Tipping Points in Opinion Dynamics: A Universal Formula in Five Dimensions

A universal formula is shown to predict the dynamics of public opinion including eventual sudden and unexpected outbreaks of minority opinions within a generic parameter space of five dimensions. The formula is obtained by combining and extending several components of the Galam model of opinion dynamics, otherwise treated separately, into one single update equation, which then deploys in a social space of five dimensions. Four dimensions account for a rich diversity of individual traits within a heterogeneous population, including differentiated stubbornness, contrarianism, and embedded prejudices. The fifth dimension is the size of the update groups being discussed. Having one single formula allows one to explore the complete geometry of the underlying landscape of opinion dynamics. Attractors and tipping points, which shape the topology of the different possible dynamics flows, are unveiled. Driven by repeated discussion among small groups of people during a social or political public campaign, the phenomenon of minority spreading and parallel majority collapse are thus revealed ahead of their occurrence. Accordingly, within the opinion landscape, unexpected and sudden events such as Brexit and Trump victories become visible within a forecast time horizon, making them predictable. Despite the accidental nature of the landscape, evaluating the parameter values for a specific case allows one to single out which basin of attraction is going to drive the associate dynamics, and thus, a prediction of the outcome becomes feasible. The model may apply to a large spectrum of social situations including voting outcomes, market shares, and societal trends, allowing us to envision novel winning strategies in competing environments.


INTRODUCTION
Majoritarian social decisions have been traditionally justified by Condorcet's jury theorem which states that, in majoritarian group decisions, the errors in individual judgment are canceled out to arbitrary accuracy as the number of voters increases. This implies the stable dominance of rational majority in democratic decision-making. In reality, however, democratic majoritarianism can produce seemingly unexpected sudden shifts, as exemplified by political events such as the 2016 Brexit victory and Trump election. There is also a glaring contradiction in democracy in which there exist powerful interest groups that exert disproportionate power despite their minority status.
Such unexpected and paradoxical outcomes of opinion dynamics are challenging puzzles, which are yet to be elucidated. In particular, with public opinion being nowadays a major key to trigger eventual changes in modern societies as well as collapses of political regimes, the understanding of the mechanisms behind the making of public opinion becomes a major issue of vital interest.
It happened that from the beginning of sociophysics [1], the study of opinion dynamics has been a main topic of research, which has shed new and disruptive light about these paradoxical features resulting from majority group decision [2][3][4][5][6]. A great deal of models have been, and are yet to be, proposed to describe opinion dynamics in social systems [7][8][9][10][11][12]. Most of them consider homogeneous populations with a local update rule and discrete variables. A series of these models were shown to be included within a single unifying frame [13]. Continuous variables have also been used [14,15]. Yet, despite ongoing active research [16][17][18][19][20][21] up-to-date, the opinion dynamics issue is still lacking a comprehensive and robust framework, especially a reliable predictive tool.
In this work, by investigating further the Galam model in a generic parameter space of five dimensions, we obtain a single universal update equation to follow the temporal evolution of opinion distribution among a heterogeneous population with any combination of rational, stubborn, and contrarian agents for any average of hidden prejudices and for an arbitrary size of groups being discussed.
The update equation allows one to explore the complete geometry of the underlying landscape. In particular, attractors and tipping points which shape the faith of possible dynamics flows are unveiled. The underlying dynamics path of public opinion driven by repeated discussion among small groups of people during a social or political public campaign becomes predictable. Future occurrence of sudden minority spreading and parallel majority collapse ahead of their actual occurrence is revealed as shown with 2016 Brexit and Trump victories. They became visible within a forecast time horizon and in turn predictable.
In addition, having the full five-dimensional landscape makes predictions more feasible and robust because, then, the precise evaluation of the parameter values is not required. Instead, what matters is identifying the relevant basin of attraction where the dynamics will take place. However, along the basin boundaries, more-precise estimates of the parameters are necessary.
Having a universal formula which accounts for generic psychological features makes the model applicable to a large spectrum of social situations including voting outcomes, market shares, and societal trends. The results also allow us to envision novel winning strategies in competing environments to win a public debate or a market share.
The rest of the article is organized as follows. In Section 2, we outline the derivation of the universal formula aggregating the various components of the Galam model. A few illustrations of sudden and unexpected minority outbreaks yielded by the equation are exhibited in Section 3. Section 4 contains some explicit expressions for the evolution equation for (some) few specific values of the group size r. We analyze the mathematical structure of the universal update equation through the identification of its fixed points in Section 5. Section 6 explores some aspects of the five-dimensional parameter space of the model pointing out the existence of critical points. The results are illustrated with several numerical examples. Concluding remarks are presented in the last section.

THE UNIVERSAL FORMULA IN FIVE-DIMENSIONAL PARAMETER SPACE
We consider a population with N agents, each capable of taking two states 1 and 0, respectively, representing two exclusive opinions A and B. At a given time t, the corresponding proportions of agents holding A and B are denoted as p t and (1 − p t ). To make legitimate use of proportions and probabilities, we focus on cases with N > 100 [26]. Choosing an initial time t 0, we investigate the time evolution of p 0 driven by informal local discussion among agents at successive discrete time steps with p 0 → p 1 → p 2 → . . .
To account for this complicated and unknown process, we use the Galam dynamical model, which monitors the opinion dynamics by a sequential iterated scheme. To implement one scheme, agents are first randomly distributed within small groups of size r. Then, within each group, a majority rule is applied to update local agent opinions. Each agent has one vote to determine the actual local majority. However, to account for the heterogeneity of psychological traits among agents, not all of them obey the majority rule by shifting the opinion if holding the local minority choice. Three types of agents, floaters, inflexibles, and contrarians, are considered. After local updates are performed, all groups are dismantled and agents are reshuffled, thus erasing the local correlations which were created by applying the local majority rules.
• The floaters vote to determine the local majority and, afterward, the ones holding the minority opinion shift to adopt the majority opinion. However, in case of a tie in a local even-size group, floaters adopt the choice in tune with the leading prejudice among the group members [3]. This prejudice-driven tie breaking is activated unconsciously by the agents. Accordingly, at a tie, opinion A is chosen with probability k and opinion B is chosen with probability (1 − k). The value of k satisfies 0 ≤ k ≤ 1 and is a function of the distribution of prejudices within the social group. • The inflexibles also vote to determine the local majority, but contrary to the floaters, in case they hold the minority choice, they stick to it. They are stubborn and keep on with their own pre-decided choice whatever the local majority is. Accordingly, an A-inflexible stays in state 1 and a B-inflexible stays in 0. The same holds true at a tie. Their respective proportions denoted as a and b are external fixed parameters with the constraint 0 ≤ a + b ≤ 1. At time t, once a scheme is completed with p t → p t+1 , another one is performed to obtain p +1 → p t+2 and so forth till the debate ends with an eventual vote at a given time, which determines the total number of updates to be implemented. The frequency of updates is a function of the intensity of the ongoing debate. For any real situation, the debate initial proportion p 0 is evaluated using polls.
Let us now evaluate the function P (r) a,b,c,k yielding p t+1 from p t , given the values, as follows: However, since the contrarian phenomenon is mathematically identical to a random flipping of floaters with probability c among reshuffled agents, we can decouple the c effect from the local update writing as which simplifies as To evaluate P (r) a,b,k , we note that in a given configuration of a group of size r with (r − μ) agents holding opinion A and μ agents holding opinion B, the contributions to P (r) a,b,k result from two different families. One family includes contributions with a majority of A and equality of A and B (for even size at a tie with probability k), while the other family corresponds to contributions with a minority of A and equality of A and B (for even size at a tie with probability (1 − k)). These families are denoted, respectively, as P (r,μ) a,b,c and Q (r,μ) a,b,c under the constraint μ ≤ [r/2], where [x] is the integer part of x. Eq. 1 can be rewritten as which allows factorization of the k dependence. The quantity P (r,μ) a,b (p), which accounts for the contribution to A after one update from configurations with (r − μ) agents with opinion A and μ agents with opinion B, can be decomposed as the sum of contributions with α A-inflexibles and β B-inflexibles, where integer α runs from 0 to (r − μ) and β runs from 0 to μ giving (see Figure 1 left) Since μ ≤ [r/2] (A majority or tie), contributions to p t+1 from Eq. 6 come from all agents except B-inflexibles minus contrarians after the update, yielding Similarly, the quantity Q (r,μ) a,b (p), which accounts for the contribution to A from configurations with μ agents with opinion A and (r − μ) agents with opinion B, can be decomposed as the sum of contributions with α 0, . . . , μ A-inflexibles and β 0, . . . , (r − μ) B-inflexibles giving (see Figure 1 right) Since μ ≤ [r/2] (A minority or tie), contributions to p t+1 from Eq. 8 come only from A-inflexibles after the update, yielding With the use of the formulas (x + y) n n j 0 n j x n−j y j and ny(x + y) n− 1 n j 0 n j jx n−j y j , the summation over α and β leads us to and Frontiers in Physics | www.frontiersin.org November 2020 | Volume 8 | Article 566580 With the use of identities and we arrive at the compact expression of the evolution function P (r) a,b,k for general group size r in the form where Note that the relation Π (r,μ) 2 (p, k) Π (r,μ) 1 (1 − p, 1 − k). Also, note that the relation This guarantees the covariance of P (r) a,b,k (p) with respect to the renaming of opinions A and B as follows: At this stage, to obtain the complete update equation, we use Eq. 3 as which allows calculation of the opinion dynamics for any set of parameters (a, b, c, k) given any group size r for any initial support p 0 for opinion A. We thus have calculated a universal formula to predict opinion dynamics in a parameter space of five dimensions. We now go one step further to make our equation further realistic by considering a distribution of size with r 1, 2, . . . , L, where L is the largest update size. Usually, in most social situations, L is around 4, 5, or 6. The size weight w r of groups of size r has to be evaluated from observation under the constraint r L r 1 w r 1. Including the size r 1 allows consideration of agents who do not take part in local discussion during each update. Then, using Eq. 2, the associated global proportion of A supporters becomes In principle, Eq. 21 allows one to contribute to the issue of connecting the topology of a given network and the dynamics occurring through the network [45]. Indeed, the set of values of weights w r and L could then be extracted from the network.

A FEW ILLUSTRATIONS OF SUDDEN AND UNEXPECTED MINORITY OUTBREAKS
To make our universal update equation more concrete, we list explicit expressions for the series of values r 3, 4, 5, 6, 7, 8, 9 in Appendix A. In addition, to distinguish the dynamical effects that come from the current update equation from the ones already present in the former model, we recall that the impact of Frontiers in Physics | www.frontiersin.org November 2020 | Volume 8 | Article 566580 unconscious prejudices has been studied for group size r 4 and the effect of having inflexible or stubborn agents has been studied for groups of size 3. Each yields separately the phenomenon of minority spreading as exhibited for instance with k 1 and a 0.20 and b 0 in Figure 2. The corresponding update formulas are recovered from Eq. 2 with P (4) 0,0,0,1 (p) Π (4) 0 (p, k) p 2 (3p 2 − 8p + 6) and P (3) 0.20,0,0,k (p) Π (3) 0 (p, k)+ 0.20Π (3) 1 (p, k) −2p 3 + 3.20p 2 + 0.20(1 − 2p). Note that P (3) 0.20,0,0,k (p) is independent of k as expected for an odd-size group. Minority spreading occurs in both cases, but rather slowly for the second one.
While each effect was accounting for, alone, now the universal formula allows us to investigate the combination of both effects, either going along the same support for A (P (4) 0.20,0,0,1 (p)) or competing for and against A (P (4) 0,0.20,0,1 (p)) as shown in Figure 3 for the case r 4. Combination enhances drastically the minority spreading, but competition shows that 20% of B-inflexibles do overcome the full benefit of the prejudice effect.
We proceed to illustrating the capacity of the current update equation to yield sudden and unexpected minority outbreaks exhibiting a couple of striking cases with groups of sizes r 3 and r 4.
In Figure 4, each graph shows two curves for the evolution of

FIXED POINTS OF THE DYNAMICS
The dynamics implemented by repeated applications of Eq. 2 exhibits a rather large spectrum of different scenarios within the The phase diagram landscape is shaped by the various attractors and tipping surfaces, which are the solutions of the fixed-point equation It is of interest to mention that Eq. 22 is a polynomial of degree r in p and thus exhibits r solutions of which no more than three are real and contained within the 0 − 1 range. This assessment results from playing with the equation and hand-waving arguments but a mathematical proof is still on hold.
In case of three fixed points p + 0 , p + s , and p + 1 in ascending order, the smallest p + 0 ≤ 1/2 is stable and represents B-majoritarian final state, while the largest p + 1 ≥ 1/2 is also stable, representing Amajoritarian final state. The medium-valued p + s is unstable, acts as a separator for the basins of attraction to p + 0 and p + 1 , and is a tipping point of the dynamics.
Since making a visual representation is impossible in five dimensions, being interested in the evolution of an initial value p 0 given fixed values of (a, b, c, k, r), the operative use of the phase diagram is to select two-dimensional slices showing the evolution of p 0 as a function of repeated updates with p 0 → p 1 → . . . → p n , where n is the number of iterations. With respect to prediction about a real event, what matters is to determine if p n > 1/2 (opinion A victory), p n < 1/2 (opinion A failure), or p n ≈ 1/2 (hung outcome).
An alternative practical use of the phase diagram is to extract the two-dimensional slices, which shows the function p t+1 P (r) a,b,c,k (p t ) for a fixed set of values (a, b, c, k, r). These curves display the eventual attractors and tipping points underlying the dynamics from which predictions can be made. These points are located at the crossing of p t+1 P (r) a,b,c,k (p t ) and the diagonal p t+1 p t . Indeed, all "slices" share the common property of having at least one single attractor for the dynamics. In addition, a series of slices exhibit one additional attractor and a tipping point located between the two attractors. For those cases, varying some of the parameters (a, b, c, k) may lead either to have one attractor and the tipping point to coalesce at critical values, yielding then a single-attractor dynamics. The other scheme is having the two attractors to merge at the tipping point to produce another singleattractor dynamics. To have a single-attractor dynamics implies one identified opinion is certain to win whatever its initial  support is. This means that the debate or the campaign duration lasts for enough time to cross 1/2, i.e., 50%, of the ballots for an election. Figure 5 and Figure 6 show a series of cases illustrating the above two scenarios.

EXPLORING THE PHASE DIAGRAM
From Eq. 22, when b c 0, increasing the parameter a makes p + 0 and p + s merge into a single value at a a c and then disappear to make p + 1 the sole final state of the system (see Figure 7). The critical value a for b 0, which we call a c (c), is obtained from 1 − z p P (r) ac(c),0,c,k p + 0.
In particular, for c 0, the critical value a c (0), which we simply call a c , and its associated p + c are obtained from With small but non-zero b, the system goes through transition between two stable fixed-point phase and single fixed-point phase, when a is varied, at a critical value higher than a c . Above a certain value of b, the system goes from B-majoritarian single fixed-point phase to A-majoritarian single fixed-point phase without passing through three fixedpoint phase (see Figure 7). The transition is characterized by triple critical point a b a t (c): Limiting ourselves to c 0 for now, the triple point a t a t (0) and its associated p + t are obtained as p + t 1/2 and It is instructive to draw the phase diagram on an {a, b} plane.
There is a region of small values of a and b in which final majority can go either way depending on its initial support. For large values of a and/or b, final majority is predetermined due to the strong influence of inflexibles. When a or b exceeds a t , two inflexible-dominated regions are placed next to each other   Figure 7.
The r-dependence of a c and a t can be seen in Figure 8. We list just some of them as follows: For r 3, we have a c 0.1714 and a t 0.25, and for r 5, a c 0.2104 and a t 0.2917. For r 7, we have a c 0.2358 and a t 0.3167, and for r 9, a c 0.2452 and a t 0.3339.
Overall, approaching r ∞limit, a r a t 0.5 is very slow, and for reasonably small group size r ≈ 10, a c ≈ 1/4 and a t ≈ 1/3 hold, which are closer to the case r 3 than r ∞. Even at r ≈ 50, we have surprisingly small a c ≈ 1/3 and a t ≈ 2/5.
It is again instructive to look at the phase diagram on the {a, b} plane with different values of c (Figure 9). It should be very clear now that for all groups of size r, the effect of contrarians on the final majority formation is to decrease the role of floaters and increase the power of inflexibles. This fact, which has originally been found in r 3, for example, turns out to be a generic feature of the Galam model.

SUMMARY
In this study, we have obtained a universal formula for the temporal evolution of agents following the Galam opinion dynamics in a parameter space of five dimensions, which are the respective proportions of inflexibles of each side (stubbornness), the proportion of contrarians, the mean value of shared prejudices, and the update group size.
The associated opinion landscape is found to be shaped by several attractors and tipping points, which yield a rich variety of non linearities and singularities in the opinion flows. Sudden upheavals such as minority spreading and majority collapse are thus given a rationale unveiling the hidden mechanisms behind the occurrence of unexpected and sudden shifts in the distribution of opinions such as with the Brexit victory and Trump election. The time dependence of the corresponding phenomena is also exhibited.
For large group sizes, although the effects of inflexible agents waved out with simple majority rule holding, the results vary very slowly, showing that earlier insights obtained from group sizes three and four remain intact. In contrast, for even sizes, although the prejudice effect weakens with increasing size, it stays effective. Moreover, having the update equation for any group size r makes it possible to consider combinations of group sizes, which in turn opens the path to account for underlying networks.
The study of one specific case has showed the existence of critical points a c and a t , which corner and branch out the lines separating the inflexibles-dominant and floaters-determinable phases. The admixture and increase of contrarians effectively assist the dominance of inflexibles and reduce the parameter region in which initial composition of floaters can determine the outcome of majority opinion formation. The increase in group size r induces modest but clear increase in both a c and a t . Accordingly, when the local discussion involves more agents, a larger committed minority is necessary to impose its will on the majority, or, identically, a larger enlightened minority is necessary for its persuasion of the majority.
Obtaining the complete phase diagram of the dynamics of opinions yields a robust forecasting frame for which predictions become more reliable since what matters is the identification of the basin of attraction in which the dynamics is taking place, thus providing some flexibility in the accuracy of parameter evaluation. However, along the basin boundaries, higher precision is required for estimation of the value of the FIGURE 7 | An example of the phase diagram of the parameter space {a, b}. The group size here is chosen to be r 9. The regions marked as A, B, and A/B represent parameter values with which the system converges unconditionally to A majority, unconditionally to B majority, and to either A or B majority depending on the initial configuration, respectively.