Friday, 17 February 2006

Murphy's Third Law

We quote 'Murphy's Law' all the time - which I tend to shorten to: what "can go wrong, will go wrong" (after Heinlein, 1980, p. ). Many of us probably think it arose with a Murphy lurking somewhere in Ireland.

And we would be wrong. We would be wrong on two counts.

Firstly, while known in the UK as Sod's Law, it is an American creation. According to an article in the Scientific American by Robert Matthews, it is named after Major Edward A Murphy Junior, a development engineer who worked in 1949 for a brief time on rocket sled experiments done by the US Air Force (1997).

The rocket sled project at Muroc Field (later renamed Edwards Air Force Base) tested human g-force tolerances during rapid deceleration, using a rail-mounted sled and a series of hydraulic brakes at the end of the track. While initial tests used a crash test dummy strapped to the sled's seat, subsequent tests were performed by Captain John Paul Stapp (Wikipedia, n.d.).

During the tests, questions were raised about the measurement accuracy of the instrumentation for the g-forces Captain Stapp was experiencing. Edward Murphy proposed using electronic strain gauges attached to the restraining clamps of Stapp's harness to measure the force exerted on them by his rapid deceleration. Murphy's assistant wired the harness, and a trial was run using a chimpanzee. The sensors provided a zero reading, however; it became apparent that they had been installed incorrectly, with each sensor wired backwards. It was at this point that Murphy made his pronouncement (Wikipedia, n.d.).

According to George Nichols, another engineer who was present, Murphy, in frustration, blamed the failure on his assistant, saying, "If that guy has any way of making a mistake, he will". Nichols' relates that "Murphy's law" then came about through the team members' subsequent conversation, and was condensed to "If it can happen, it will happen". This was named Murphy's Law by Nichols in mockery of what he perceived was Murphy's arrogance (Wikipedia, n.d.).

Others, including Edward Murphy's surviving son Robert, deny Nichols' account. Robert Murphy claims that his father's statement was "If there's more than one way to do a job, and one of those ways will result in disaster, then somebody will do it that way" (Wikipedia, n.d.).

In any case, the phrase first received public attention during a press conference in which Stapp was asked how it was that nobody had been severely injured during the rocket sled tests. Stapp replied that it was because they took Murphy's Law under consideration; he then summarised the law and said that in general, it meant that it was important to consider all the possibilities before doing a test (Wikipedia, n.d.).

Secondly, it is not a stand-alone law. As Edwin Cady (1965, p. 65) points out, what we term as 'Murphy's Law', is actually three laws:
  1. Nothing is as easy as it looks.
  2. Everything takes longer than you think it will.
  3. If anything can go wrong, it will. 
So, what "can go wrong, will go wrong" is actually Murphy's third Law.



  • Cady, Edwin H. (1965). IDEAtional Items: Murphy's Laws. Business Horizons, Winter 1965, Volume 8, issue 4 (pp. 65-66)
  • Matthews, Robert A. J. (1997). The Science of Murphy’s Law. Scientific American, April 1997, Volume 276, issue 4 (pp. 88-91)
  • Wikipedia (n.d.). Murphy's Law. Retrieved's_Law