Qiss

Quantum gravitational tunneling effects are expected to give rise to a number of interesting observable phenomena, including, in particular, the evolution of black holes at the end of their existence or the emergence of the early universe from a quantum phase. Covariant Loop Quantum Gravity provides a framework to study these phenomena, yet a precise identification of tunneling processes is still not known. Motivated by this question, we consider a related, simpler case, that of Ponzano-Regge amplitudes: we find a surprising and detailed analogy of a class of simple transition amplitudes with tunneling processes in non-relativistic quantum mechanics.

We point out that conservation of information implies that remnants produced at the end of black hole evaporation should radiate in the low-frequency spectrum. We model this emission and derive properties of the diffuse radiation emitted by an otherwise dark population of such objects. We show that for early universe black holes the frequency and energy density of this radiation, which are in principle measurable, suffice to estimate the remnant density.

This paper is a transcript of the dialogue between Carlo Rovelli and Mike Jackson after Rovelli’s delivery of the 2021 Annual Mike Jackson Lecture, hosted by the Centre for Systems Studies at the University of Hull. The dialogue covers a range of topics, including how Rovelli developed a sense of curiosity in his youth; the connection between his interests in science and politics; the pathology of disciplinary divisions in academia; the value of Bogdanov’s transdisciplinarity; Rovelli’s theory of quantum gravity; the notions of granularity, indeterminism and relationality underpinning quantum mechanics; the role of the observer; mistaken uses of quantum mechanics; relational and network views of the world; how the discipline of Physics is becoming more systemic; the concept of levels of analysis in relation to nature and human inquiry; and the future for humanity.

Carlo Rovelli UWO London Journal: Perspectivas 8 (2023) 282-295

There is a surprising parallel between the conceptual step taken by the theoretical physicists who discovered quantum mechanics in the 1920s and the philosophical work of Alexander Bogdanov. Both were under the direct cultural influence of the ideas of Ernst Mach. Even more surprisingly, there are aspects of the current debate on the physical interpretation of the quantum formalism that closely mirror the Lenin-Bogdanov debate, in particular on the confusion between subjectivity and relationality. It seems to me that the ideas of Alexander Bogdanov can still bring clarity and be fertile today when applied to open issues in the foundations of physics.

As we are at the beginning of the second century of quantum physics, we asked four researchers to share their views on new research directions trying to answer old, yet still open, questions in the foundations of quantum theory.

We argue that the temporal asymmetry of influence is not merely the result of thermodynamics: it is a consequence of the fact that modal structure of the universe must admit only processes which cannot give rise to contradictions. We appeal to the process matrix formalism developed in the field of quantum foundations to characterise processes which are compatible with local free will whilst ruling out contradictions, and argue that this gives rise to ‘consistent chaining’ requirements that explain the temporal asymmetry of influence. We compare this view to the perspectival account of causation advocated by Price and Ramsey.

Quantum nonlocality, generated by strong correlations between entangled systems, defies the classical view of nature based on standard causal reasoning plus physical assumptions. The new frontier of the research on entanglement is to explore quantum correlations in complex networks, involving several parties and generating new striking quantum effects. We present recent advances on the realization of photonic quantum networks.

The `Wigner’s friend’ thought experiment illustrates the puzzling nature of quantum measurement. Časlav Brukner discusses how recent results suggest that in quantum theory the objectivity of measurement outcomes is relative to observation and observer.

We revisit Hawking’s black hole radiation derivation, including the quantum state of the initial matter forming the black hole. We investigate how non-vacuum initial quantum states, at the past of a black hole geometry, influence the black hole radiation observed at future null infinity $( mathcal{I}^+)$. We further classify which of the initial state excitations are distinguishable from one another through measurements on the black hole radiation state. We use Algebraic Quantum Field Theory (AQFT) to provide a clear physical interpretation of the results, in terms of localised operations. We then take a concrete example of a black hole made of one large collapsing excitation of mass $M$ and compare it to a same-mass black hole formed due to the collapse of two smaller excitations, of mass $M/2$ each. We find using our formalism that the two cases yield different radiation states and can in principle be distinguished. Our results provide a mechanism for partial information recovery in evaporating black holes, classify what information is recoverable through stimulated emission, and a concrete understanding of the classification based on the AQFT localisation.