40 research outputs found
Non-realism : deep thought or a soft option ?
The claim that the observation of a violation of a Bell inequality leads to
an alleged alternative between nonlocality and non-realism is annoying because
of the vagueness of the second term.Comment: 5 page
Einstein, incompleteness, and the epistemic view of quantum states
Does the quantum state represent reality or our knowledge of reality? In
making this distinction precise, we are led to a novel classification of hidden
variable models of quantum theory. Indeed, representatives of each class can be
found among existing constructions for two-dimensional Hilbert spaces. Our
approach also provides a fruitful new perspective on arguments for the
nonlocality and incompleteness of quantum theory. Specifically, we show that
for models wherein the quantum state has the status of something real, the
failure of locality can be established through an argument considerably more
straightforward than Bell's theorem. The historical significance of this result
becomes evident when one recognizes that the same reasoning is present in
Einstein's preferred argument for incompleteness, which dates back to 1935.
This fact suggests that Einstein was seeking not just any completion of quantum
theory, but one wherein quantum states are solely representative of our
knowledge. Our hypothesis is supported by an analysis of Einstein's attempts to
clarify his views on quantum theory and the circumstance of his otherwise
puzzling abandonment of an even simpler argument for incompleteness from 1927.Comment: 18 pages, 8 figures, 1 recipe for cupcakes; comments welcom
First Order Kaon Condensation in Neutron Stars: Finite Size Effects in the Mixed Phase
We study the role of Coulomb and surface effects on the phase transition from
dense nuclear matter to a mixed phase of nuclear and kaon-condensed matter. We
calculate corrections to the bulk calculation of the equation of state (EOS)
and the critical density for the transition by solving explicitly for
spherical, cylindrical, and planar structures. The importance of Debye
screening in the determination of the charged particle profiles is studied in
some detail. We find that the surface and Coulomb contributions to the energy
density are small, but that they play an important role in the determination of
the critical pressure for the transition, as well as affecting the size and
geometry of favored structures. This changes the EOS over a wide range of
pressure and consequently increases the maximum mass by about 0.1 solar masses.
Implications for transport properties of the mixed phase are also discussed.Comment: 18 pages, 6 figure
Causarum Investigatio and the Two Bell's Theorems of John Bell
"Bell's theorem" can refer to two different theorems that John Bell proved,
the first in 1964 and the second in 1976. His 1964 theorem is the
incompatibility of quantum phenomena with the joint assumptions of Locality and
Predetermination. His 1976 theorem is their incompatibility with the single
property of Local Causality. This is contrary to Bell's own later assertions,
that his 1964 theorem began with the assumption of Local Causality, even if not
by that name. Although the two Bell's theorems are logically equivalent, their
assumptions are not. Hence, the earlier and later theorems suggest quite
different conclusions, embraced by operationalists and realists, respectively.
The key issue is whether Locality or Local Causality is the appropriate notion
emanating from Relativistic Causality, and this rests on one's basic notion of
causation. For operationalists the appropriate notion is what is here called
the Principle of Agent-Causation, while for realists it is Reichenbach's
Principle of common cause. By breaking down the latter into even more basic
Postulates, it is possible to obtain a version of Bell's theorem in which each
camp could reject one assumption, happy that the remaining assumptions reflect
its weltanschauung. Formulating Bell's theorem in terms of causation is
fruitful not just for attempting to reconcile the two camps, but also for
better describing the ontology of different quantum interpretations and for
more deeply understanding the implications of Bell's marvellous work.Comment: 24 pages. Prepared for proceedings of the "Quantum [Un]speakables II"
conference (Vienna, 2014), to be published by Springe
Neutrino Opacities in Neutron Stars with Kaon Condensates
The neutrino mean free paths in hot neutron-star matter are obtained in the
presence of kaon condensates. The kaon-induced neutrino absorption process,
which is allowed only in the presence of kaon condensates, is considered for
both nondegenerate and degenerate neutrinos. The neutrino mean free path due to
this process is compared with that for the neutrino-nucleon scattering. While
the mean free path for the kaon-induced neutrino absorption process is shown to
be shorter than the ordinary two-nucleon absorption process by several orders
of magnitude when temperature is not very high, the neutrino-nucleon scattering
process has still a dominant contribution to the neutrino opacity. Thus, the
kaon-induced neutrino absorption process has a minor effect on the thermal and
dynamical evolution of protoneutron stars.Comment: 35 pages, 4 figure
Free Will in a Quantum World?
In this paper, I argue that Conway and Kochen’s Free Will Theorem (1,2) to the conclusion that quantum mechanics and relativity entail freedom for the particles, does not change the situation in favor of a libertarian position as they would like. In fact, the theorem more or less implicitly assumes that people are free, and thus it begs the question. Moreover, it does not prove neither that if people are free, so are particles, nor that the property people possess when they are said to be free is the same as the one particles possess when they are claimed to be free. I then analyze the Free State Theorem (2), which generalizes the Free Will Theorem without the assumption that people are free, and I show that it does not prove anything about free will, since the notion of freedom for particles is either inconsistent, or it does not concern our common understanding of freedom. In both cases, the Free Will Theorem and the Free State Theorem do not provide any enlightenment on the constraints physics can pose on free will
Realism about the Wave Function
A century after the discovery of quantum mechanics, the meaning of quantum
mechanics still remains elusive. This is largely due to the puzzling nature of
the wave function, the central object in quantum mechanics. If we are realists
about quantum mechanics, how should we understand the wave function? What does
it represent? What is its physical meaning? Answering these questions would
improve our understanding of what it means to be a realist about quantum
mechanics. In this survey article, I review and compare several realist
interpretations of the wave function. They fall into three categories:
ontological interpretations, nomological interpretations, and the \emph{sui
generis} interpretation. For simplicity, I will focus on non-relativistic
quantum mechanics.Comment: Penultimate version for Philosophy Compas
Bell-Type Quantum Field Theories
In [Phys. Rep. 137, 49 (1986)] John S. Bell proposed how to associate
particle trajectories with a lattice quantum field theory, yielding what can be
regarded as a |Psi|^2-distributed Markov process on the appropriate
configuration space. A similar process can be defined in the continuum, for
more or less any regularized quantum field theory; such processes we call
Bell-type quantum field theories. We describe methods for explicitly
constructing these processes. These concern, in addition to the definition of
the Markov processes, the efficient calculation of jump rates, how to obtain
the process from the processes corresponding to the free and interaction
Hamiltonian alone, and how to obtain the free process from the free Hamiltonian
or, alternatively, from the one-particle process by a construction analogous to
"second quantization." As an example, we consider the process for a second
quantized Dirac field in an external electromagnetic field.Comment: 53 pages LaTeX, no figure
Quantum Locality
It is argued that while quantum mechanics contains nonlocal or entangled
states, the instantaneous or nonlocal influences sometimes thought to be
present due to violations of Bell inequalities in fact arise from mistaken
attempts to apply classical concepts and introduce probabilities in a manner
inconsistent with the Hilbert space structure of standard quantum mechanics.
Instead, Einstein locality is a valid quantum principle: objective properties
of individual quantum systems do not change when something is done to another
noninteracting system. There is no reason to suspect any conflict between
quantum theory and special relativity.Comment: Introduction has been revised, references added, minor corrections
elsewhere. To appear in Foundations of Physic
Embedding Quantum Mechanics Into a Broader Noncontextual Theory: A Conciliatory Result
The extended semantic realism (ESR) model embodies the mathematical formalism
of standard (Hilbert space) quantum mechanics in a noncontextual framework,
reinterpreting quantum probabilities as conditional instead of absolute. We
provide here an improved version of this model and show that it predicts that,
whenever idealized measurements are performed, a modified
Bell-Clauser-Horne-Shimony-Holt (BCHSH) inequality holds if one takes into
account all individual systems that are prepared, standard quantum predictions
hold if one considers only the individual systems that are detected, and a
standard BCHSH inequality holds at a microscopic (purely theoretical) level.
These results admit an intuitive explanation in terms of an unconventional kind
of unfair sampling and constitute a first example of the unified perspective
that can be attained by adopting the ESR model.Comment: 24 pages, standard Latex, Extensively revised versio