2,754 research outputs found
Strange nonchaotic stars
The unprecedented light curves of the Kepler space telescope document how the
brightness of some stars pulsates at primary and secondary frequencies whose
ratios are near the golden mean, the most irrational number. A nonlinear
dynamical system driven by an irrational ratio of frequencies generically
exhibits a strange but nonchaotic attractor. For Kepler's "golden" stars, we
present evidence of the first observation of strange nonchaotic dynamics in
nature outside the laboratory. This discovery could aid the classification and
detailed modeling of variable stars.Comment: 5 pages, 4 figures, published in Physical Review Letter
Coupling Reduces Noise
We demonstrate how coupling nonlinear dynamical systems can reduce the
effects of noise. For simplicity we investigate noisy coupled map lattices.
Noise from different lattice nodes can diffuse across the lattice and lower the
noise level of individual nodes. We develop a theoretical model that explains
this observed noise evolution and show how the coupled dynamics can naturally
function as an averaging filter. Our numerical simulations are in excellent
agreement with the model predictions
Quantum gravity on a laptop: 1+1 Dimensional Causal Dynamical Triangulation simulation
AbstractThe quest for quantum gravity has been long and difficult. Causal Dynamical Triangulation is a new and straightforward approach to quantum gravity that recovers classical spacetime at large scales by enforcing causality at small scales. CDT combines quantum physics with general relativity in a Feynman sum-over-geometries and converts the sum into a discrete statistical physics problem. We solve this problem using a new Monte Carlo simulation to compute the spatial fluctuations of an empty universe with one space and one time dimensions. Our results compare favorably with theory and provide an accessible but detailed introduction to quantum gravity via a simulation that runs on a laptop computer
Pulsation period variations in the RRc Lyrae star KIC 5520878
Learned et. al. proposed that a sufficiently advanced extra-terrestrial
civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino
beam at the right time, thus causing them to trigger early and jogging the
otherwise very regular phase of their expansion and contraction. This would
turn these stars into beacons to transmit information throughout the galaxy and
beyond. The idea is to search for signs of phase modulation (in the regime of
short pulse duration) and patterns, which could be indicative of intentional,
omnidirectional signaling.
We have performed such a search among variable stars using photometric data
from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have
found two such regimes of long and short pulse durations. The sequence of
period lengths, expressed as time series data, is strongly auto correlated,
with correlation coefficients of prime numbers being significantly higher
(\%). Our analysis of this candidate star shows that the prime number
oddity originates from two simultaneous pulsation periods and is likely of
natural origin.
Simple physical models elucidate the frequency content and asymmetries of the
KIC 5520878 light curve.
Despite this SETI null result, we encourage testing other archival and future
time-series photometry for signs of modulated stars. This can be done as a
by-product to the standard analysis, and even partly automated.Comment: Accepted for publication in ApJ. 49 pages, 16 figure
Simple nonlinear models suggest variable star universality
Dramatically improved data from observatories like the CoRoT and Kepler
spacecraft have recently facilitated nonlinear time series analysis and
phenomenological modeling of variable stars, including the search for strange
(aka fractal) or chaotic dynamics. We recently argued [Lindner et al., Phys.
Rev. Lett. 114 (2015) 054101] that the Kepler data includes "golden" stars,
whose luminosities vary quasiperiodically with two frequencies nearly in the
golden ratio, and whose secondary frequencies exhibit power-law scaling with
exponent near -1.5, suggesting strange nonchaotic dynamics and singular
spectra. Here we use a series of phenomenological models to make plausible the
connection between golden stars and fractal spectra. We thereby suggest that at
least some features of variable star dynamics reflect universal nonlinear
phenomena common to even simple systems.Comment: 9 pages, 9 figures, accepted for publication in Physica
Neural networks embrace learned diversity
Diversity conveys advantages in nature, yet homogeneous neurons typically
comprise the layers of artificial neural networks. Here we construct neural
networks from neurons that learn their own activation functions, quickly
diversify, and subsequently outperform their homogeneous counterparts.
Sub-networks instantiate the neurons, which meta-learn especially efficient
sets of nonlinear responses. Such learned diversity provides examples of
dynamical systems selecting diversity over uniformity and elucidates the role
of diversity in natural and artificial systems.Comment: 6 pages, 6 figure
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