Just How Long Ago Was the Civil War?

I heard a story on All Things Considered this afternoon about a book that was returned to Washington and Lee University in Virginia, 145 years after it was stolen. Let’s see 2009-145 = 1864. That’s nearing the end of the American Civil War. The Battle of Gettysburg took place July 1-3 of 1863. The South surrendered at Appomattox on April 9, 1865. Washington and Lee University is located in Lexington, VA near the western border of Virginia.

What impressed me about the story was that the book had been in the same family for three generations. The grandson of the Union soldier who stole the book in 1864 died recently and gave the book to a friend who returned it to the library. The reporter didn’t mention how recently the grandson had died but it’s still amazes me that the Civil War could be so close in someone’s memory.

Perhaps this is part of the reason why grudges, once they get started, can last so long. Suppose that Union soldier told his grandson to hate or distrust the South. One hundred plus years later and the hatred might still be tended.

It also reminds me of an extended figure used by Alvin Toffler at the start of “Future Shock”. I remember him estimating that there were only 800 generations of human civilization between the present and the invention of agriculture. That number isn’t very large but the changes that have occurred are immense.

It’s interesting how shifting the units of measurement changes our perceptions of distance. So 2000 years, 20 centuries, and 2 millenia are all the same length of time but each of them connotes or feels slightly different. If a generation last 30 years then there are 66 generations between now and the beginning of the Christian era.

When you get beyond human scale it is even more difficult to understand units. When reading professional literature in astronomy or geology you often see references to gigayears - a billion years - and myr for millions of years.

Wikipedia says the preferred ISO 31-1 usage is Ma for a mega annum.

The more you dig into it the more complicated the business of standards becomes. NIST - the National Institute of Standards - has an entire book on the conventions used in the international system of units.

Here is what it says about the basic unit of time - the second:

The unit of time, the second, was at one time considered to be the fraction 186 400

of the mean solar day. The exact definition of “mean solar day” was left to the

astronomers. However measurements showed that irregularities in the rotation of the

Earth made this an unsatisfactory definition. In order to define the unit of time more

precisely, the 11th CGPM (1960, Resolution 9; CR, 86) adopted a definition given

by the International Astronomical Union based on the tropical year 1900.

Experimental work, however, had already shown that an atomic standard of time,

based on a transition between two energy levels of an atom or a molecule, could be

realized and reproduced much more accurately. Considering that a very precise

definition of the unit of time is indispensable for science and technology, the 13th

CGPM (196768, Resolution 1; CR, 103 and Metrologia, 1968, 4, 43) replaced the

definition of the second by the following:

_The second is 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._

It follows that the hyperfine splitting in the ground state of the cesium 133 atom is

exactly 9 192 631 770 hertz, ν(133Cs)hfs = 9 192 631 770 Hz.

At its 1997 meeting the CIPM affirmed that:

This definition refers to a cesium atom at rest at a temperature of 0 K.

This note was intended to make it clear that the definition of the SI second is based

on a cesium atom unperturbed by black body radiation, that is, in an environment

whose thermodynamic temperature is 0 K. The frequencies of all primary frequency

standards should therefore be corrected for the shift due to ambient radiation, as

stated at the meeting of the Consultative Committee for Time and Frequency in

1999.