alternative spatial theory is an absolute theory in which the space exists independently of any objects that can be immersed in it.
Someone who has constructed a relational theory or promotes relational theorising is called a relationist.
The relational point of view was advocated by in physics by Gottfried Wilhelm Leibniz, Ernst Mach (in his Mach's principle), and it was rejected by Isaac Newton in his successful description of classical physics.
Although Albert Einstein was impressed by Mach's principle, he did not fully incorporate it into his theory of general relativity.
Several attempts have been made to formulate a full Machian theory, but most physicists think that none have so far succeeded.
For example, see Brans–Dicke theory.
Relational quantum mechanics and a relational approach to quantum physics have been independently developed, in analogy with Einstein's special relativity of space and time.
Relationist physicists such as John Baez and Carlo Rovelli have criticised the leading unified theory of gravity and quantum mechanics, string theory, as retaining absolute space.
Some prefer a developing theory of gravity, loop quantum gravity for its 'backgroundlessness'.
A recent synthesis of relational theory, called R-theory, continuing the work of the mathematical biologist Robert Rosen (who developed "Relational Biology" and "Relational Complexity" as theories of life () takes a position between the above views.
Rosen's theory differed from other relational views in defining fundamental relations in nature (as opposed to merely epistemic relations we might discuss) as information transfers between natural systems and their organization (as expressed in models).
R-theory extends the idea of organizational models to nature generally.
As interpreted by R-theory, such "modeling relations" describe reality in terms of information relations (encoding and decoding) between measurable existence (expressed as material states and established by efficient behavior) and implicate organization or identity (expressed as formal potential and established by final exemplar), thus capturing all four of Aristotle's causalities within nature (Aristotle defined final cause as immanent from outside of nature).
Applied to space-time physics, it claims that space-time is real but established only in relation to existing events, as a formal cause or model for the location of events relative to each other; and in reverse a system of space-time events establishes a template for space-time.
R-theory is thus a form of model-dependent realism.
It claims to more closely follow the views of Mach, Leibniz, Wheeler and Bohm, suggesting that natural law itself is system-dependent. 
The essential idea behind relational quantum mechanics, following the precedent of special relativity, is that different observers may give different accounts of the same series of events: for example, to one observer at a given point in time, a system may be in a single, "collapsed" eigenstate, while to another observer at the same time, it may be in a superposition of two or more states.
Consequently, if quantum mechanics is to be a complete theory, relational quantum mechanics argues that the notion of "state" describes not the observed system itself, but the relationship, or correlation, between the system and its observer(s).
The state vector of conventional quantum mechanics becomes a description of the correlation of some "degrees of freedom" in the observer, with respect to the observed system.
However, it is held by relational quantum mechanics that this applies to all physical objects, whether or not they are conscious or macroscopic.
Any "measurement event" is seen simply as an ordinary physical interaction, an establishment of the sort of correlation discussed above.
Thus the physical content of the theory has to do not with objects themselves, but the relations between them.
An independent relational approach to quantum mechanics was developed in analogy with David Bohm's elucidation of special relativity, in which a detection event is regarded as establishing a relationship between the quantized field and the detector.
The inherent ambiguity associated with applying Heisenberg's uncertainty principle is subsequently avoided. 
Quantum Bayesianism is an alternative to the (more) popular Copenhagen interpretation of quantum mechanics, which is built upon the idea of wavefunction collapse.
The Copenhagen interpretation does not assume a specific interpretation of probability.
A related attempt is to derive physics from Fisher information, described in Roy Frieden's book titled "Physics from Fisher Information".
However, his claims do not stand up to a close examination.
Other approaches to quantum mechanics are broadly related in that they also treat quantum states as expressions of information, knowledge, belief, or expectation.
All these approaches - including QBism - can be termed "psi-epistemic", but they differ in what they consider quantum states to be information or expectations 'about', as well as in the technical features of the mathematics they employ.
Comparisons have also been made between QBism and the relational quantum mechanics espoused by Carlo Rovelli and others.QBism should be distinguished from other applications of Bayesian probability in quantum physics.
For example, quantum computer science uses Bayesian networks, which find applications in "medical diagnosis, monitoring of processes, and genetics".
(A Bayesian framework is also used for neural networks.)
Bayesian inference has also been applied in quantum theory in terms of probability densities over quantum states, and MaxEnt methods have been used in similar ways.