dorsal/arxiv
View SchemaWhy quantum dynamics is linear
| Authors | Thomas F. Jordan |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/0702171 |
| URL | https://arxiv.org/abs/quant-ph/0702171 |
| DOI | 10.1088/1742-6596/196/1/012010 |
| Journal | J.Phys.Conf.Ser.196:012010,2009 |
Abstract
Quantum dynamics is linear. How do we know? From theory or experiment? The history of this question is reviewed. Nonlinear generalizations of quantum mechanics have been proposed. They predict small but clear nonlinear effects, which very accurate experiments have not seen. Is there a reason in principle why nonlinearity is not found? Is it impossible? Does quantum dynamics have to be linear? Attempts to prove this have not been decisive, because either their assumptions are not compelling or their arguments are not conclusive. The question has been left unsettled. There is a simple answer, based on a simple assumption. It was found in two steps separated by 44 years. They are steps back to simpler and more compelling assumptions. A proof of the assumptions of the Wigner-Bargmann proof has been known since 1962. It assumes that the maps of density matrices in time are linear. For this step, it is also assumed that density matrices are mapped one-to-one onto density matrices. An alternative is to assume that pure states are mapped one-to-one onto pure states and that entropy does not decrease. In a step taken in 2006, it is proved that the maps of density matrices in time are linear. It is assumed, as in the earlier step, that at each time the physical quantities and states are described by the usual linear structures of quantum mechanics, so the question is only about how things change in time. Beyond that, the proof assumes only that the dynamics does not depend on anything outside the system, but must allow the system to be described as part of a larger system.
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"abstract": "Quantum dynamics is linear. How do we know? From theory or experiment? The\nhistory of this question is reviewed. Nonlinear generalizations of quantum\nmechanics have been proposed. They predict small but clear nonlinear effects,\nwhich very accurate experiments have not seen. Is there a reason in principle\nwhy nonlinearity is not found? Is it impossible? Does quantum dynamics have to\nbe linear? Attempts to prove this have not been decisive, because either their\nassumptions are not compelling or their arguments are not conclusive. The\nquestion has been left unsettled. There is a simple answer, based on a simple\nassumption. It was found in two steps separated by 44 years. They are steps\nback to simpler and more compelling assumptions. A proof of the assumptions of\nthe Wigner-Bargmann proof has been known since 1962. It assumes that the maps\nof density matrices in time are linear. For this step, it is also assumed that\ndensity matrices are mapped one-to-one onto density matrices. An alternative is\nto assume that pure states are mapped one-to-one onto pure states and that\nentropy does not decrease. In a step taken in 2006, it is proved that the maps\nof density matrices in time are linear. It is assumed, as in the earlier step,\nthat at each time the physical quantities and states are described by the usual\nlinear structures of quantum mechanics, so the question is only about how\nthings change in time. Beyond that, the proof assumes only that the dynamics\ndoes not depend on anything outside the system, but must allow the system to be\ndescribed as part of a larger system.",
"arxiv_id": "quant-ph/0702171",
"authors": [
"Thomas F. Jordan"
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"doi": "10.1088/1742-6596/196/1/012010",
"journal_ref": "J.Phys.Conf.Ser.196:012010,2009",
"title": "Why quantum dynamics is linear",
"url": "https://arxiv.org/abs/quant-ph/0702171"
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