GUESS

Yours
is as reliable
as the sun
rising in the east.

Mine
is as reliable
as a fountain
of cesium-133.

May the best clock win!

8/365

Musings

A figure skater spins faster as she brings her arms in close and slower as she lets them out. Planet Earth performs the same feat, speeding up or slowing down as its center of gravity shifts with tidal forces, sliding plates, and volcanic activity.

Our world also endures the drag of a relatively large moon constantly applying tidal brakes to our rotation. As a result, our days are lengthening, on average, while varying by unpredictable fractions of a millisecond.

The sun rises in the east each morning, but its timing isn't consistent or entirely predictable.

Exactly one second, by definition, will pass while you watch a cesium atom vibrate 9,192,631,770 times. These "cesium vibratory seconds" represent a vast improvement in accuracy over the previously used "counting Mississippis" standard.

Atomic clocks are so accurate, they need to adjust for the effects of gravity and special relativistic time dilation. A clock at the North Pole runs measurably faster than a clock at the equator, and faster at the top of a skyscraper than in the basement, varying the apparent length of a day with location and altitude.

As a result, when exactly an event takes place can depend on where you are when it happens.

Clocks don't display the time. They are all just guessing.

More Tomorrow.