Fragile networks:
An article (Catastrophic Cascade of Failures in Interdependant Networks, Sergey B. Buldyrev et al, NATURE vol. 565. no. 7291 April 15, 2010 page 1025 has highlighted a difficulty in networks.  They tend to go all together when they go.

Decades ago I was in Boston during the Great Northeast Blackout.  Years later I met someone who said cheerfully, “I am a blackout baby.”  The power failed for some time, and lacking much else to do, many people engaged in social activity that resulted in a conspicuous birth spike nine months later.  So if you want babies, cut the power off. 

As I remember it was like this.  If you take a metal plate, very smooth, and place it face to face with a similar plate and then put a positive charge on one plate and a negative charge on the other you can store a little bit of electrical charge in the system.  The amount is not much, but the charge can be delivered instantly and efficiently so the resulting condenser or capacitor has a great number of uses in electronics.  If you hang a cable from poles and put an enormous amount of charge on it, it will store some charge by its capacitance with the ground below.  The amount is again not all that much, but with alternating current, where the charge reverses direction rapidly there is a tiny current induced in the ground.  The result is that the ground absorbs some energy so that alternating current is not an efficient way of carrying power over very long distances.  Tens of miles, sure.  Hundreds of miles, maybe.  Thousands of miles is right out of the question. 

Given an enormous number of cables stretched over an entire region like the Northeastern Unite States, the amount of charge that is stored in the system is very substantial.  Lake Erie of course flows over Niagara Falls on its way to the sea.  Most of the water is drawn off for power generation with only a fairly thin veil left for the tourists.  The Niagara power station puts out a lot of electricity.  Now a power grid consists of a large number of power stations putting out electricity and a widely distributed network of users tying into it.  If one power station fails, electricity comes in from the grid as all nearby stations shoulder more of the load, and although it is less efficient to bring in the power from a distance the local consumers get their power pretty much uninterrupted. 

Well something went wrong at Niagara.  But instead of the local safety reflexes cutting it out of the grid at once, somehow this enormous wad of energy went all the way around Lake Erie, throwing circuit breakers all the way.  With the resulting great hole in the grid, the stations on the circumference tried to supply the needs, overloaded an shut down.  And this resulted in a wave that swept all the way across the Northeast.  I was studying and wishing I were elsewhere.  When the lamp flickered I thought, “Go out.  Go out.”  I got my evening off.  I wish I had saved the wish for something more socially beneficial. 

At least that is how my engineering friend explained it to me.  I thought that the power grid was at that time the most complex system that had ever been built, rivaling a brain.  Then like a brain it had become conscious, contemplated reality for a moment and then committed suicide.  Dumb ideas are of course a specialty. 

Over the next few days the authorities explained that it was the interconnectedness of the grid that had been its downfall and that what was needed was more interconnectedness.  It seemed strange at the time.

Now decades later it is realized that a complex densely interconnected system is indeed subject to catastrophic failure.

So if there is a system you can’t afford to lose, you must have a backup system.  Anybody who shoots rapids with a canoe knows that you must never ever go out with fewer than three canoes.  That’s so when you destroy one the other two can hold everybody.  All right, I used to go out for days at a time shooting rapids alone.  See remark above about dumb ideas.

We live in a world in which we seem bewitched by the Big System.  We have a global economy, a global set of laws and global ideas of human rights and social propriety.  But these are things we cannot afford to lose.  Why in the world would we not have backup systems.  The most basic prudence mandates separate units, one sure when another fails.

Evolution this time is a lot smarter.  Animals are sequestered in small mostly isolated populations.  This is an obvious but poorly worked out basic law of biology.  If you go for the big system it will fail ultimately.  And it will fail very soon because evolution has been at pains to make it fail forestalling a worse catastrophe later.

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