Time talk

time/time.md

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+#!/bin/env slides
+
+# Time
+
+![sxiv -sf -f](time.webp)
+
+I'm Bruce and this is a talk about time.
+
+--------------------------------
+
+# Time Is a Social Construct
+
+![sxiv -sf -f](in-time.webp)
+
+I'm gonna be talking about years and hours and
+minutes and days and stuff.
+
+Turns out time is pretty weird, and not a
+real thing that exists in the universe.
+
+Mostly this is just gonna be a bunch of
+fun facts about the history of time.
+
+---------------------------------
+
+# In the Beginning
+
+Since the dawn of time, time was dawn.
+
+People used day/night cycles and seasonal
+variations to keep track of the passage of time.
+
+---------------------------------
+
+# Hours
+
+In ancient Egypt, they thought the constellation
+**Sirius** was cool because it could be used to
+predict the flooding of the Nile (very important).
+
+Sirius has **12 stars**, so the Egyptians thought
+it was a cool timey number and divided the night
+into 12 intervals.
+
+Everyone else in the wider region copied them
+(Babylonians, Greeks, Romans, etc.)
+
+---------------------------------
+
+# Unequal Hours
+
+Originally, there were 12 hours of daytime
+and 12 hours of nighttime.
+
+If you lived near the equator, this works pretty well.
+
+If you don't, it means that a winter daytime
+hour is shorter than a summer daytime hour.
+
+Where I grew up (Seattle), this means that
+an hour would be:
+
+- **42 minutes** long on December 21 during the day
+- **80 minutes** long on June 21 during the day
+
+---------------------------------
+
+# Unequal Hours
+
+## Downsides
+
+- The same thing takes a different number of hours
+  in different seasons.
+- Need to think about what season it is.
+
+## Upsides
+
+- Easy to measure with a sundial.
+- Kinda useful to talk about fractions of
+  available daylight time.
+- No one wants to do anything during winter,
+  so the hours are correspondingly wimpy.
+- Very human.
+
+---------------------------------
+
+# Minutes and Seconds
+
+- Invented in the Islamic golden age
+- First **minute** division of an hour
+- **Second** minute division of an hour
+- 60 is a cool number (thanks Sumerians)
+  - Is divisible by 2, 3, 4, 5, 6, 10, 12, 15, 20, 30
+
+---------------------------------
+
+# Calendars Are Hard
+
+People historically kept track of the seasons using
+an awkward combination of lunar cycles and solar
+cycles, which was complicated and kept drifting out
+of sync (not an even number of moon cycles in a year).
+
+- **Julius Caesar** was a **pontifex**
+  - Good for electoral shenanigans
+  - But had to perform a religious ceremony to adjust the calendar
+  - Too busy doing imperialism to bother adjusting the calendar
+  - Got way out of sync
+  - Invented the **Julian Calendar** to get out of the job
+    - Solar calendar, so no drift
+- Later **Pope Gregory** adjusted the calendar
+  - The "**Gregorian Calendar**"
+
+---------------------------------
+
+# Weeks
+
+- 7 days because, uh, 7 celestial bodies I guess?
+  - Sun, moon, 5 other planets
+- Days of the week named for the celestial bodies:
+  - Saturn day
+  - Sun day
+  - Moon day
+- Then the Norse got involved somehow
+  - Tyr's day
+  - Wotan's day (Odin)
+  - Thor's day
+  - Frigg's day (gotta get down on Frigg's day)
+
+---------------------------------
+
+# Astronomy Sucks as a Clock
+
+Very sloppy, filing a bug report now:
+
+- Can't tell time when it's cloudy
+- Daylight hours change seasonally
+- Latitude and longitude
+  - Earth wobbles, so latitude and longitude are also bullshit
+  - Continental drift
+- Not an integer number of lunar cycles in a year
+- Not an integer number of days in a year
+- 365.2422 is a lame number (not easily divisible)
+- Drifts over time because we live in a fallen world
+
+---------------------------------
+
+# We Can Make Better Clocks
+
+I mean, not at first. Old clocks sucked.
+
+- Water clocks
+  - Dripping in a bucket at constant-ish time
+- Candle clocks
+  - Put nails in the side of the candle to loudly fall out
+
+---------------------------------
+
+# Imperialism and Capitalism
+
+Two of the main driving forces for making better clocks
+were imperialism and capitalism (name a more iconic duo)
+
+## Imperialism
+
+- How do we keep time across a world-spanning empire?
+- How do you know how far you are across the ocean
+  with no landmarks?
+
+## Capitalism
+
+- How do you make workers show up on time?
+- How do you make workers work longer?
+- How do you keep a train schedule between cities?
+
+---------------------------------
+
+# Time Zones
+
+Once trains got fast enough, you'd actually notice
+time differences between cities.
+
+Every city ran on **local solar time.**
+
+Railroads hated it, so they pushed for the adoption
+of hour-bracketed **time zones.**
+
+Synced up with **Greenwich Observatory** as the standard time.
+
+---------------------------------
+
+# Time Balls
+
+![sxiv -sf -f](time-ball.webp)
+
+Greenwich Observatory had a **time ball** that they dropped
+at exactly 1pm.
+
+Ships saw it drop and set their clocks accordingly.
+
+Some random guy saw one and thought it would be a cool party
+event for the NYT opening a new HQ in Times Square in 1905.
+
+---------------------------------
+
+# Clocks and Watches
+
+Invented for navigation and religious purposes,
+repurposed for industrial factories.
+
+Previously people came in to work when the sun
+came up, left when the sun went down.
+
+Factory owners introduced clocks to remove all
+slack from their workers' lives.
+
+Major labor clashes over workers being fired
+for not arriving at exactly the right time,
+but also factory owners cheating the clock.
+
+Workers forbidden from having their own watches.
+
+---------------------------------
+
+# What Is Time?
+
+Once clocks started getting accurate, it raised
+the question: "what is a second?"
+
+**Not:** 1/(12 * 60 * 60)th of a day
+
+Earth's rotation changes (tidal deceleration).
+
+The French standardized the definition of a second:
+
+- Originally based on an **average** day length
+- Then based on the year length of 1900 (?!) "ephemeris second"
+- Then bombarding ammonia with radiation till it radiates
+- Then caesium radiation frequency (atomic clocks)
+- In 2022, redefined to use optical clocks
+
+---------------------------------
+
+# Problems for the Future
+
+Oh god, there's relativity too.
+
+- Synchronizing time across planets is hard
+- Time is subjective
+- Time dilation
+  - Your time is not my time.
+- Relativity of simultaneity
+  - What even is "now"?
+
+I give up.
+
+---------------------------------
+
+# Time's Up
+
+Okay I'm done.