Michel Janssen studied physics and philosophy at the University of Amsterdam and history and philosophy of science at the University of Pittsburgh, where he earned his PhD in 1995. He was an editor at the Einstein Papers Project before joining the School of Physics and Astronomy at the University of Minnesota as a historian of science in 2000. He has also been a regular visitor at the Max Planck Institute for History of Science in Berlin. His research focuses on the genesis of relativity and quantum theory.Anthony Duncan received his PhD in theoretical elementary particle physics in 1975 from the Massachusetts Institute of Technology, under the supervision of Steven Weinberg. Following postdoctoral and junior faculty positions at the Institute for Advanced Study in Princeton and Columbia University in New York, he joined the faculty of the Department of Physics and Astronomy at the University of Pittsburgh in 1981 as Associate Professor of Physics. He has taught a wide range of courses, both at the undergraduate and graduate level, including courses on the history of modern physics. He is now (since 2015) Professor Emeritus of Physics at the University of Pittsburgh.

At the top of the scaffold, the arch! In Volume 1, Duncan and Janssen told the intricate story of the long struggles in the first twenty years of the emergence of quantum mechanics. Now, in The Arch, they give a definitive analysis of the climactic and brilliant mid-1920s, with the formulation of matrix and wave mechanics. It is an extraordinary achievement: all future work on this topic starts here.

• 8: Introduction to Volume 2 III. Transition to the New Quantum Theory 9: The Exclusion Principle and Electron Spin 10: Theory in the Old Quantum Theory 11: Umdeutung paper 12: Consolidation of Matrix Mechanics 13: Broglie's Matter Waves and Einstein's Quantum Theory of the Ideal Gas 14: and Wave Mechanics 15: and Failures of the Old Quantum Theory Revisited IV. The Formalism of Quantum Mechanics and Its Statistical Interpretation 16: Interpretation of Matrix and Wave Mechanics 17: Neumann's Hilbert Space Formalism 18: Arch and Scaffold Appendices C. The Mathematics of Quantum Mechanics

Michel Janssen studied physics and philosophy at the University of Amsterdam and history and philosophy of science at the University of Pittsburgh, where he earned his PhD in 1995. He was an editor at the Einstein Papers Project before joining the School of Physics and Astronomy at the University of Minnesota as a historian of science in 2000. He has also been a regular visitor at the Max Planck Institute for History of Science in Berlin. His research focuses on the genesis of relativity and quantum theory.Anthony Duncan received his PhD in theoretical elementary particle physics in 1975 from the Massachusetts Institute of Technology, under the supervision of Steven Weinberg. Following postdoctoral and junior faculty positions at the Institute for Advanced Study in Princeton and Columbia University in New York, he joined the faculty of the Department of Physics and Astronomy at the University of Pittsburgh in 1981 as Associate Professor of Physics. He has taught a wide range of courses, both at the undergraduate and graduate level, including courses on the history of modern physics. He is now (since 2015) Professor Emeritus of Physics at the University of Pittsburgh.

At the top of the scaffold, the arch! In Volume 1, Duncan and Janssen told the intricate story of the long struggles in the first twenty years of the emergence of quantum mechanics. Now, in The Arch, they give a definitive analysis of the climactic and brilliant mid-1920s, with the formulation of matrix and wave mechanics. It is an extraordinary achievement: all future work on this topic starts here.

• 8: Introduction to Volume 2 III. Transition to the New Quantum Theory 9: The Exclusion Principle and Electron Spin 10: Theory in the Old Quantum Theory 11: Umdeutung paper 12: Consolidation of Matrix Mechanics 13: Broglie's Matter Waves and Einstein's Quantum Theory of the Ideal Gas 14: and Wave Mechanics 15: and Failures of the Old Quantum Theory Revisited IV. The Formalism of Quantum Mechanics and Its Statistical Interpretation 16: Interpretation of Matrix and Wave Mechanics 17: Neumann's Hilbert Space Formalism 18: Arch and Scaffold Appendices C. The Mathematics of Quantum Mechanics