1.1. What is a social network?
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view. There are enough of these “long” edges that the total distance between
any two individuals, even at planetary scale, is a path of only length 6 or 7.
One easy way to reach someone far away in the world is to communicate to a
local government official, who typically has a connection to someone higher
in their government, and on to a country leader. Country leaders usually know
other country leaders, and so could pass the communication down on the other
side. Hierarchical structures are one way in which large networks can have
small diameters.
Interestingly, most social networks are not like this: the long connections are
not arranged in any careful way, but rather are present between many nodes,
distributed throughout, and these long edges connect to other nodes at all distances. In other words, the edges in any part of a social network are not a
careful mixture of mostly “short” edges and a few “long” edges, but instead
a much less structured mixture of edges of many lengths. From the perspective of any single individual, most, perhaps all of her edges will be short; but
some will be a bit longer, a few even longer than that, and perhaps one very
long. This connection structure is one example of a “small world” property:
the network looks qualitatively the same in a local neighborhood, in a region,
in a country, and for the whole world.
Thus the way to reach someone far away in the world is to find a close neighbor
with a long edge in the right direction. Milgram’s subjects tended to use this
strategy. If they had to send a package from, say, Denver to New York, they
would send it to someone they knew in the New York area, on the assumption
that the recipient would know someone in the right part of New York, and so
on.
• The number of connections an individual has (the number of relationships in
which s/he participates) is typically bounded above by a value between 125
and 150 that is known as Dunbar’s Number [30, 31]. This limitation appears
to be the result of cognitive limits on how many other individuals any one
person can keep track of in a meaningful way. This number matches very well
the number of individuals in traditional tribal groups, but seems to transfer
well to the online domain too.
Especially, but not exclusively, in the online domain, there are social networks
in which the relationships are weak, and it may be possible for an individual
to maintain a larger set of connections in such networks. For example, if the
relationships are such that they require almost no effort to maintain then an
individual can have many relationships. Heads of state have “relationships”
with most other heads of state in the sense that they could make a phone call
to them, but these relationships do not necessarily require much attention or
maintenance, which seems to be the constraint behind the Dunbar Number.
Similarly, many social media platforms allow users to have many “friends” or
followers who receive updates of their lives, but the amount of work to tell 5
people or 500 about some life event is the same, so again maintenance costs
3
view. There are enough of these “long” edges that the total distance between
any two individuals, even at planetary scale, is a path of only length 6 or 7.
One easy way to reach someone far away in the world is to communicate to a
local government official, who typically has a connection to someone higher
in their government, and on to a country leader. Country leaders usually know
other country leaders, and so could pass the communication down on the other
side. Hierarchical structures are one way in which large networks can have
small diameters.
Interestingly, most social networks are not like this: the long connections are
not arranged in any careful way, but rather are present between many nodes,
distributed throughout, and these long edges connect to other nodes at all distances. In other words, the edges in any part of a social network are not a
careful mixture of mostly “short” edges and a few “long” edges, but instead
a much less structured mixture of edges of many lengths. From the perspective of any single individual, most, perhaps all of her edges will be short; but
some will be a bit longer, a few even longer than that, and perhaps one very
long. This connection structure is one example of a “small world” property:
the network looks qualitatively the same in a local neighborhood, in a region,
in a country, and for the whole world.
Thus the way to reach someone far away in the world is to find a close neighbor
with a long edge in the right direction. Milgram’s subjects tended to use this
strategy. If they had to send a package from, say, Denver to New York, they
would send it to someone they knew in the New York area, on the assumption
that the recipient would know someone in the right part of New York, and so
on.
• The number of connections an individual has (the number of relationships in
which s/he participates) is typically bounded above by a value between 125
and 150 that is known as Dunbar’s Number [30, 31]. This limitation appears
to be the result of cognitive limits on how many other individuals any one
person can keep track of in a meaningful way. This number matches very well
the number of individuals in traditional tribal groups, but seems to transfer
well to the online domain too.
Especially, but not exclusively, in the online domain, there are social networks
in which the relationships are weak, and it may be possible for an individual
to maintain a larger set of connections in such networks. For example, if the
relationships are such that they require almost no effort to maintain then an
individual can have many relationships. Heads of state have “relationships”
with most other heads of state in the sense that they could make a phone call
to them, but these relationships do not necessarily require much attention or
maintenance, which seems to be the constraint behind the Dunbar Number.
Similarly, many social media platforms allow users to have many “friends” or
followers who receive updates of their lives, but the amount of work to tell 5
people or 500 about some life event is the same, so again maintenance costs