“ The iPS cell phenomenon is so new and so hyped up that it’s good we’re taking a step back to ask what they can really do. ” — chad tang, page 13
In the News
a few master
switches can
rule a network
Social sites like Facebook
especially easy to control
STORY ONE
By Rachel ehrenberg
It’s like a Hollywood political thriller come true: A handful of people lurk- ing in the shadows control the minds of millions. New research reveals
that it’s possible for a few individuals to
enslave an entire network, even if they
aren’t highly connected themselves.
Scientists have figured out how to
identify the nodes (points that link to
other points in a network) that when
t weaked can influence an entire network.
The research, published in the May 12
Nature, might lead to more secure power
grids, tricks for controlling the metabolic
processes of cells and marketing campaigns that spread like the plague.
If you wanted to nudge people on a
social network into trying a new product
or get a biochemical system to turn compound A into compound B, you could just
push your product or compound into
every entry point in the network. But
that’s sort of a silly approach, says study
coauthor Jean-Jacques Slotine of MIT.
A much more efficient tactic would be to
target just the nodes needed to get the
desired outcome.
So, along with colleagues Albert-László
Barabási and Yang-Yu Liu of Northeastern
University in Boston, Slotine developed
an algorithm that calculates the minimum
a new algorithm identifies the subset of nodes that must be manipulated in order
to dominate a network. In this illustration, exerting control requires interfering with
a handful of “driver nodes,” in blue. dense networks are generally easier to control.
number of these driver nodes and finds
them. Then the researchers asked how
much this minimum number depends on
the architecture of the network (be it a
tidy grid or a convoluted web) and its connectivity (whether each node is linked to a
lot of other nodes or just a few).
Oddly, a network’s shape barely matters. The number of nodes needed to
control a whole network mostly depends
on the average number of connections
per node, the researchers found. Sparse
networks, such as the regulatory system
controlling genes in a yeast cell, are pretty
resistant to control; roughly 80 percent
of the nodes need to be influenced to get
the desired outcome. Dense networks,
on the other hand, such as many social
networks like Facebook, are much
easier to control: Influence roughly
20 percent of the nodes and the whole
network responds.
“I found that very shocking,” says
Magnus Egerstedt, director of the Geor-
gia Robotics and Intelligent Systems
Laboratory at Georgia Tech. “Social
networks, which seem to be these ran-
dom, ad hoc collections of people freely
expressing information and sharing
their thoughts — those were much easier
to control than other networks.”
Another counterintuitive finding had
to do with where those power nodes lie.
The nodes to tweak aren’t the hubs with
many, many connections, but unassum-
ing nodes off to the side.
