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These essays are based on lectures on the foundation of quantum theory, symmetries and representation theory, and the quantum theory of the superworld. The author examines the quantum world and superworld under the lens of symmetry and supersymmetry.

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This is a collection of essays based on lectures that author has given on various occasions on foundation of quantum theory, symmetries and representation theory, and the quantum theory of the superworld created by physicists.
The lectures are linked by a unifying theme: how the quantum world and superworld appear under the lens of symmetry and supersymmetry.
In the world of ultra-small times and distances such as the Planck length and Planck time, physicists believe no measurements are possible and so the structure of spacetime itself is an unknown that has to be first understood. There have been suggestions (Volovich hypothesis) that world geometry at such energy regimes is non-archimedian and some of the lectures explore the consequences of such a hypothesis.
Ultimately, symmetries and supersymmetries are described by the representation of groups and supergroups. The author´s interest in representation is a lifelong one and evolved slowly, and owes a great deal to conversations and discussions he had with George Mackey and Harish-Chandra. The book concludes with a retrospective look at these conversations.

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Prologue.- Quantum foundations.- Quantum measurement.- Probability in the quantum world.- Spacetime in the ultra-small scale.- The superworld.- Symmetries and particles in the p-adic world.- Representation theory: Conversations with Harish-Chandra.

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The author writes: "Most of my thoughts on quantum theory are in these essays. The last section is on represenation theory. I do not like to call it an epilogue bucause it deals with a large part of what I have done in this area over the years...I have been thinking about a collection like this for many years that will bring together the many lectures I have given in various places."

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