HOW-OF-WHY

DISASTERULES
by Michael John Moynihan © 2005 all rights reserved



Edward A. Murphy was born in 1918 and died in 1990. During the late
1940s, Edward was a research and development officer at
Wright-Patterson Air Force Base in Dayton, Ohio. In 1949, he was
involved in Air Force Project MX981.

It was at this time that Edward set up measuring devices to investigate
the effects of rapid deceleration of human beings. The point of this
was to attempt to find out how very much sudden deceleration a person
can stand in a crash. A human test subject was strapped to a "sled"
that could accelerate to very rapid speeds and then decelerate very,
very quickly. Edward devised a harness to hold the human guinea pig in
place during the tests.

To record the effects on the volunteers who took part, Edward Murphy
devised a harness carrying strain gauges to measure the gravitational
forces generated in each test run. During one run, everything seemed to
go well. But the harness had failed to record any data at all. Edward
was called in, and discovered that each and every single strain gauge
had been wired incorrectly. Upon discovering the problem, Murphy cursed
the technician responsible and said, "If there is any way to do it
wrong, he'll find it."

After rewiring the gauges told his colleagues that this highlighted a
very important rule that all engineers should keep in mind: "If there are two ways of doing something, and one of them can lead to
disaster, you should assume that's the way it will be done."

The MX981 project manager kept a list of "laws" and added this one, which he then named "Murphy's Law".

Soon afterwards, Dr. John Paul Stapp, who rode a sled on the
deceleration test to a stop, experiencing 40 Gs, held a press
conference. He said that the positive safety record on the project was
due to a firm belief in "Murphy's Law" and in the necessity to try and
circumvent it. A reporter misquoted Murphy's Law and as it was repeated
and repeated it morphed into the truism that we know today, about life
in general:

"If something can go wrong, it will go wrong".

But that was just the beginning. Many scientists regard it as nonsense.
But one who doesn't is Robert Matthews. Since the mid-1990s, he has
discovered that many cases of Murphy's Law really can be explained by
serious "scientific" principles. One such example (and you can test this at home): Toast usually lands
on the floor butter-side down. But according to Matthews, there are
many other examples of Murphy's Law at work in our universe.

Have you ever wondered why the supermarket checkout line you're
standing in so often moves slower than the one next to you? Or why the
place you're looking for in an atlas is so often on the difficult to
see part of the map? Or why string or rope ties itself in knots most of
the time?

Take that case of the supermarket checkout line. Why does the one we
pick so often move slower than the one next to us? Robert explains, if
we pick a longest line, or one with a family of 7 shopping for the
winter, then it's not hard to see why your line will be slow. But, says
Robert, scientists insist that on the average all the lines are as
likely to move at the same rate as any other, so there just can't be a
"Murphy's Law of Supermarket Checkout Lines": That if your line can be
can move slowest, it will.

"The trouble with this argument is that on any one visit to the
supermarket, we don't care about 'the average' ", says Robert, "We just
want our line to be the fastest on that particular occasion. And if
there are X lines, the chances that we've picked the fastest-moving one
on that trip is just 1/X "So�, explains Robert, �this holds the key to
the reality of Murphy's Law of Supermarket Checkout Lines: "When we
line up, there are three lines we care about: the one we're in, plus
the two lines to either side. So the chances our line will move faster
than both our neighboring lines is just 1 in 3. Therefore, in almost 70
per cent of trips to the supermarket, Murphy's Law will prove correct,
and one or other of the lines next to us will be faster than ours !"

And why is it that when we're using a road atlas, the place we want so
often turns up on the difficult to see part of the map, down the
central crease or on the edge ? The answer, he says, is that although
those "difficult to see parts" don't seem very wide, they track the
total perimeter of the map - and simple geometry shows they actually
take up over 50 per cent of its total area. So a location picked at
random in an atlas has a 50/50 chance of turning up in the map's
difficult "Murphy Zone".

Why string and rope gets knotted so easily is the subject of �Knotted
rope: a topological example of Murphy's Law� in a issue of Mathematics
Today. It can be found on the internet at:

http://ourworld.compuserve.com/homepages/rajm/knotfull.htm

My own variation of Murphy's Law�
If something can go wring, it probably already has,
and will not be discovered until it is too late.

Oh, and most people will not care about it.