Physical mechanism underlying opinion spreading
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Physical Mechanism Underlying Opinion Spreading. Jia Shao Advisor: H. Eugene Stanley. J. Shao, S. Havlin, and H. E. Stanley, Phys. Rev. Lett. 103 , 018701 (2009). Questions. How do different opinions influence each other in human society? Why minority opinion can persistently exist?.

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Physical Mechanism Underlying Opinion Spreading

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Physical mechanism underlying opinion spreading

Physical Mechanism Underlying Opinion Spreading

Jia Shao

Advisor: H. Eugene Stanley

J. Shao, S. Havlin, and H. E. Stanley, Phys. Rev. Lett. 103, 018701 (2009).


Questions

Questions

  • How do different opinions influence each other in human society?

  • Why minority opinion can persistently exist?


Motivation

Motivation

US presidential elections

  • Public opinion is important.

  • Simulation of opinion formation is a challenging task, requiring reliable information on human interaction networks.

  • There is a gap between existing models and empirical findings on opinion formation.

Instead of using individual level

network, we propose a community

level network to study opinion

dynamics.


Outline

Outline

  • Part I: Empirical findings from presidential election

  • Part II: Invasion Percolation

  • Part III: We propose a dynamic opinion model which can explain the empirical findings


2008 presidential election

Part I

2008 Presidential Election

We study counties with f>fT

fDem

fT=0.8

fT=0.5

fT=0.3

http://www-personal.umich.edu/~mejn/election/2008/


Counties in southern new england

Part I

Counties in southern New England


Counties in southern new england1

Part I

Counties in southern New England


Counties in southern new england2

Part I

Counties in southern New England

Vote for Obama

Barnstable f=55%

Polymouth f=54%

Norfolk f=54%

Worcester f=57%

Fairfield f=52%

Litchfield f=47%

Windham f=53%

Kent f=56%


Counties in southern new england3

Part I

Counties in southern New England

County network of f>fT=0.6

Number of counties:17

Size of largest cluster: 10


County network of obama

Part I

County Network of Obama

Counties of fObama>fT

50% decrease


County network of mccain

Part I

County Network of McCain

Counties of fMcCain>fT

30% decrease


Clusters formed by counties when f t f c

Part I

Clusters formed by counties when fT=fc

Cluster Size

County network

Diameter

Fractal dimension: dl=1.56

=1.86

The phase transition in county network is

different from randomized county network.


Physical mechanism underlying opinion spreading

  • The real life county election network demonstrates a percolation-like phase transition at fT=fc.

  • This phase transition is different from random percolation.

What class of percolation does this phase transition

belong to?


Invasion percolation

Part II

Invasion Percolation

Example: Inject water into earth layer containing oil

  • Invasion percolation describes the evolution of the front between two immiscible liquids in a random medium when one liquid is displaced by injection of the other.

  • Trapped region will

    not be invaded.

A: Injection Point

P. G. de Gennes and E. Guyon, J.Mech. 17, 403(1978).

D. Wilkinson and J. F. Willemsen, J. Phys. A 16, 3365 (1983).


Invasion percolation1

Part II

Invasion Percolation

Trapped Region of size s

P(s) ~ s-1.89

S

Fractal dimension: 1.51

s ~l1.51

S. Schwarzer et al., Phys. Rev. E. 59, 3262 (1999).


Physical mechanism underlying opinion spreading

  • The phase transition of the county election network belongs to the same universality of invasion percolation.

  • Why invasion percolation?

  • How can we simulate the dynamic process of opinion formation?


Evolution of mutually exclusive opinions

Evolution of mutually exclusive opinions

: =2:3

Time 0

: =3:4

Time 1

stable state

(no one in local

minority opinion)

Time 2


A opinion spread for initially

A. Opinion spread for initially

: =2:3

stable state : =1:4


B opinion spread for initially

B. Opinion spread for initially

: =1:1

stable state : =1:1


Phase transition on square lattice

“Phase Transition” on square lattice

Phase 1

Phase 2

B

largest

size of the second

largest cluster

×100

A

critical initial fraction fc=0.5


2 classes of network differ in degree k distribution

Edges connect randomly

Preferential Attachment

2 classes of network: differ in degree k distribution

Poisson distribution: Power-law distribution:

(i) Erdős-Rényi

(ii)scale-free

µ

µ

Log P(k)

µ

Log k


Phase transition for both classes of network

“Phase Transition” for both classes of network

fc≈0.46

fc≈0.30

(b) scale-free

(a) Erdős-Rényi

µ

Q1: At fc , what is the distribution of cluster size“s”?

Q2: What is the average distance“r” between nodes belonging to the same cluster?


Clusters formed by minority opinion at f c

Clusters formed by minority opinion at fc

r

Cumulative distribution function

P(s’>s) ~ s-0.89

r/s(1/1.84)

Const.

s ~ r1.84

PDF P(s) ~ s-1.89

Conclusion: “Phase transition” of opinion model belongs to the

same universality class of invasion percolation.


Summary

Summary

  • There exists a phase transition in the county election network when changing fT.

  • The phase transition of county network can be mapped to oil-field-inspired physics problem, “invasion percolation”.

  • We propose a network model which can explain the empirical findings.


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