DateTime Part 1: History of Time

16:04 Usefulness in Society

Timing of plantings, harvests, rainy seasons, river flooding was important for prehistoric cultures. It’s clear that at least some of the time that prehistoric humans did in fact base the alignment of structures on time.

“There’s a lot of woowoo crap around this.”

The ancients did use the north star to tell direction, but could do the same by the sun and other celestial objects with a rough idea of what time it was. Understanding of time helped defined social norms. People tended to cluster around the fire at night rather than wandering off.

19:10 Astrological

“They didn’t have a meeting at noon, it was eh be around here at mid day.”

Prehistoric understanding of time tended to be astrological in some manner, relying on the movements of planets, stars, or the moon. This is trickier than you think because of the way the earth actually moves in space.

School children are taught that the earth spins in space and goes around the sun, creating (respectively) the day and the year. Months were typically figured out based on the phases of the moon, which has a 28 day cycle. You’ll note that a year of lunar months doesn’t divide evenly into a year of 365 days.

“It’s like guidelines, like the pirate code.”

While the earth is going around the sun, so are the other planets, so predictions of where things are going to be are complicated. The Earth also wobbles on its axis, hence the procession of the equinoxes and the like. The point is, just looking up at the sky doesn’t give you a particularly good idea of time, at least not without a lot of extra work.

21:38 Time Value of Money.

If you borrow a dollar from me right now, it’s worth more than a dollar because I could have done something else with it in the meantime. This is true in the absence of inflation.

In the presence of inflation (or deflation), it gets more complicated. Tying value to money is one of the things that make this complicated. To be incentivized to take the risk of lending, there has to be an upside, hence interest. However, that upside has to be carefully balanced against risk of total loss.

23:06 Granular Understanding

This was based upon astrological positioning. They paid careful attention to a dozen or so constellations and how they moved around the sky and how things in the sky moved around them.

“It’s also where we get phrases like “the dog days of summer” because that’s when the star Sirius, one of my favorite stars, rises over the horizon at about the same time as the sun.”

This is where we get our modern zodiac. As the twelve constellations of the zodiac move around. We probably got our concept of hours and days from the Egyptians

24:15 Taxes

“The bane of all existence”

The Egyptians levied taxes every other year, but still devised a calendar of 365 days, having four seasons, primarily so that they could predict the flooding of the Nile.

25:00 Warfare

The opportune time for picking fights with the neighbors also depended a lot on being accurate with time, as the troops had to be home for harvest.

25:45 Measuring Time

Time was measured by the position of the sun, or in some cases rather ingenious clocks (roman water clocks, sundials, etc.).

26:27 Commercial and Industrial Processes

Commercial processes got more complicated and time-bound due to scaling out. Longer sea voyages required accurate time-keeping in order to figure out longitude. Industrial processes started requiring more accurate measurement of time and distance as well.

29:10 Significant Changes

Significant changes in social norms around time. More people start to be employees rather than working for themselves. More people lived in urban centers as well.

“It went from you work until you can’t work anymore because…to you work these hours then go home to your family.”

Significant increases in travel speed and reliability, meaning that people do schedule things more tightly because they can. People actually started traveling fast enough and communicating fast enough that things like time zones started having to be used

33:45 Daylight Savings Time (DST)

Energy use during war (and energy use considerations in general) caused DST to be implemented, starting in Canada in 1908 and introduced in 1918 in the US during the tail end of WWI.

35:15 Measuring Time

Time was typically measured with mechanical clocks by the end of this period.

35:45 Machine Timings in Factories

Odds are good that if it comes off a machine, the machine is timed to do certain things on a repeating basis. The accuracy of that clock impacts how many goods can be produced, and to what degree of quality.

37:45 Global Positioning System (GPS)

“I remember it telling me to drive into a lake.”

Accurate time management is essential for accurate GPS readings, as the time it takes for signals to arrive from multiple satellites is how distance is calculated, which ultimately leads to position. Light travels 30 centimeters in one nanosecond, or a meter in 3 and a third nanoseconds.

“You know what the military does…they just put more explosives on it.”

GPS, in turn, is used to guide missiles and airplanes to their destinations, as well as for calculating the costs and timelines for shipping goods. Being off by one-billionth of one second will create one foot of inaccuracy.

41:21 Science and Computers

“I know Kerberos does this under the hood.”

Many authentication protocols have a time component to them to avoid replay attacks. That is, your key is only good for a short period of time, after which you have to get a new one (in case someone else gets it).

“There’s actually a fair amount of inaccuracy in those pumps.”

Extremely accurate measurement for scientific and manufacturing applications. This includes everything from laser measurements of distance, to measuring volume of fluids going through a pipe (think of filling up your car).

44:35 Measuring Time

Time is typically measured using Caesium 133 atoms in an atomic clock. Then some sort of clock is used locally (quart oscillators) that is lower accuracy, which is then synchronized with a more accurate and expensive clock elsewhere. Your calendar, no matter how complex, is several orders of magnitude less dependent on extremely accurate time operations than pretty much all the rest of civilization.