More questions about how the loop quantum gravity case is different or peculiar with respect to other formalisms or other physical systems [less exotic that quantum gravity), with respect to the application and role and interpretation of decoherence. Answer from speaker: indeed, it may be not so peculiar, but the role of decoherence [how superposition is suppressed, how a special set of observables is selected] in this context remains most interesting.

Suggestion from the audience: may be interesting to look at work on “temporal decoherence”.

Butterfield: the main point of decoherence is that when we model the interaction with the environment, the suppression of superposition [diagonalization] is rapid and inevitable; indeed, which is the selected basis and which correlations are suppressed is not given by the theory and is to some extent a choice in modelling of the system. Sudarsky: true, but there exists contexts [cosmology] where no experimenter and no observer can be associated with that “choice”.

Stressing how the way decoherence works is, to some extent, up to us, in the sense that it depends on the choice of what are the degrees of freedom that one treats as environment and which ones one treats as “the system” that should decohere. Some discussion with the audience on how much freedom one really has, or, more bluntly, on whether the whole process is “observer-dependent” and up to the conscious choice of the physicist.

Mention of the possibility to use ideas from condensed matter, where decoherence also plays an important role.

Issue is superposition of spin networks, as basis states of the Hilbert space of the theory. Decoherence can be applied to deal with [and suppress] this superposition.

Move on to application of decoherence in gravitational setting, i.e. in the context in which coupling with metric [gravitational field] is taken into account. From here, to the context in which the same field is quantized: loop quantum gravity

Decoherence also suggests an explanation of why special bases (e.g. positions or energy levels) are “preferred” in given physical situations, again in terms of the coupling with the environment (which includes the measurement apparatus).