arXiv subjects

Serge Galam

Publications and source records attributed to Serge Galam.

At least 73 records · Page 4Linked to original sources

arXiv2007

Stability of leadership in bottom-up hierarchical organizations

The stability of a leadership against a growing internal opposition is studied in bottom-up hierarchical organizations. Using a very simple model with bottom-up majority rule voting, the dynamics of power distribution at the various hierarchical levels is calculated within a probabilistic framework. Given a leadership at the top, the opposition weight from the hierarchy bottom is shown to fall off quickly while climbing up the hierarchy. It reaches zero after only a few hierarchical levels. Indeed the voting process is found to obey a threshold dynamics with a deterministic top outcome. Accordingly the leadership may stay stable against very large amplitude increases in the opposition at the bottom level. An opposition can thus grow steadily from few percent up to seventy seven percent with not one a single change at the elected top level. However and in contrast, from one election to another, in the vicinity of the threshold, less than a one percent additional shift at the bottom level can drive a drastic and brutal change at the top. The opposition topples the current leadership at once. In addition to analytical formulas, results from a large scale simulation are presented. The results may shed a new light on management architectures as well as on alert systems. They could also provide some different insight on last century's Eastern European communist collapse.

physics.soc-ph↗

arXiv2007

The role of inflexible minorities in the breaking of democratic opinion dynamics

We study the effect of inflexible agents on two state opinion dynamics. The model operates via repeated local updates of random grouping of agents. While floater agents do eventually flip their opinion to follow the local majority, inflexible agents keep their opinion always unchanged. It is a quenched individual opinion. In the bare model (no inflexibles), a separator at 50% drives the dynamics towards either one of two pure attractors, each associated with a full polarization along one of the opinions. The initial majority wins. The existence of inflexibles for only one of the two opinions is found to shift the separator at a lower value than 50% in favor of that side. Moreover it creates an incompressible minority around the inflexibles, one of the pure attractors becoming a mixed phase attractor. In addition above a threshold of 17% inflexibles make their side sure of winning whatever the initial conditions are. The inflexible minority wins. An equal presence of inflexibles on both sides restores the balanced dynamics with again a separator at 50% and now two mixed phase attractors on each side. Nevertheless, beyond 25% the dynamics is reversed with a unique attractor at a fifty-fifty stable equilibrium. But a very small advantage in inflexibles results in a decisive lowering of the separator at the advantage of the corresponding opinion. A few percent advantage does guarantee to become majority with one single attractor. The model is solved exhaustedly for groups of size 3.

physics.soc-ph↗

arXiv2006

Chaotic, staggered and polarized dynamics in opinion forming: the contrarian effect

We revisit the no tie breaking 2-state Galam contrarian model of opinion dynamics for update groups of size 3. While the initial model assumes a constant density of contrarians a for both opinions, it now depends for each opinion on its global support. Proportionate contrarians are thus found to indeed preserve the former case main results. However, restricting the contrarian behavior to only the current collective majority, makes the dynamics more complex with novel features. For a density a 0.301 the chaotic basin disappears and the majority starts to alternate between the two opinions with a staggered flow towards two point attractors. We then study the effect of both, decoupling the local update time sequence from the contrarian behavior activation, and a smoothing of the majority rule. A status quo driven bias for contrarian activation is also considered. Introduction of unsettled agents driven in the debate on a contrarian basis is shown to only shrink the chaotic basin. The model may shed light to recent apparent contradictory elections with on the one hand very tied results like in US in 2000 and in Germany in 2002 and 2005, and on the other hand, a huge majority like in France in 2002.

physics.soc-ph↗

arXiv2004

Heterogeneous believes, segregation and extremism in the making of public opinions

The connection between contradictory public opinions, heterogeneous believes and the emergence of democratic or dictatorial extremism is studied extending our former two state dynamic opinion model. Agents are attached to a social-cultural class. At each step they are distributed randomly in different groups within their respective class to evolve locally by majority rule. In case of a tie the group adopts either one opinion with respective probabilities k and (1-k). The value of k accounts for the average of individual biases driven by the existence of heterogeneous believes within the corresponding class. It may vary from class to class. The process leads to extremism with a full polarization of each class along either one opinions. For homogeneous classes the extremism can be along the initial minority making it dictatorial. At contrast heterogeneous classes exhibit a more balanced dynamics which results in a democratic extremism. Segregation among subclasses may produce a coexistence of opinions at the class level thus averting global extremism. The existence of contradictory public opinions in similar social-cultural neighborhoods is given a new light.

cond-mat.other↗

arXiv2004

Fashion, Novelty and Optimality: An application from Physics

We apply a physical based model to describe the clothes fashion market. Every time a new outlet appears on the market, it can invade the market under certain specific conditions. Hence, the "old'' outlet can be completely dominated and disappears. Each creator competes for a finite population of agents. Fashion phenomena are shown to result from a collective phenomenon produced by local individual imitation effects. We assume that, in each step of the imitation process, agents only interact with a subset rather than with the whole set of agents. People are actually more likely to influence (and be influenced by) their close ''neighbours''. Accordingly we discuss which strategy is best fitted for new producers when people are either simply organised into anonymous reference groups or when they are organised in social groups hierarchically ordered. While counterfeits are shown to reinforce the first strategy, creating social leaders can permit to avoid them.

cond-mat.other↗

arXiv2004

Unifying Local Dynamics in Two-State Spin Systems

We present a new two-state {+-} opinion dynamics model which defines a general frame to include all local dynamics in two-state spin systems. Agents evolve by probabilistic local rules. In each update, groups of various sizes k are formed according to some probability distribution {a_k}. Given a specific group with an initial (j) agents sharing opinion {+} and (k-j) agents opinion {-}, all k members adopt opinion {+} with a probability m_{k,j} and opinion {-} with (1-m_{k,j}). A very rich and new spectrum of dynamics is obtained. The final opinion is a polarization along the initial majority, along the initial minority or a perfect consensus with an equality of opinions as function of the parameters {a_k, m_{k,j}}. In last case, two regimes exist, monotonic and dampened oscillatory. The transition from polarization to consensus dynamics occurs for values of the parameters which reproduce exactly the Voter model. A scheme is presented to express any local update in terms of a specific set {a_k, m_{k,j}}. Most existing opinion models are exhibited at particular limits.

cond-mat.dis-nn↗

arXiv2004

Restoring site percolation on a damaged square lattice

We study how to restore site percolation on a damaged square lattice with nearest neighbor (N$^2$) interactions. Two strategies are suggested for a density $x$ of destroyed sites by a random attack at $p_c$. In the first one, a density $y$ of new sites are created with longer range interactions, either next nearest neighbor (N$^3$) or next next nearest neighbor (N$^4$). In the second one, new longer range interactions N$^3$ or N$^4$ are created for a fraction $v$ of the remaining $(p_c-x)$ sites in addition to their N$^2$ interactions. In both cases, the values of $y$ and $v$ are tuned in order to restore site percolation which then occurs at new percolation thresholds, respectively $π_3$, $π_4$, $π_{23}$ and $π_{24}$. Using Monte Carlo simulations the values of the pairs $\{y, π_3 \}$, $\{y, π_4\}$ and $\{v, π_{23}\}$, $\{v, π_{24}\}$ are calculated for the whole range $0\leq x \leq p_c(\text{N}^2)$. Our schemes are applicable to all regular lattices.

cond-mat.stat-mech↗

arXiv2004

Global Physics: From Percolation to Terrorism, Guerilla Warfare and Clandestine Activities

The September 11 attack on the US has revealed an unprecedented terrorism with worldwide range of destruction. It is argued to result from the first worldwide percolation of passive supporters. They are people sympathetic to the terrorism cause but without being involved with it. They just don't oppose it in case they could. This scheme puts suppression of the percolation as the major strategic issue in the fight against terrorism. Acting on the population is shown to be useless. Instead a new strategic scheme is suggested to increase the terrorism percolation threshold and in turn suppress the percolation. The relevant associated space is identified as a multi-dimensional social space including both the ground earth surface and all various independent flags displayed by the terrorist group. Some hints are given on how to shrink the geographical spreading of terrorism threat. The model apply to a large spectrum of clandestine activities including guerilla warfare as well as tax evasion, corruption, illegal gambling, illegal prostitution and black markets.

cond-mat.dis-nn↗

arXiv2004

Sociophysics: a personal testimony

The origins of Sociophysics are discussed from a personal testimony. I trace back its history to the late seventies. My twenty years of activities and research to establish and promote the field are reviewed. In particular the conflicting nature of Sociophysics with the physics community is revealed from my own experience. Recent presentations of a supposed natural growth from Social Sciences are criticized.

physics.soc-ph↗

arXiv2003

Contrarian Deterministic Effect: the "Hung Elections Scenario"

A contrarian is someone who deliberately decides to oppoe the prevailing choice of others. The Galam model of two state opinion dynamicsincorporates agent updates by a single step random grouping in which all participants adopt the opinion of their respective local majority group. The process is repeated until a stable collective state is reached; the associated dynamics is fast. Here we show that the introduction of contrarians may give rise to interesting dynamics generated phases and even to a critical behavior at a contrarian concentration $a_c$. For $a a_c$ the resulting disordered phase has no majority: agents keep shifting opinions but no symmetry breaking (i.e., the appearance of a majority) takes place. Our results are employed to explain the outcome of the 2000 American presidential elections and that of the 2002 German parliamentary elections. Those events are found to be inevitable. On this basis the ``hung elections scenario'' is predicted to become a common occurrence in modern democracies.

cond-mat.stat-mech↗

arXiv2003

On reducing Terrorism Power: A Hint from Physics

The September 11 attack on the US has revealed an unprecedented terrorism worldwide range of destruction. Recently, it has been related to the percolation of worldwide spread passive supporters. This scheme puts the suppression of the percolation effect as the major strategic issue in the fight against terrorism. Accordingly the world density of passive supporters should be reduced below the percolation threshold. In terms of solid policy, it means to neutralize millions of random passive supporters, which is contrary to ethics and out of any sound practical scheme. Given this impossibility we suggest instead a new strategic scheme to act directly on the value of the terrorism percolation threshold itself without harming the passive supporters. Accordingly we identify the space hosting the percolation phenomenon to be a multi-dimensional virtual social space which extends the ground earth surface to include the various independent terrorist-fighting goals. The associated percolating cluster is then found to create long-range ground connections to terrorism activity. We are thus able to modify the percolation threshold pc in the virtual space to reach p<pc by decreasing the social space dimension, leaving the density p unchanged. At once that would break down the associated world terrorism network to a family of unconnected finite size clusters. The current world terrorism threat would thus shrink immediately and spontaneously to a local geographic problem. There, military action would become limited and efficient.

cond-mat.dis-nn↗

arXiv2002

Spontaneous coalition forming: Why some are stable?

A model to describe the spontaneous formation of military and economic coalitions among a group of countries is proposed using spin glass theory. Between each couple of countries, there exists a bond exchange coupling which is either zero, cooperative or conflicting. It depends on their common history, specific nature, and cannot be varied. Then, given a frozen random bond distribution, coalitions are found to spontaneously form. However they are also unstable making the system very disordered. Countries shift coalitions all the time. Only the setting of macro extra national coalition are shown to stabilize alliances among countries. The model gives new light on the recent instabilities produced in Eastern Europe by the Warsow pact dissolution at odd to the previous communist stability. Current European stability is also discussed with respect to the European Union construction.

cond-mat.dis-nn↗

arXiv2002

Modeling Rumors: The No Plane Pentagon French Hoax Case

The recent astonishing wide adhesion of french people to the rumor claiming `No plane did crash on the Pentagon on September the 11", is given a generic explanation in terms of a model of minority opinion spreading. Using a majority rule reaction-diffusion dynamics, a rumor is shown to invade for sure a social group provided it fulfills simultaneously two criteria. First it must initiate with a support beyond some critical threshold which however, turns out to be always very low. Then it has to be consistent with some larger collective social paradigm of the group. Othewise it just dies out. Both conditions were satisfied in the french case with the associated book sold at more than 200 000 copies in just a few days. The rumor was stopped by the firm stand of most newspaper editors stating it is nonsense. Such an incredible social dynamics is shown to result naturally from an open and free public debate among friends and colleagues. Each one searching for the truth sincerely on a free will basis and without individual biases. The polarization process appears also to be very quick in agreement with reality. It is a very strong anti-democratic reversal of opinion although made quite democratically. The model may apply to a large range of rumors.

cond-mat.dis-nn↗

arXiv2002

Solving the Triangular Ising Antiferromagnet by Simple Mean Field

Few years ago, application of the mean field Bethe scheme on a given system was shown to produce a systematic change of the system intrinsic symmetry. For instance, once applied on a ferromagnet, individual spins are no more equivalent. Accordingly a new loopwise mean field theory was designed to both go beyond the one site Weiss approach and yet preserve the initial Hamitonian symmetry. This loopwise scheme is applied here to solve the Triangular Antiferromagnetic Ising model. It is found to yield Wannier's exact result of no ordering at non-zero temperature. No adjustable parameter is used. Simultaneously a non-zero critical temperature is obtained for the Triangular Ising Ferromagnet. This simple mean field scheme opens a new way to tackle random systems.

cond-mat.dis-nn↗

arXiv2002

A 1-d Ising model for ripple formation

A 1-d Ising model is shown to reproduce qualitatively the dynamics of ripple formation. Saltation effect is imposed using a Kawasaki dynamics and a pair interaction over some distance l. Within this model, the ripple state turns out to be metastable in agreement with cellular automata simulations as well as recent under water experiments. A dynamical phase diagram is obtained. A mean-field solution of the problem is given in terms of the ripple size. A mapping is then performed onto a 2-dimensional l x infinity static problem.

cond-mat.dis-nn↗

arXiv2002

Killer Geometries in Competing Species Dynamics

We discuss a cellular automata model to study the competition between an emergent better fitted species against an existing majority species. The model implement local fights among small group of individual and a synchronous random walk on a 2D lattice. The faith of the system, i.e. the spreading or disappearance of the species is determined by their initial density and fight frequency. The initial density of the emergent species has to be higher than a critical threshold for total spreading but this value depends in a non-trivial way of the fight frequency. Below the threshold any better adapted species disappears showing that a qualitative advantage is not enough for a minority to win. No strategy is involved but spatial organization turns out to be crucial. For instance at minority densities of zero measure some very rare local geometries which occur by chance are found to be killer geometries. Once set they lead with high probability to the total destruction of the preexisting majority species. The occurrence rate of these killer geometries is function of the system size. This model may apply to a large spectrum of competing groups like smoker-non smoker, opinion forming, diffusion of innovation setting of industrial standards, species evolution, epidemic spreading and cancer growth.

cond-mat.dis-nn↗

arXiv2002

The September 11 Attack: A Percolation of Individual Passive Support

A model for terrorism is presented using the theory of percolation. Terrorism power is related to the spontaneous formation of random backbones of people who are sympathetic to terrorism but without being directly involved in it. They just don't oppose in case they could. In the past such friendly-to-terrorism backbones have been always existing but were of finite size and localized to a given geographical area. The September 11 terrorist attack on the US has revealed for the first time the existence of a world wide spread extension. It is argued to have result from a sudden world percolation of otherwise unconnected and dormant world spread backbones of passive supporters. The associated strategic question is then to determine if collecting ground information could have predict and thus avoid such a transition. Our results show the answer is no, voiding the major criticism against intelligence services. To conclude the impact of military action is discussed.

cond-mat.dis-nn↗

arXiv2002

Minority Opinion Spreading in Random Geometry

The dynamics of spreading of the minority opinion in public debates (a reform proposal, a behavior change, a military retaliation) is studied using a diffusion reaction model. People move by discrete step on a landscape of random geometry shaped by social life (offices, houses, bars, and restaurants). A perfect world is considered with no advantage to the minority. A one person-one argument principle is applied to determine locally individual mind changes. In case of equality, a collective doubt is evoked which in turn favors the Status Quo.Starting from a large in favor of the proposal initial majority, repeated random size local discussions are found to drive the majority reversal along the minority hostile view. Total opinion refusal is completed within few days. Recent national collective issues are revisited. The model may apply to rumor and fear propagation.

cond-mat.dis-nn↗