Quantum Theory Without Quantum States
27 January - 27 March 2025
Biography
Guido Bacciagaluppi is a philosopher of physics, trained at ETH Zürich and Cambridge. He mainly works on quantum mechanics, with further interests in the philosophy of probability and the wider philosophy of science. Over the years, he has also acquired a reputation as a historian of quantum mechanics specialising in the history of the foundational debates.
In the philosophy of quantum mechanics, he takes no sides in the debates among the various approaches to the theory, and has worked on modal interpretations, stochastic mechanics, Everett theory, de Broglie-Bohm pilot-wave theory and spontaneous collapse theories, with a special interest in the theory of decoherence.
In history, he has published with Antony Valentini a well-received monograph on the 1927 Solvay conference; he is an active contributor to the renaissance of interest in Grete Hermann, in particular through a volume with Elise Crull; he is one of the editors of the Oxford Handbook of the History of Quantum Interpretations; and he has just published another monograph with Elise, The Einstein Paradox: The debate on nonlocality and incompleteness in 1935.
Until recently, he was Co-Editor-in-Chief of the Journal for General Philosophy of Science and he is on the standing committees for the two conference series Foundations of Physics and New Directions in the Philosophy of Physics. He is also Trustee and Secretary of the Bristol-based Archive for Mathematical Sciences and Philosophy, which looks after some 40’000 audio and video recordings of seminars and conferences in physics, mathematics and philosophy of science going back to 1973.
His permanent base is at the Freudenthal Institute and Descartes Centre at Utrecht University, where he teaches for the Master’s in History and Philosophy of Science and leads a 6-strong ERC-funded research group working on Niels Bohr’s philosophical legacy.
Research Summary
Guido Bacciagaluppi is looking forward to collaborating with Karim Thébault and other colleagues in philosophy and physics at Bristol on a new project aiming to reconceptualise quantum physics without using a fundamental notion of quantum states to define probabilities, and instead treating conditional probabilities as fundamental. Such a view arguably has its historical roots in the way Heisenberg thought of his own matrix mechanics in opposition to Schrödinger’s wave mechanics. Especially within the philosophy of quantum mechanics Schrödinger’s wave functions (or quantum states) are standardly reified as the ‘stuff’ that is ‘out there’ and that we need to make sense of. There are indications, however, that it may be possible to remove quantum states from the formalism entirely (coming both from time-symmetrical approaches in so-called spontaneous collapse approaches to quantum mechanics, and from the maximally mixed character of the quantum field theory .vacuum in any bounded region of spacetime).
The proposed research will explore the general viability of this idea, both from a technical angle and by generalising it to all interpretational approaches to quantum theory. Bristol is an ideal place to explore such novel ideas because of the high concentration both of philosophers of physics (K. Thébault, J. Ladyman, L. Zuchowski, J. Steeger) and of physicists working in the foundations of quantum mechanics (S. Popescu, T. Short).
The Visiting Professorship will have a number of auxiliary objectives, both in terms of furthering other ongoing projects, and in view of instituting a longer-term relation with the Department of Philosophy at Bristol. This will not only involve research but will include sharing teaching materials and experience, and be of direct use to students.
During his visit, Dr Bacciagaluppi plans to deliver a public lecture on his ERC project ‘Niels Bohr for the 21st Century’ and a departmental seminar on the philosophy of probability titled ‘Unscrambling subjective and epistemic probabilities’, and he is keen to contribute a series of guest lectures in philosophy of physics at graduate or advanced undergraduate level.
Dr Bacciagaluppi's lectures will be listed on our Events page in due course.
You can contact his host Dr Karim Thebault for further information.
