22,588 research outputs found
Back to Parmenides
After a brief introduction to issues that plague the realization of a theory
of quantum gravity, I suggest that the main one concerns a quantization of the
principle of relative simultaneity. This leads me to a distinction between time
and space, to a further degree than that present in the canonical approach to
general relativity. With this distinction, one can make sense of superpositions
as interference between alternative paths in the relational configuration space
of the entire Universe. But the full use of relationalism brings us to a
timeless picture of Nature, as it does in the canonical approach (which
culminates in the Wheeler-DeWitt equation). After a discussion of Parmenides
and the Eleatics' rejection of time, I show that there is middle ground between
their view of absolute timelessness and a view of physics taking place in
timeless configuration space. In this middle ground, even though change does
not fundamentally exist, the illusion of change can be recovered in a way not
permitted by Parmenides. It is recovered through a particular density
distribution over configuration space which gives rise to 'records'.
Incidentally, this distribution seems to have the potential to dissolve further
aspects of the measurement problem that can still be argued to haunt the
application of decoherence to Many-Worlds quantum mechanics. I end with a
discussion indicating that the conflict between the conclusions of this paper
and our view of the continuity of the self may still intuitively bother us.
Nonetheless, those conclusions should be no more challenging to our intuition
than Derek Parfit's thought experiments on the subject.Comment: 25 pages, 1 figure. Winner of the essay contest: "Space-time after
quantum gravity" (University of Illinois and Universit\'e de Geneve). To be
published in special editio
Model inspired by population genetics to study fragmentation of brittle plates
We use a model whose rules were inspired by population genetics, the random
capability growth model, to describe the statistical details observed in
experiments of fragmentation of brittle platelike objects, and in particular
the existence of (i) composite scaling laws, (ii) small critical exponents \tau
associated with the power-law fragment-size distribution, and (iii) the typical
pattern of cracks. The proposed computer simulations do not require numerical
solutions of the Newton's equations of motion, nor several additional
assumptions normally used in discrete element models. The model is also able to
predict some physical aspects which could be tested in new experiments of
fragmentation of brittle systems.Comment: We have modified the text in order to make the description of the
model more clear. One Figure (Figure 1) was introduced showing the steps of
the dynamics of colonization. Twelve references were adde
Plastic Deformation of 2D Crumpled Wires
When a single long piece of elastic wire is injected trough channels into a
confining two-dimensional cavity, a complex structure of hierarchical loops is
formed. In the limit of maximum packing density, these structures are described
by several scaling laws. In this paper it is investigated this packing process
but using plastic wires which give origin to completely irreversible structures
of different morphology. In particular, it is studied experimentally the
plastic deformation from circular to oblate configurations of crumpled wires,
obtained by the application of an axial strain. Among other things, it is shown
that in spite of plasticity, irreversibility, and very large deformations,
scaling is still observed.Comment: 5 pages, 6 figure
Evading the Few TeV Perturbative Limit in 3-3-1 Models
Some versions of the electroweak SU(3)_L\otimesU(1)_X models cannot be
treated within perturbation theory at energies of few TeV. An extended version
for these models is proposed which is perturbative even at TeV scale posing no
threatening inconsistency for test at future colliders. The extension presented
here needs the addition of three octets of vector leptons, which leave three
new leptonic isotriplets in the SU(2)_L\otimesU(1)_Y subgroup. With this
representation content the running of the electroweak mixing angle, , is such that decreases with the increase of the
energy scale , when only the light states of the Standard Model group are
considered. The neutral exotic gauge boson marks then a new symmetry
frontier.Comment: 15 pages, 2 figures, minor correction
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