108 research outputs found
Network Cosmology
Prediction and control of the dynamics of complex networks is a central
problem in network science. Structural and dynamical similarities of different
real networks suggest that some universal laws might accurately describe the
dynamics of these networks, albeit the nature and common origin of such laws
remain elusive. Here we show that the causal network representing the
large-scale structure of spacetime in our accelerating universe is a power-law
graph with strong clustering, similar to many complex networks such as the
Internet, social, or biological networks. We prove that this structural
similarity is a consequence of the asymptotic equivalence between the
large-scale growth dynamics of complex networks and causal networks. This
equivalence suggests that unexpectedly similar laws govern the dynamics of
complex networks and spacetime in the universe, with implications to network
science and cosmology
Empirical Foundation of Space and Time
I will sketch a possible way of empirical/operational definition of space and time tags of physical events, without logical or operational circularities and with a minimal number of conventional elements. As it turns out, the task is not trivial; and the analysis of the problem leads to a few surprising conclusions
Revisiting special relativity: A natural algebraic alternative to Minkowski spacetime
Minkowski famously introduced the concept of a space-time continuum in 1908,
merging the three dimensions of space with an imaginary time dimension , with the unit imaginary producing the correct spacetime distance , and the results of Einstein's then recently developed theory of special
relativity, thus providing an explanation for Einstein's theory in terms of the
structure of space and time. As an alternative to a planar Minkowski space-time
of two space dimensions and one time dimension, we replace the unit imaginary , with the Clifford bivector for the plane
that also squares to minus one, but which can be included without the addition
of an extra dimension, as it is an integral part of the real Cartesian plane
with the orthonormal basis and . We find that with this model of
planar spacetime, using a two-dimensional Clifford multivector, the spacetime
metric and the Lorentz transformations follow immediately as properties of the
algebra. This also leads to momentum and energy being represented as components
of a multivector and we give a new efficient derivation of Compton's scattering
formula, and a simple formulation of Dirac's and Maxwell's equations. Based on
the mathematical structure of the multivector, we produce a semi-classical
model of massive particles, which can then be viewed as the origin of the
Minkowski spacetime structure and thus a deeper explanation for relativistic
effects. We also find a new perspective on the nature of time, which is now
given a precise mathematical definition as the bivector of the plane.Comment: 29 pages, 2 figure
The emergence of reciprocally beneficial cooperation
We offer a new and robust model of the emergence and persistence of cooperation when interactions are anonymous, the population is well-mixed, and evolution selects strategies according to material payoffs. The model has a Prisoner’s Dilemma structure, but with an outside option of non-participation. The payoff to mutual cooperation is stochastic; with positive probability, it exceeds that from cheating against a cooperator. Under mild conditions, mutually beneficial cooperation occurs in equilibrium. This is possible because the non-participation option holds down the equilibrium frequency of cheating. Dynamic properties of the model are investigated theoretically and through simulations based on replicator dynamics
Cooperation, Norms, and Revolutions: A Unified Game-Theoretical Approach
Cooperation is of utmost importance to society as a whole, but is often
challenged by individual self-interests. While game theory has studied this
problem extensively, there is little work on interactions within and across
groups with different preferences or beliefs. Yet, people from different social
or cultural backgrounds often meet and interact. This can yield conflict, since
behavior that is considered cooperative by one population might be perceived as
non-cooperative from the viewpoint of another.
To understand the dynamics and outcome of the competitive interactions within
and between groups, we study game-dynamical replicator equations for multiple
populations with incompatible interests and different power (be this due to
different population sizes, material resources, social capital, or other
factors). These equations allow us to address various important questions: For
example, can cooperation in the prisoner's dilemma be promoted, when two
interacting groups have different preferences? Under what conditions can costly
punishment, or other mechanisms, foster the evolution of norms? When does
cooperation fail, leading to antagonistic behavior, conflict, or even
revolutions? And what incentives are needed to reach peaceful agreements
between groups with conflicting interests?
Our detailed quantitative analysis reveals a large variety of interesting
results, which are relevant for society, law and economics, and have
implications for the evolution of language and culture as well
On the expected number of internal equilibria in random evolutionary games with correlated payoff matrix
The analysis of equilibrium points in random games has been of great interest
in evolutionary game theory, with important implications for understanding of
complexity in a dynamical system, such as its behavioural, cultural or
biological diversity. The analysis so far has focused on random games of
independent payoff entries. In this paper, we overcome this restrictive
assumption by considering multi-player two-strategy evolutionary games where
the payoff matrix entries are correlated random variables. Using techniques
from the random polynomial theory we establish a closed formula for the mean
numbers of internal (stable) equilibria. We then characterise the asymptotic
behaviour of this important quantity for large group sizes and study the effect
of the correlation. Our results show that decreasing the correlation among
payoffs (namely, of a strategist for different group compositions) leads to
larger mean numbers of (stable) equilibrium points, suggesting that the system
or population behavioural diversity can be promoted by increasing independence
of the payoff entries. Numerical results are provided to support the obtained
analytical results.Comment: Revision from the previous version; 27 page
Evolutionary Substitution and Replacement in N-Species Lotka-Volterra Systems
The successful invasion of a multi-species resident system by mutants has received a great deal of attention in theoretical
ecology but less is known about what happens after the successful invasion. Here, in the framework of Lotka-Volterra (LV) systems, we
consider the general question where there is one resident phenotype in
each species and the evolutionary outcome after invasion remains one
phenotype in each species but these include all the mutant phenotypes. In the first case, called evolutionary substitution, a mutant appears
in only one species, the resident phenotype in this species dies out and
the mutant coexists with the original phenotypes of the other species.
In the second case, called evolutionary replacement, a mutant appears
in each species, all resident phenotypes die out and the evolutionary
outcome is coexistence among all the mutant phenotypes. For general
LV systems, we show that dominance of the resident phenotype by
the mutant (i.e. the mutant is always more fit) in each species where
the mutant appears leads to evolutionary substitution/replacement.
However, it is shown by example that, when dominance is weakened
to only assuming the average fitness of the mutants is greater than
the average for the resident phenotype, the residents may not die out.
We also show evolutionary substitution occurs in two-species competitive LV systems when the initial invasion of the resident system
(respectively, of the new coexistence system) is successful (respectively, unsuccessful). Moreover, if sequential evolutionary substitution
occurs for either order that the two mutant phenotypes appear (called
historically independent replacement), then it is shown evolutionar
Descriptive Topological Spaces for Performing Visual Search
Accepted versionThis article presents an approach to performing the task of visual search in the context of descriptive topological spaces. The presented algorithm forms the basis of a descriptive visual search system (DVSS) that is based on the guided search model (GSM) that is motivated by human visual search. This model, in turn, consists of the bottom-up and top-down attention models and is implemented within the DVSS in three distinct stages. First, the bottom-up activation process is used to generate saliency maps and to identify salient objects. Second, perceptual objects, defined in the context of descriptive topological spaces, are identified and associated with feature vectors obtained from a VGG deep learning convolutional neural network. Lastly, the top-down activation process makes decisions on whether the object of interest is present in a given image through the use of descriptive patterns within the context of a descriptive topological space. The presented approach is tested with images from the ImageNet ILSVRC2012 and SIMPLIcity datasets. The contribution of this article is a descriptive pattern-based visual search algorithm."This research has been supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant 418413, and the Faculty of Graduate
Studies at the University of Winnipeg."https://link.springer.com/chapter/10.1007/978-3-662-58768-3_
- …