31,304 research outputs found
Implications of the Precautionary Principle for Environmental Regulation in the United States: Examples from the Control of Hazardous Air Pollutants in the 1990 Clean Air Act Amendments
Goldstein and Carruth argue that the hazardous air pollutant provisions of the 1990 Clean Air Act Amendments provide an example of the Precautionary Principle incorporated into US environmental legislation. Evaluating the outcome thus far leads them to the conclusion that utilizing the Precautionary Principle as a basis for legislation can be problematic to public-health goals
Bohmian Mechanics and Quantum Field Theory
We discuss a recently proposed extension of Bohmian mechanics to quantum
field theory. For more or less any regularized quantum field theory there is a
corresponding theory of particle motion, which in particular ascribes
trajectories to the electrons or whatever sort of particles the quantum field
theory is about. Corresponding to the nonconservation of the particle number
operator in the quantum field theory, the theory describes explicit creation
and annihilation events: the world lines for the particles can begin and end.Comment: 4 pages, uses RevTeX4, 2 figures; v2: shortened and with minor
addition
Seven Steps Towards the Classical World
Classical physics is about real objects, like apples falling from trees,
whose motion is governed by Newtonian laws. In standard Quantum Mechanics only
the wave function or the results of measurements exist, and to answer the
question of how the classical world can be part of the quantum world is a
rather formidable task. However, this is not the case for Bohmian mechanics,
which, like classical mechanics, is a theory about real objects. In Bohmian
terms, the problem of the classical limit becomes very simple: when do the
Bohmian trajectories look Newtonian?Comment: 16 pages, LaTeX, uses latexsy
Are All Particles Identical?
We consider the possibility that all particles in the world are fundamentally
identical, i.e., belong to the same species. Different masses, charges, spins,
flavors, or colors then merely correspond to different quantum states of the
same particle, just as spin-up and spin-down do. The implications of this
viewpoint can be best appreciated within Bohmian mechanics, a precise
formulation of quantum mechanics with particle trajectories. The implementation
of this viewpoint in such a theory leads to trajectories different from those
of the usual formulation, and thus to a version of Bohmian mechanics that is
inequivalent to, though arguably empirically indistinguishable from, the usual
one. The mathematical core of this viewpoint is however rather independent of
the detailed dynamical scheme Bohmian mechanics provides, and it amounts to the
assertion that the configuration space for N particles, even N
``distinguishable particles,'' is the set of all N-point subsets of physical
3-space.Comment: 12 pages LaTeX, no figure
On the quantum probability flux through surfaces
We remark that the often ignored quantum probability current is fundamental
for a genuine understanding of scattering phenomena and, in particular, for the
statistics of the time and position of the first exit of a quantum particle
from a given region, which may be simply expressed in terms of the current.
This simple formula for these statistics does not appear as such in the
literature. It is proposed that the formula, which is very different from the
usual quantum mechanical measurement formulas, be verified experimentally. A
full understanding of the quantum current and the associated formula is
provided by Bohmian mechanics.Comment: 15 pages, 3 figures, revised and more detailed version, to be
published in Journal of Statistical Physics, August 9
Trajectories and Particle Creation and Annihilation in Quantum Field Theory
We develop a theory based on Bohmian mechanics in which particle world lines
can begin and end. Such a theory provides a realist description of creation and
annihilation events and thus a further step towards a "beable-based"
formulation of quantum field theory, as opposed to the usual "observable-based"
formulation which is plagued by the conceptual difficulties--like the
measurement problem--of quantum mechanics.Comment: 11 pages LaTeX, no figures; v2: references added and update
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
Development of optimum clamp combinations for strap-down inertial measuring units with field replaceable sensors
Optimum clamp combinations for strap down inertial measuring units with field replaceable sensor
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