Taxi shareability

If people shared taxis with strangers, how much money could be saved? And how much could pollution and traffic be reduced? A dataset of 150 million taxi trips and a new type of mathematical analysis enabled the untapped potential of New York City’s fleet of more than 13,000 taxis to be quantified.



Dynamics of social balance

“The enemy of my enemy is my friend” – what are the mathematical consequences of playing out this logic in large social or political networks? Tools from statistical physics, graph theory, and random matrix theory bring out the surprising implications of this ancient approach to friendship and rivalry.



Dynamics of political moderation

In a simple model of a society polarized by ideological conflict, how can moderation be encouraged? Under what conditions will a committed minority of true believers eventually win everyone over to their point of view?

Chimera states for coupled oscillators

Systems of identical oscillators with symmetrical coupling can sometimes split into two domains, one synchronized, the other desynchronized. The properties of such a “chimera state” have been elucidated by exactly solvable models.

Crowd synchronization on the Millennium Bridge

What caused London’s Millennium Bridge to wobble on its opening day? And why did the pedestrians on it inadvertently fall into step with its sideways vibrations? A model based on ideas from mathematical biology explains both effects as two sides of the same coin.

Dynamics of language death

The world’s languages are vanishing at an alarming rate. Modeling the competition between languages with the tools of population dynamics led to the first quantitative model of language decline.



Percolation on random graphs

Mathematical studies of the Internet, social networks, and the power grid have addressed the resilience of these networks to either random or targeted deletion of network nodes. Percolation models on random graphs with arbitrary degree distributions can be solved exactly to illuminate this issue of network resilience.

Small-world networks

How can all seven billion of us be just six handshakes apart? “Small-world networks,” introduced by Strogatz and his former graduate student Duncan Watts, give one possible explanation. The same math also gives insight into how epidemics spread, how brains are wired, and how blackouts propagate through the power grid.



Dynamics of Josephson junction arrays

Josephson junctions are superconducting electronic devices that obey the same governing equations as pendulums – but they swing a hundred billion times faster. When thousands of them interact, how do they behave?



Sending secret messages with synchronized chaos

A pair of synchronized chaotic circuits can be used to create a new kind of communication system. Moreover, a message becomes more private when it’s cloaked in chaos.

Dynamics of switching in charge-density waves

A charge-density wave is like a block of jello on a sticky plate. If you tug it sideways, it stays stuck in place … unless you tug it just hard enough; then it breaks loose and starts to slide. A coupled oscillator model showed that the sliding speed could depend discontinuously on the tugging force – as previously seen experimentally.

Synchronization of coupled oscillators

How can thousands of fireflies flash on and off in unison, all night long, without any leader or cue from the environment? More generally, how can dissimilar oscillators all come to act as one, in diverse biological, physical, and chemical systems? Over two decades of work on modeling such systems, using nonlinear dynamics, statistical physics, and computer simulations, has deepened our understanding of synchrony in our bodies and the world around us.   

Data analysis of human sleep and circadian rhythms

Studies of brave volunteers living for months in underground caves or windowless apartments have clarified how bright light shifts our circadian rhythms, why many of us like to take an afternoon nap, and why it's so hard to fall asleep two hours before your regular bedtime.

Topology of scroll waves

Spiral waves of activity occur in thin layers of heart muscle, nerve tissue, and certain chemical reactions. Scroll waves, their three-dimensional cousins, can be twisted, linked, and knotted according to a topological exclusion principle.

Topology of chromatin and supercoiled DNA

The linking number of DNA helps us unravel the structure of the chromatin fiber, the next level of coiling above the double helix and below the chromosome.