(Digital) networks and the science of complex systems

1. (Digital) networks and the science of complex systems Kaj Kolja Kleineberg | [email protected] @KoljaKleineberg | koljakleineberg.wordpress.com

2. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Agenda: From complex systems to digital networks 1. Networks and complex systems 2. The power of digital networks 3. Sustaining digital diversity 4. Summary 2

3. NETWORKS AND COMPLEX SYSTEMS

4. Networks and complex systems The power of digital networks Sustaining digital diversity Summary A chess riddle: Swap the positions of the black and white knights 4Credits: Marian Boguna

5. Networks and complex systems The power of digital networks Sustaining digital diversity Summary A chess riddle: Network approach makes the problem really easy 5Credits: Marian Boguna

10. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Seven bridges of Knigsberg: crossing each bridge only once The city of Knigsberg was set on both sides of the Pregel River, and included two large islands which were connected to each other, or to the two mainland portions of the city, by seven bridges. The problem was to devise a walk through the city that would cross each of those bridges once and only once. 6

11. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Seven bridges of Knigsberg: the foundation of graph theory https://en.wikipedia.org/wiki/Seven_Bridges_of_Knigsberg Is it possible to cross all bridges only once? 7

12. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Seven bridges of Knigsberg: the foundation of graph theory https://en.wikipedia.org/wiki/Seven_Bridges_of_Knigsberg Is it possible to cross all bridges only once?Whenever one enters a node by a bridge, one leaves the node by a bridgeThe number of times one enters a non-terminal node equals the number of times one leaves it even number except for startendpointHowever, all nodes have uneven number of bridges attached Contradiction 7

13. Networks and complex systems The power of digital networks Sustaining digital diversity Summary complex networks 8

14. Networks and complex systems The power of digital networks Sustaining digital diversity Summary complex networks Complex networks are maps of complex systems. 8

15. Networks and complex systems The power of digital networks Sustaining digital diversity Summary What is a complex system? 9

16. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Definition: What is a complex system? ...the whole is more than the sum of the parts, [...] in the sense that, given the properties of the parts and the laws of their interaction, it is not a trivial matter to infer the properties of the whole. Herbert A. Simon 10

17. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Definition: What is a complex system? ...the whole is more than the sum of the parts, [...] in the sense that, given the properties of the parts and the laws of their interaction, it is not a trivial matter to infer the properties of the whole. Herbert A. Simon Large number of components 10

18. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Definition: What is a complex system? ...the whole is more than the sum of the parts, [...] in the sense that, given the properties of the parts and the laws of their interaction, it is not a trivial matter to infer the properties of the whole. Herbert A. Simon Large number of components Nonlinear interactions 10

19. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Definition: What is a complex system? ...the whole is more than the sum of the parts, [...] in the sense that, given the properties of the parts and the laws of their interaction, it is not a trivial matter to infer the properties of the whole. Herbert A. Simon Large number of components Nonlinear interactions Emergent behavior 10

20. Networks and complex systems The power of digital networks Sustaining digital diversity Summary A car is not a complex system (we call it a difficult system) 11

21. Networks and complex systems The power of digital networks Sustaining digital diversity Summary The Internet is a complex system (without a central masterplan) 12

22. Networks and complex systems The power of digital networks Sustaining digital diversity Summary The Internet is a complex system: lack of scale 13Nature, 401:130-131 (1999)

23. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Scale-free property common to many real complex networks induces a vanishing epidemic threshold 14

24. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Networks allow us to map interactions and study system-level implications 15Nature Physics 10, 762-767 (2014); Phys. Rev. Lett. 109, 064101 (2013)

25. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Financial networks and systemic risk (debt rank) 16

26. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Similar procedure allows Google to rank websites (page rank) 17

27. THE POWER OF DIGITAL NETWORKS

28. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Facebook likes predict your personality better than your spouse 19

29. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Social messages can influence real world voting behavior 20

30. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Search algorithms can also change real world voting behavior 21

31. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Algorithms can change how you feel by changing your Facebook timeline 22

32. Networks and complex systems The power of digital networks Sustaining digital diversity Summary What if all this power is in one hand? 23

33. SUSTAINING DIGITAL DIVERSITY

34. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Model contains spreading dynamics and the influence of mass media Online social network layer Traditional contact network layer Active Onlineoffline Passive Onlineoffline Susceptible Only offline 25

35. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Model contains spreading dynamics and the influence of mass media Online social network layer Traditional contact network layer Active Onlineoffline Passive Onlineoffline Susceptible Only offline Mass media activation Viral activation Deactivation Viral reactivation 25

36. Networks and complex systems The power of digital networks Sustaining digital diversity Summary The evolution of isolated online social networks: insights from a system-level description Underlying social structure determines topological evolution PRX 4, 031046, 2014 27

37. Networks and complex systems The power of digital networks Sustaining digital diversity Summary The evolution of isolated online social networks: insights from a system-level description Underlying social structure determines topological evolution Balance of viral and mass media influence PRX 4, 031046, 2014 27

38. Networks and complex systems The power of digital networks Sustaining digital diversity Summary The evolution of isolated online social networks: insights from a system-level description Underlying social structure determines topological evolution Balance of viral and mass media influence Survival and death of networks PRX 4, 031046, 2014 27

39. Networks and complex systems The power of digital networks Sustaining digital diversity Summary The evolution of isolated online social networks: insights from a system-level description Underlying social structure determines topological evolution Balance of viral and mass media influence Survival and death of networks Weak ties have higher transmissibility PRX 4, 031046, 2014 27

40. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Digital ecosystem is formed by multiple networks competing for the attention of individuals OSN 2 OSN 1 Underl. network Active Passive Susceptible Partial states} Virality share distribution between OSNs i = i(a) Rich-get-richer more active networks obtain higher share Here: i = [a i ]/ j[a j] : activity affinity 28Sci. Rep. 5, 10268 (2015)

41. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Coexistence (diversity) is possible but fragile: once lost, it cannot be recovered Stable Unstable 0.50 0.75 1.00 1.25 1.50 0.00 0.25 0.50 0.75 0.00 0.25 0.50 0.75 Bifurcation diagram 1,2 a 29Sci. Rep. 5, 10268 (2015)

42. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Coexistence (diversity) is possible but fragile: once lost, it cannot be recovered Stable Unstable 0.50 0.75 1.00 1.25 1.50 0.00 0.25 0.50 0.75 0.00 0.25 0.50 0.75 Bifurcation diagram 1,2 a Coexistence despite rich-get-richer 29Sci. Rep. 5, 10268 (2015)

43. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Coexistence (diversity) is possible but fragile: once lost, it cannot be recovered Stable Unstable 0.50 0.75 1.00 1.25 1.50 0.00 0.25 0.50 0.75 0.00 0.25 0.50 0.75 Bifurcation diagram 1,2 a Coexistence despite rich-get-richer Digital diversity is irreversible 29Sci. Rep. 5, 10268 (2015)

44. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Network of multi-layer networks represents global digital ecology Active Passive Susceptible Partial states} Local network Global network Effective activity 30

45. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Digital networks can coexist but coexistence is fragile Coexistence despite rich-get-richer Sci. Rep. 5, 10268 (2015) Sci. Rep. 6, 25116 (2016) 32

46. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Digital networks can coexist but coexistence is fragile Coexistence despite rich-get-richer Diversity is fragile Sci. Rep. 5, 10268 (2015) Sci. Rep. 6, 25116 (2016) 32

47. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Digital networks can coexist but coexistence is fragile Coexistence despite rich-get-richer Diversity is fragile Moderate digital diversity observed Sci. Rep. 5, 10268 (2015) Sci. Rep. 6, 25116 (2016) 32

48. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Digital networks can coexist but coexistence is fragile Coexistence despite rich-get-richer Diversity is fragile Moderate digital diversity observed Facebook takes over local networks Sci. Rep. 5, 10268 (2015) Sci. Rep. 6, 25116 (2016) 32

49. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Utility of networks: bottom-up search and navigation with incentives based on sharing generated value Navigation is common function networks perform 33Nature Communications 1, 62 (2010) Scientific Reports 7, 2897 (2017)

50. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Utility of networks: bottom-up search and navigation with incentives based on sharing generated value Navigation is common function networks perform Individuals perform routing instead of service providers 33Nature Communications 1, 62 (2010) Scientific Reports 7, 2897 (2017)

51. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Utility of networks: bottom-up search and navigation with incentives based on sharing generated value Navigation is common function networks perform Individuals perform routing instead of service providers Payoff for successful deliveries 33Nature Communications 1, 62 (2010) Scientific Reports 7, 2897 (2017)

52. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Navigation works better with more active networks 35Nature Physics 12, 10761081 (2016)

53. Networks and complex systems The power of digital networks Sustaining digital diversity Summary Appropriate incentives could create a feedback loop building on self-organization of complex systems Qualied Money t o route activein m any networks Optim izes strategy: Inc entive Sustains digital dive rsity Increasesro uting perform a nce Exchangeable Social Bitcoin +Reputation Feedback loop can overcome fragility Digital diversity can become robustsustainable 36Eur. Phys. J. Spec. Top. 225: 3231 (2016)

54. SUMMARY

55. Networks and complex systems The power of digital networks Sustaining digital diversity Summary (Digital) networks and the science of complex systems Complex systems: emergent behavior, no central control 38

56. Networks and complex systems The power of digital networks Sustaining digital diversity Summary (Digital) networks and the science of complex systems Complex systems: emergent behavior, no central control Networks are system level maps of interactions 38

57. Networks and complex systems The power of digital networks Sustaining digital diversity Summary (Digital) networks and the science of complex systems Complex systems: emergent behavior, no central control Networks are system level maps of interactions Digital networks are extremely powerful 38

58. Networks and complex systems The power of digital networks Sustaining digital diversity Summary (Digital) networks and the science of complex systems Complex systems: emergent behavior, no central control Networks are system level maps of interactions Digital networks are extremely powerful Digital diversity could be sustained with incentives 38

59. Kaj Kolja Kleineberg: [email protected] @KoljaKleineberg koljakleineberg.wordpress.com ETH Zurich: Computational Social Science Group http://www.coss.ethz.ch

60. Kaj Kolja Kleineberg: [email protected] @KoljaKleineberg Slidesupdates koljakleineberg.wordpress.com ETH Zurich: Computational Social Science Group http://www.coss.ethz.ch

61. Kaj Kolja Kleineberg: [email protected] @KoljaKleineberg Slidesupdates koljakleineberg.wordpress.com References ETH Zurich: Computational Social Science Group http://www.coss.ethz.ch