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International Journal of Theoretical Physics
Paul Busch 1955–2018
S. Gudder1
·P. Lahti2
·S. Sozzo3
Received: 8 October 2018 / Accepted: 7 February 2019 /
©Springer Science+Business Media, LLC, part of Springer Nature 2019
(With the courtesy of Elke Busch)
The scientific life of Paul Busch spanned four decades before it came to its untimely
end in 9 June 2018 after a brief illness. Paul was the acting President of the International
Quantum Structures Association, IQSA. He was an outstanding scholar, an exemplary aca-
demician and to many of us a close friend throughout our careers. Paul had been one of
P. Lahti
S. Gudder
S. Sozzo
1University of Denver, Denver, CO, USA
2University of Turku, Turku, Finland
3School of Business and Centre IQSCS, Leicester, UK
International Journal of Theoretical Physics
the driving forces of IQSA and as its elected president in 2016 he was actively involved in
organizing the 14th Biennial IQSA Conference Quantum Structures 2018, the Proceedings
of which is contained in this volume.
Paul was born in Refrath, Germany, BRD, on February 15, 1955. His Alma Mater was
the University of Cologne where he earned his Dr.rer.nat. degree in 1982 and habilitation
in Mathematical Physics in 1985. Paul’s supervisor was Professor Peter Mittelstaedt, who
preceded Paul as the second president of IQSA in 1994–1996.
Paul held numerous academic positions; after his years in Cologne, he served during
1995–2005 as a lecturer, reader, and professor of mathematical physics at the University of
Hull, UK, serving as Head of Department (Mathematics) from 2001–2005. Subsequently,
from 2005 onwards, he was appointed as Professor at the Department of Mathematics of the
University of York. Paul also had a strong connection to the University of Turku, where he
was nominated as an Adjunct Professor of Theoretical Physics in 1991.
Paul was a passionate scientist with keen interest in foundations of quantum mechanics.
Much of his scientific work dealt with the problem of joint measurability of complemen-
tary observables and the relevance of the uncertainty relations to that question. This work
had started with Paul’s doctoral dissertation “Unbestimmtheitsrelation und simultane Mes-
sungen in der Quantentheorie” of 1982, a brief English version of which appeared in this
Journal in 1985, Vo l . 2 4 , No 1, pp 63–92. Paul’s long journey began with his dissertation
and continued to his last submitted article “Measurement uncertainty relations: character-
ising optimal error bounds for qubits”, published in June 2018 in J. Phys. A: Math. Theor.
51 283001 (34pp), with Tom Bullock, Paul’s previous PhD student. His scientific investi-
gations, required an extensive, careful, conceptual mathematical study of all the involved
basic notions: state, measurement, observable, joint measurement, joint observable, com-
plementarity, compatibility, coexistence, characterizations of types of measurements and
limitations posed on them by conservation laws, measurement accuracy, disturbance and
error, the problem of objectification and the measurement problem, all that with detailed
case studies. In addition to the original research papers, the accumulation of knowledge
in these investigations led Paul and his collaborators to write the monographs The Quan-
tum Theory of Measurement (with P Lahti, P Mittelstaedt, Springer, 1991, 2nd rev.ed.
1996), Operational Quantum Physics (with M Grabowski, P Lahti, Springer,1995, 2nd cor-
rected printing 1997), and Quantum Measurement (with P Lahti, J-P Pellonp¨
a, K Ylinen,
Springer, 2016).
His list of scientific publications amounted to over 150 items, with 92 peer reviewed
journal papers. These articles, ranging from 1980 to the present, cover a rich variety of top-
ics, from quantum measurements and quantum structures to development of his cherished
ideas on the concept of unsharp reality. A Special Issue, entitled Paul Busch: At the Heart of
Quantum Mechanics, of Foundations of Physics is devoted to commemorate the scientific
work of Paul. It is scheduled to appear in summer 2019.
This was a man of humility and integrity, who had the highest moral and ethical values
to guide his daily life and scientific work. He was concerned whenever he found that these
moral principles were not appropriately followed. He held his colleagues in high esteem,
young and old alike, and he had a persistent drive to dig out the origins of scientific ideas
and give due credit to their originators. He was a warm and approachable person, with an
extraordinary ability to listen to other people, and he kept his mind open to new ideas. He
never rejected a new or elusive idea without careful and respectful consideration, and he
was always willing to try to jointly refine the proposed ideas. He also readily brought his
own ideas for common deliberation.
International Journal of Theoretical Physics
These remarkable qualities of Paul made him a unique unifying figure among col-
leagues with different backgrounds. He was a loyal friend and an international leader of a
large school of researchers. His committed, passionate dedication to the understanding of
natural phenomena served as a role model that impacted the entire scientific community.
He directly and personally inspired us all. He had reached a pinnacle in his intellectual
growth and we had the promise of even greater contributions in the coming years. He will
be greatly missed.
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