## Pi Instant: March 14, 2015, at 9:26:53.58979... a.m.

The mathematical constant
pi
(or π)
represents the ratio of a circle's circumference to
its diameter. It is an extremely important value for geometry,
trigonometry, calculus, Fourier analysis, quantum mechanics, and so
much more. It has
no
exact rational or finite decimal form, but its
numerical value is approximately 3.1415926535897932385...
In honour of pi,
Pi Day
is celebrated each March 14, since "March 14" can be written as
"3/14" which comprises the first three digits of pi.
Pi Day in the year 2015 will be special, since
"March 14, 2015" could be written as "3/14/15", thus comprising the
first *five* digits of pi, not just three. Extending this,
some
have observed
that on March 14, 2015, at the time 9:26:53 a.m. (or
p.m.), the date and time could be written as "3/14/15; 9:26:53",
thus comprising the first *ten* digits of pi -- a "Pi Second".

I propose to take this idea a step further. The time 9:26:53 refers
to 26 minutes and 53 seconds after 9 o'clock. By extension, the
time 9:26:53.58979... refers to 26 minutes and 53.58979... seconds
after 9 o'clock. If the remaining (infinite) decimal expansion of
53.58979... is chosen to follow pi's digits exactly, then we obtain
a single precise instant, "3/14/15; 9:26:53.58979...", during which
*all* of the infinite digits of pi are all
represented by a single precise date and time.

I thus propose that March 14, 2015, at 9:26:53.58979... (i.e., at 26
minutes and 53.58979... seconds after 9 o'clock a.m., where
the remaining digits of 53.58979... all follow the digits of pi) be
designated and celebrated as Pi Instant, the single instant when all of
pi's infinite digits are all laid out before us.
Start planning your parties now!

-- Jeffrey S. Rosenthal, October 2014

(A slightly condensed version of this note was
published
in the February 2015 issue of
Math
Horizons;
see also a related radio interview.)

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