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It's 2008, and we're in a factory in Hungary.

A huge clattering machine takes in finely ground clay and sand

and sends out patches of freshly pressed floor tiles

ready to be blasted in the kiln. A few metres away stands a smartly

dressed man, neat beard, thick glasses and a clipboard. Beside him, the production supervisor is answering

his questions with a quizzical expression on his face. The tile company is in trouble,

and the man with a clipboard is here to help.

But the questions he's asking seem trivial, silly even.

Who here are you friends with?

Who do you chat to about work?

What, the supervisor wonders,

does any of this have to do with tiles?

Over on the other side of the globe, it's a pleasant day in Walton Hills, Ohio, and high-voltage

power line has started sagging, just a little, relaxing in the warm sun. Beside it, the branches of a North American beach stretched

out with confidence into the surrounding space, gently swaying in the summer breeze. And then,

at 2.02pm on August the 14th, the power line and the branch meet. 345,000 volts surged down through the tree and into the earth, a fuse trips, and instantly the

stretch of line is triggered into shutdown.

It's just one small fault in a huge, sprawling power grid,

but this is the first in a cascade of events

that will soon bring chaos and confusion to millions.

I'm Hannah Fry, a mathematician who studies patterns in human behaviour.

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