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How Long is a Second?

The Merriam-Webster Collegiate Dictionary says it is, "the 60th part of a minute of time : 1/86,400 part of the mean solar day; specifically : the base unit of time in the International System of Units that is equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom".

That's quite a mouthful, and many of your students may shrug their shoulders or roll their eyes as if to say, "Who cares?"  Well, they should!  Many conveniences we take for granted - like telephones, radio, and TV - depend on extremely precise timing in order to work in an acceptable way.  All of those electrons whizzing around at breathtaking speed bring us voices and images from afar.  Without exceptionally precise timing, some electrons would collide with each other keeping them from reaching their destinations - the appliances we place before our eyes and ears.  So, just as the need to keep trains from colliding led to the addition of the second hand to railroad engineers' watches in the 19th century (and the requirement that they set them each morning to the standard time shown on the clock at the entrance to their work yards), technological advances in the 20th century led to the need for atomic clocks.

Therefore, it may not surprise you to learn that, as precise as it seems, the current definition of a second is probably not precise enough for technological applications we will develop in the near future.  Hence, tools to measure time even more precisely are currently under development.  (If you want to follow the development of these new optical clocks, check this link to a Google search results page every once in awhile.  Here is an update I found from February 2010. And here is the link to an article on the next generation atomic clock, published in September 2014: http://spectrum.ieee.org/aerospace/satellites/introducing-the-worlds-most-precise-clock) In March 2006, Physicist Daniel Kleppner published a column in Physics Today exploring the future of the leap second and the physics of future advances in timekeeping technology.  It is titled, Time Too Good to Be True. On January 18, 2012, the New York Times reported that the nations of the world would meet on Thursday, January 19, to decide the fate of the leap second. You may read that article here: http://www.nytimes.com/2012/01/19/science/to-keep-or-kill-lowly-leap-second-focus-of-world-debate.html?hp

Of course, time is far from the only item requiring standards.  Without precise definitions for - and ways to accurately measure - gallons, inches, miles, etc., we'd be at the mercy of any crook smart enough to know how to pick our pockets without our knowledge.  Think about it.  When we go to the store to buy a gallon of milk, we trust that we're actually getting a gallon (or a pint, quart or half gallon).  Suppose a dishonest merchant decided to put a little bit less than a gallon in containers marked as holding a gallon.  If he sold enough, he'd do quite well.  The price per gallon we'd actually pay would be higher than the posted price, and most of us wouldn't even notice.  Over time, our crook could grow quite rich.  In case you think this sort of thing can't happen, read this New York Times article about a pharmacist who shorted people when he prepared prescriptions for cancer medication they bought from him.  (A free registration is required for access to the article.)

Anyway, abuses like this were among the things that led the US government to create the National Institute of Standards and Technology in 1901.  An absolutely riveting article appeared in The Washington Post to mark NIST's one hundredth anniversary. (The Washington Post article is also viewable online at http://www.lehigh.edu/~jph7/website/PictureGallery/A17404-2001Mar30.html ) If you decide to explore NIST's web site, be sure not to miss its:

Also take a look at The Why Files section, It's About Time.

On Sunday, October 16, 2005, the New York Times Week In Review section published an article on the changes in the way standards are being developed and maintained as technology advances.  Its author, Kenneth Chang, is especially good at clarifying why standards are necessary, and how time and technological advances have made the development of new standards necessary.  Don't miss the related slide show.

For related ideas, see the Classroomtools.com activities:


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original web posting: Sunday, May 12, 2002
last modified: Saturday, April 04, 2015