Quantum Philosophy (book)
Encyclopedia
Quantum Philosophy is a book by the physicist Roland Omnès
, in which he aims to show the non-specialist reader how modern developments in quantum mechanics
allow the recovery of our common sense view of the world.
As Omnès makes explicit, this is the exact opposite of the classical epistemological project. It has always, up to now, been necessary to access reality by first presupposing the laws of classical common sense. Now finally, we can enter the world either at the formal level, or at the classical level, and we find that each entails the other: experiment has led to the quantum formalism; the quantum formalism now, finally, allows the recovery of the framework of classical reasoning under which the experiments took place.
Omnès emphasises throughout that no new principles, other than those described when quantum mechanics was developed in the 1920’s, are needed. Moreover, some additional principles which seemed to be required then (such as wavefunction collapse
, or its slightly more formal sister, wavefunction reduction) are no longer needed. Classical behaviour can now be recovered in a system described entirely by a single, unitary
(time-reversible) wavefunction.
The mathematical developments which allowed this progress have taken place in two fields: quantum decoherence
and the consistent histories
approach to quantum mechanics.
The consistent histories approach makes mathematically explicit which sets of classical questions can be consistently asked of a single quantum system, and, conversely, which sets of questions are fundamentally inconsistent, and thus meaningless when asked together. We can therefore demonstrate formally why it is that the questions which Einstein, Podolsky and Rosen
assumed could be asked together, of a single quantum system, simply cannot be asked together. On the other hand, we can demonstrate that classical, logical reasoning often does apply, even to quantum experiments – but we can now be mathematically exact about the limits of classical logic.
Quantum decoherence, on the other hand (in combination with the consistent histories approach), recovers classical behaviour at the macroscopic level. The formal mathematics of this approach allows us to demonstrate, finally, that is impossible (or rather, massively improbable) for a macroscopic Schrödinger's cat
to exist for longer than a minuscule time (related to the macroscopic energy dissipation time by a factor involving the square of Planck's constant) in a quantum superposition of its |alive> and |dead> states. Even for a cat otherwise isolated from the rest of the Universe, and even with no observer present, there are so many unknowns in the quantum state of the whole cat, that the relevant mathematics determine that only the normally observed classical states of the cat are at all probable, except over the very shortest of timescales. This reasoning is developed formally within measurement theory
, and applies to any macroscopic, non-super cooled measuring device, whether or not there is an observer to watch it.
, Murray Gell-Mann
, and James Hartle
.
Roland Omnès
Roland Omnès is the author of several books which aim to close the gap between our common sense experience of the classical world and the complex, formal mathematics which is now required to accurately describe reality at its most fundamental level.- Biography :Omnès is currently Professor...
, in which he aims to show the non-specialist reader how modern developments in quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
allow the recovery of our common sense view of the world.
Book contents
- Section I - a review of mathematics, epistemology and science from the classical to the early modern period.
- Section II - a review of the ineluctable rise of formalism in mathematics and in fundamental physical science, which, Omnès argues, was not a choice, but was forced on researchers by the nature of the subject matter.
- Section III - the central section of the book, in which the recovery of common sense, as outlined below, is presented.
- Section IV - a short section of reflections on possible future steps.
Brief summary of Omnès' Central Argument
Omnès' project is not quite as it at first sounds. He is not trying to show that quantum mechanics itself can be understood in a common sense framework, quite the opposite. He argues that modern science has, necessarily, become more and more formal, and more and more remote from common sense, as it strives to make itself an accurate reflection of the physical world. But he argues that we have now come near enough to scaling the 'magnificent peaks' of the formal mathematics needed to describe reality for one thing to have finally become clear: it is now possible to demonstrate, formally, and starting from the underlying principles of quantum mechanics, that the laws of classical logic, classical probability and classical dynamics apply to objects at the macroscopic level.As Omnès makes explicit, this is the exact opposite of the classical epistemological project. It has always, up to now, been necessary to access reality by first presupposing the laws of classical common sense. Now finally, we can enter the world either at the formal level, or at the classical level, and we find that each entails the other: experiment has led to the quantum formalism; the quantum formalism now, finally, allows the recovery of the framework of classical reasoning under which the experiments took place.
Omnès emphasises throughout that no new principles, other than those described when quantum mechanics was developed in the 1920’s, are needed. Moreover, some additional principles which seemed to be required then (such as wavefunction collapse
Wavefunction collapse
In quantum mechanics, wave function collapse is the phenomenon in which a wave function—initially in a superposition of several different possible eigenstates—appears to reduce to a single one of those states after interaction with an observer...
, or its slightly more formal sister, wavefunction reduction) are no longer needed. Classical behaviour can now be recovered in a system described entirely by a single, unitary
Unitary
Unitary may refer to:* Unitary construction, in automotive design, another common term for a unibody or monocoque construction**Unitary as chemical weapons opposite of Binary...
(time-reversible) wavefunction.
The mathematical developments which allowed this progress have taken place in two fields: quantum decoherence
Quantum decoherence
In quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. A consequence of this dephasing leads to classical or probabilistically additive behavior...
and the consistent histories
Consistent histories
In quantum mechanics, the consistent histories approach is intended to give a modern interpretation of quantum mechanics, generalising the conventional Copenhagen interpretation and providing a natural interpretation of quantum cosmology...
approach to quantum mechanics.
The consistent histories approach makes mathematically explicit which sets of classical questions can be consistently asked of a single quantum system, and, conversely, which sets of questions are fundamentally inconsistent, and thus meaningless when asked together. We can therefore demonstrate formally why it is that the questions which Einstein, Podolsky and Rosen
EPR paradox
The EPR paradox is a topic in quantum physics and the philosophy of science concerning the measurement and description of microscopic systems by the methods of quantum physics...
assumed could be asked together, of a single quantum system, simply cannot be asked together. On the other hand, we can demonstrate that classical, logical reasoning often does apply, even to quantum experiments – but we can now be mathematically exact about the limits of classical logic.
Quantum decoherence, on the other hand (in combination with the consistent histories approach), recovers classical behaviour at the macroscopic level. The formal mathematics of this approach allows us to demonstrate, finally, that is impossible (or rather, massively improbable) for a macroscopic Schrödinger's cat
Schrödinger's cat
Schrödinger's cat is a thought experiment, usually described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The scenario presents a cat that might be...
to exist for longer than a minuscule time (related to the macroscopic energy dissipation time by a factor involving the square of Planck's constant) in a quantum superposition of its |alive> and |dead> states. Even for a cat otherwise isolated from the rest of the Universe, and even with no observer present, there are so many unknowns in the quantum state of the whole cat, that the relevant mathematics determine that only the normally observed classical states of the cat are at all probable, except over the very shortest of timescales. This reasoning is developed formally within measurement theory
Measurement in quantum mechanics
The framework of quantum mechanics requires a careful definition of measurement. The issue of measurement lies at the heart of the problem of the interpretation of quantum mechanics, for which there is currently no consensus....
, and applies to any macroscopic, non-super cooled measuring device, whether or not there is an observer to watch it.
Collaborators
Omnès makes clear that others contributed materially to the research described in his book, including Robert GriffithsRobert Griffiths (physicist)
Robert B. Griffiths is an American physicist at Carnegie Mellon University. He is the originator of the consistent histories approach to quantum mechanics, which has since been developed by himself, Roland Omnès, Murray Gell-Mann, and James Hartle.Throughout his career, Dr. Robert B...
, Murray Gell-Mann
Murray Gell-Mann
Murray Gell-Mann is an American physicist and linguist who received the 1969 Nobel Prize in physics for his work on the theory of elementary particles...
, and James Hartle
James Hartle
James Burkett Hartle is an American physicist. He has been a professor of physics at the University of California, Santa Barbara since 1966, and he is currently a member of the external faculty of the Santa Fe Institute...
.