Brigitte Falkenburg, TU Dortmund

Leuchs-Russell-Auditorium, A.1.500, Staudtstr. 2

Location details

Abstract:

In astronomy, since Galileo, the light of the planets, moons, and stars has been metaphorically termed cosmic messengers carrying information from the celestial bodies to Earth. This metaphor still underlies the heuristic talk of cosmic messengers in astroparticle physics (APP). Here, the cosmic messengers are quantum processes in which cosmic rays made up of subatomic particles transfer information from cosmic sources to terrestrial particle detectors. The heuristic talk of messenger particles and the underlying model of information transfer from cosmic sources to the Earth meets the criteria of the philosopher W. Salmon (1997) for a causal-mechanistic explanation. The causal mechanism consists in the transfer of a conserved physical quantity, such as energy, from one object to another; here: from a cosmic source to a particle detector on Earth. In APP, this process is modelled in several steps, from the production of high-energy protons, e.g. due to the explosion of a supernova, to their acceleration by plasma shock waves, the secondary production of high-energy neutrinos and photons, and their propagation through the universe including their reactions during the passage through interstellar gas and magnetic fields, to their registration by a particle detector on Earth. In the absence of a unified fundamental theory of physics, these steps are described by several models with different theoretical foundations.

The talk addresses the many facets of this causal-mechanistic explanation for two cases: (1) the neutrino signal measured in 2017 by the IceCube detector in Antarctica (IceCube Collab. 2018), and (2) the signals traced back to the galactic disc (IceCube Collab. 2021, 2023). A special feature of the Ice Cube measurements is the probabilistic character of the causal-mechanistic explanation employed in it. The data analysis determines the origin of the measured signal directly from the raw data using probabilistic methods of machine learning, without reconstructing individual particle tracks, as customary in the high-energy scattering experiments of particle physics (e.g. at the LHC). To what extent and in what sense may we still speak of single causal processes here? With what justification did the physicists locate the origin of the neutrino signal in the galactic disc, tacitly interpreting the signal and its cause in terms of scientific realism? In contrast, for the 2017 neutrino signal, an important element of the interpretation was the coincidence with the high-energy gamma ray activity of the blazar TXS 0506+056, which supported the hypothesis of the following causal process: A supermassive black hole emitted two jets; the high-energy protons in the jets, which did not reach Earth due to their deflection by magnetic fields, produced neutrinos and high-energy photons that led to the coincident measurements. In my talk I will analyse the underlying assumptions of scientific realism and their justification.