2014-04-26 10:52:28 -04:00
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phase of the moon
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2014-04-26 11:54:15 -04:00
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n. Used humorously as a random parameter on which something is said to
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depend. Sometimes implies unreliability of whatever is dependent, or that
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reliability seems to be dependent on conditions nobody has been able to
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determine. This feature depends on having the channel open in mumble mode,
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having the foo switch set, and on the phase of the moon. See also heisenbug.
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True story: Once upon a time there was a program bug that really did depend
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on the phase of the moon. There was a little subroutine that had
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traditionally been used in various programs at MIT to calculate an
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approximation to the moon's true phase. GLS incorporated this routine into a
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LISP program that, when it wrote out a file, would print a timestamp line
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almost 80 characters long. Very occasionally the first line of the message
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would be too long and would overflow onto the next line, and when the file
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was later read back in the program would barf. The length of the first line
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depended on both the precise date and time and the length of the phase
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specification when the timestamp was printed, and so the bug literally
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depended on the phase of the moon! The first paper edition of the Jargon
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File (Steele-1983) included an example of one of the timestamp lines that
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exhibited this bug, but the typesetter corrected it. This has since been
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described as the phase-of-the-moon-bug bug. However, beware of assumptions.
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A few years ago, engineers of CERN (European Center for Nuclear Research)
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were baffled by some errors in experiments conducted with the LEP particle
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accelerator. As the formidable amount of data generated by such devices is
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heavily processed by computers before being seen by humans, many people
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suggested the software was somehow sensitive to the phase of the moon. A few
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desperate engineers discovered the truth; the error turned out to be the
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result of a tiny change in the geometry of the 27km circumference ring,
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physically caused by the deformation of the Earth by the passage of the
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Moon! This story has entered physics folklore as a Newtonian vengeance on
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particle physics and as an example of the relevance of the simplest and
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oldest physical laws to the most modern science.
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