Another year has come and gone. During the last year, we celebrated anniversaries, holidays, and birthdays. We do this to mark the time, and give ourselves a sense of perspective. We mark the seasons, the height of our children as they grow older, and rites of passage. We want to know where we have been and where we are going.
The year is 2019. That is supposed to mark 2,019 years since the life of Christ, a man whom no one alive today can know for sure existed. Yet we use the birth and death of that person as a reference for keeping time. According to the Hebrew Calendar, the year is 5779, and they used a different starting time to arrive at that number of years.
1752 (MDCCLII) was a leap year starting on Saturday of the Gregorian calendar and a leap year starting on Wednesday of the Julian calendar, the 1752nd year of the Common Era (CE) and Anno Domini (AD) designations, the 752nd year of the 2nd millennium, the 52nd year of the 18th century, and the 3rd year of the 1750s decade. As of the start of 1752, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923. In the British Empire, it was the only year with 355 days, as 3–13 September were skipped when the Empire adopted the Gregorian calendar.
In just that passage alone, we can see how many adjustments were made to keep the calendar in sync with the sun and the seasons. A year is actually 365.2422 days, depending on the measure you use. To make up for that difference we insert leap years into our calendars to keep our calendars in sync with the seasons.
Delving a little deeper, we also learn that a “day” is not exactly 24 hours (from Wikipedia):
A day, understood as the span of time it takes for the Earth to make one entire rotation with respect to the celestial background or a distant star (assumed to be fixed), is called a stellar day. This period of rotation is about 4 minutes less than 24 hours (23 hours 56 minutes and 4.1 seconds) and there are about 366.2422 stellar days in one mean tropical year (one stellar day more than the number of solar days). Other planets and moons have stellar and solar days of different lengths from Earth’s.
Notice all of the qualifications used, and that other planets and moons have different stellar days. Our earth travels around the sun in a slightly elliptical orbit, meaning that it is traveling faster or slower depending on the position of the earth in orbit with the sun. The earth rotates on an axis inclined by 23 degrees, giving us the seasons, and perhaps adding to some confusion.
Add to all of that, that our solar system is moving in orbit around the core of our galaxy, the Milky Way, and then we really begin to get a sense that nothing is fixed in time. Everything is in flux, but we measure time to give ourselves a frame of reference so that we can work together. So that we can meet at a specified time. So that we can create contracts of agreement to get things done.
According to Wikipedia, in 1960, a day was defined in terms of the period of the orbital motion of the Earth around the sun in the year 1900. Since then we’ve built atom clocks with greater and greater accuracy. I have been loosely following improvements in precision of these and other clocks for the last decade and I have to say, the progress is rather astonishing.
In 2011, the National Institute of Standards introduced the most precise atomic clock that would neither lose or gain a second in 138 million years. Then in 2014, they doubled that record to 300 million years. In 2013, an optical lattice clock (I don’t understand it either — but I’m floored) was demonstrated with an accuracy (as far as they could measure) of 1 second in 15 billion years or, the age of the Universe.
The clocks they are building now are so accurate that they can measure time dilation from gravity on earth simply by changing elevation. Huh. I thought that time only dilates in staff meetings…
So in a sense, everything is relative to our perspective. Like language, we invented time so that we can collaborate, to work together. Time is an abstraction we use to compartmentalize our experiences, so that we can corroborate our experience with others and so that we can take stock of our achievements.
No other animal is this interested in time. The human interest in time is a result of one skill that is baked into our genes: collaboration. That skill can be our downfall or our genius, depending on how we choose to use our time.