Finding simplicity in complex systems Luís M. A. Bettencourt
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Finding simplicity in complex systems
Luís M. A. BettencourtTheoretical Division, Los Alamos National LaboratorySanta Fe institute
Each piece, or part, of the whole nature is always an approximation to the complete truth, or the complete truth so far as we know it. In fact, everything we know is only some kind of approximation.
The Feynman Lectures on Physics (1964)
Taming Complex Systems
Measuring new and better thingsgenome, pathogens, medicine, ecosystems, science & technology, computer networks,nations, cities, organizations, individuals.
Big Data data are enormous, varied, growing exponentially
So what? do we have better public health?
policy? science and technology? more efficient markets?
Why (not)?
The problem:familiarity, observation vs. experiments, drowning in data, entanglement, speed, scope The answer [this talk]:
most things don’t matter!
but some things matter a lot: know what’s important!
measureinfer mechanism act fast act systematicallyiterate
approximately!
newsamanda knox
contagion processesthe early history
source: wikipediaHand bill from the New York City Board of Health, 1832
Life photo archive /Google Images.
These miserable outcasts called that "fumigating" us, and the term was a tame one indeed. They fumigated us to guard themselves against the cholera, though we hailed from no infected port. We had left the cholera far behind us all the time. However, they must keep epidemics away somehow or other, and fumigation is cheaper than soap.
RANT, RANT, RANT
Mark Twain 1867
The datasoho london
(1854)
Prockter, A. photo image, Feb. 23, 2006.
7th September, 1855
Cady Staley and Geo. S. Pierson, The Separate System of Sewerage, Its Theory and Construction
(New York: D. Van Nostrand, Co., 1899), p. 33.
“Whenever you can, count.”
Francis Galton
the nature of branching processes
Most complex systems operate fast and extensively
by triggering and regulating cascades
Nk= bk Nk-1 k ~ time, space,...
b>1 supercritical blows up b=1 critical = thresholdb<1 subcritical fizzles out
b is some
complicated
function
b=2
in epidemics b = contact rate x infectious time
Motor Control
Generalized 3 Hz spike and wave discharges in a child with childhood absence epilepsysource: wikipedia
Epileptic Seizure
HIV vs the human immune systeminformation arms races
Highly Active Antiretroviral Therapy (HAAT) or “drug cocktail”
give the immune system a hand by
reducing b for the virus
anti-retroviral drugs
Proof: no a priori predictability of new trends is possible [early predictability very unreliable]
network visibility (number of incoming-links) leads to the emergence and reinforcement of
(just as dumb) market makers
information cascadesheuristics of decision making under uncertainty
when in doubt imitate
Bikhchandani, S., Hirshleifer, D., and Welch, I. (1992)
Bettencourt (2002-3) arXiv:cond-mat/0212267arXiv:cond-mat/0304321
The spread of scientific ideasUSA, Japan, USSR
The power of a good ideaQuantitative modeling of the spread of ideas from epidemiological modelsBettencourt et al Physica A (2006), Scientometrics (2008), PNAS (2011)
much of what we do in society makes sense in light of information transmission
increase contact rate &
citiesmeetings
phd programspostdocs
search engines
increase lifetime of information
data storagewritten documentslibraries & archives
databases
b = contact rate x lifetime of information
It’s all about b [networks]
don’t need to know it measure it!
but what about uncertainty? predict and measure it!
what about understanding, control? act, predict and measure it!
Marburg Hemorrhagic FeverUige, Angola 2005
89% death rate
observation model prediction inferred mechanism
Bettencourt (2006) in Mathematical and Statistical Estimation Approaches in EpidemiologySpringer
good idea!
measurepredictmeasureanomaly?iterate
swine flu pandemicMexico 2009
shut down Mexico City20 million people
but with mixed resultsworld pandemic
Neo dodging bulletsThe matrix
b=1.3 for influenza (b<3)
infectious period ~ days
information technology ~ fraction of second
Faster than the speed of life
Computers are now being used to generate news stories about company earnings results or economic statistics as they are released. This almost instantaneous information is fed directly into other computers, which trade on the news.
City trusts computers to keep up with the news
Aline van Duyn, Financial Times, April 16 2007 03:00
Taming complexity is a wicked problem
but often it is enough to know what is critical
[failure modes, instabilities, cascades]
it is easier to be simple-minded but fast* than slow and complex
* but you’ve got to learn
action mechanisms need to be further developed