The Complex Science of Cyberdefense: Computer Immunology

Threats are ubiquitous in complex systems: biology is rife with viruses, parasites, and bacteria; social networks abound with bullies; and international relations are stymied by rogue nations. In the second of three lectures, Stephanie Forrest proposes that understanding how complex systems generally...

Software Engineering: Evolving Computer Programs

Software -- used today for everything from shopping and banking to streaming movies -- shapes our daily experience. The software industry contributes billions of dollars annually to the U.S. economy and employs millions of Americans. Programmers like to think of software as the carefully crafted product...

An Exactly Solvable Model of Racial Segregation

In the 1960s and 70s Thomas C. Schelling, an economist then at Harvard, developed a simple agent-based simulation in which a mixed population of two races spontaneously breaks down into segregated enclaves, even though no member of the population seeks that outcome. Many variations of Schelling's model...

Cancer Evolution and Prevention

Since the mid 1970s, cancer has been described as a process of Darwinian evolution, with somatic cellular selection and evolution being the fundamental processes leading to malignancy and its many manifestations (neoangiogenesis, evasion of the immune system, metastasis, and resistance to therapies)....

On Moral Progress: Is the Human Conscience Led by the Head or the Heart?

Is the human conscience led by the head or the heart? Is the moral progress we have enjoyed – religious freedom, the abolition of slavery, anti-war movements, civil, women’s, and gay rights – a gift of empathy and emotion, or of reason and logic? Psychologist and author Steven Pinker and philosopher...

Criticality in the Plasma Membrane of Living Cells

The plasma membrane is a two dimensional liquid composed of a diverse soup of lipids and embedded proteins that surrounds all living cells. In addition to separating inside from outside, the plasma membrane contains much of the cell’s machinery for receiving and processing information. Recent experiments...

A Variational Bayes Approach to Robust Principal Component Analysis

We solve the Robust Principal Component Analysis problem: decomposing an observed matrix into a low-rank matrix plus a sparse matrix. Unlike alternative methods that approximate this L0 objective with an L1 objective and solve a convex optimization problem, we develop a corresponding generative model...

Evolvability and the Tradeoff between Specificity and Efficiency in Biology

The questions of “How and Why” have underlain biological investigation since the Greeks. Darwin’s answer, largely on the anatomical, physiological and behavioral level, was his theory of evolution by natural selection. Yet for natural selection to be completely satisfactory, we needed to understand...

Looking at Legal Structures through Historical Data

Of human institutions, legal systems are some of the most in influential and quite often, the least well understood. In addition to economic and cultural motivations, legal systems, particularly formalized and precedent based ones, tend to generate endogenous motivations. That is, motivations that arise...

Avoiding Collapse: Detecting Signals for Critical Transitions in Agent-Based Ecological Models

A variety of complex systems have critical thresholds that, once crossed, find these systems shifting abruptly from one state to another. There has been a great deal of theoretical work utilizing statistical and spatially analytic methods for detecting early warnings of such critical transitions across...

Cancer as a Failure of Multicellularity: The Role of Cellular Evolution

Cancer results from a process of cellular evolution. Key cancer vulnerabilities and defenses arose from the ancient evolutionary transition from single-celled to multicellular organisms. Because cellular evolution leads inexorably to cancer, organismal evolution has organized cell reproduction into patterns...

Bubbles and Crashes in a Heterogeneous-Agent

We construct a heterogeneous-agent model of a single-asset financial market in which agents form demand for the asset based on price forecasts. Agents can change their forecasts over time in response to market conditions (in particular, price volatility and previous prices). We simulate this model and...

Linking Pattern and Process in Cultural Evolution

This work aims to lay the theoretical and methodological foundations for investigating how individual level interactions aggregate to produce population level patterns of cultural diversity. Cultural traits can be transmitted between individuals in different ways. Here we investigate the dynamics produced...

How the Biological Sciences Misquantify Diversity, and Why It Matters

Diversity plays a central role in ecology, conservation biology, genetics, and other fields. Yet most of the classical measures of compositional complexity, generalized entropy, and diversity, and the measures of compositional differentiation and similarity that biologists derived from them, do not...

New problems, New Partnerships: What Tomorrow's University Must Be

In a relatively brief 150 years, human demands on natural systems have, perhaps irrevocably, brought us to an inflection point – the implications of which we do not yet fully understand. Meeting these new and increasingly complex challenges will require massive, coordinated efforts linking academia,...

Cities through the Ages: One Thing or Many?

I address the question of whether the urban scaling laws identified for modern cities by Bettencourt, West, and others should apply to premodern cities. I propose a dichotomy between economic cities (mostly contemporary cities, whose growth is generated by agglomeration effects and commercial expansion)...

Epidemics on Networks with Applications to Network Robustness against Malware Spread and to Information Dissemination in Social Networks

We concentrate on the simple SIS epidemics on any network. First, general (exact) properties are derived, followed by a mean-field approximation that culminates in the N-intertwined approximation (NIMFA). Several extensions and attractive features of NIFMA are presented. Since there does not exist an...

A Theory of Collective Reputations with Endogenous Identity

We explore a formal economic model of "collective reputations" — i.e., of the rational formation by external observers of beliefs about the unobserved traits of varied population aggregates. This phenomenon (sometimes referred to as 'stereotyping') has long been of interest to economists, sociologists,...

Understanding the Impact of Human Behavior and Heterogeneous Mixing Patterns on Social Networks and Epidemics

Social and mass media have recently played a crucial role in informing and influencing people’s perceptions about the spread of infectious diseases. Community perception can influence human behavior, which can in turn impact the spread of an epidemic by changing the social contact network within the...

Why is Time a One-Way Street?

Anyone can see that the past is different from the future. Anyone, that is, but theoretical physicists, whose equations do not seem to distinguish the past from the future. How, then, do physicists understand the "arrow of time" — the fact that the past and future are so different? Leonard Susskind...