Hold out your palm and point it skyward. Every second about one muon will strike it. Muons are the most common remnant of cosmic ray collisions with the upper atmosphere that make it to sea level. They're responsible for some genetic mutations and even cancers, but the levels are low enough that we really don't have to think or worry about them much.
When I was about thirteen I came across a cosmic ray experiment near the summit of Sulphur Mountain in the Canadian Rockies. I've described the experience before - two young physicists had the patience to explain what they were doing to a kid. When comic rays collide with molecules in the upper atmosphere a lot of debris is produced - mostly in the form of subatomic particles. Some have very short lifetimes and don't make it far. Muons live long enough to make it down to sea level. But there's a twist. The half life of a muon is about two point two millionths of a second. Even if it traveled at the speed of light it would have traveled about six hundred and sixty meters. Most of these collisions take place a few tens of thousands of meters up. The trick is when we look at something moving very fast, time for it appears to run slowly. The number of muons making it to your hand is a manifestation that time is relative.
My mind was blown
People put up Stonehenge type markers in the prehistory to note seasons and other special dates. Moving closer to historical times a variety of sundials were developed. Clouds and night made them problematic and, depending on design and the skill of the observer, they were frequently only good to an hour or so. Even so the some Romans had no trouble complaining about them forcing a structure on life. The Romans moved a bit further timing devices in the form of water clocks and hour glasses. Water clocks were used to limit debate in the Roman Senate as well as arguments in legal proceedings. But time was still mostly for special occasions and localized. Most people relied on an approximate natural rhythm from cues from the sun and stars.
The thirteenth century saw the invention most associated with modern time. The mechanical escapement is a bit of cleverness that converts an oscillation into a ratcheted advancement in one direction. In a clock a pendulum's swing causes a gear to turn one notch at a time. The first use was in the church with pendulum driven bells to call the monks to prayer. Several decades went by and dials appeared allowing the visual estimation of time and a key driver of the Industrial Revolution had appeared a few hundred years early.
Since then mechanical time managed to penetrate deeper and deeper into society. The Industrial Revolution demanded workers at factories at certain hours. Home clocks were affordable to some households, but reliable alarm clocks were still expensive enough that the profession of the knocker-upper - someone you would hire to wake you up by a certain time - persisted in England until the twentieth century.
Now we have accurate portable time and increasingly an expectation to make use of our time. And now if clocks were limited to an accuracy of a second every century, much of our modern technology would no longer work. Sometimes it seems as if we're to be optimizing the time we have. We're admonished - or we admonish ourselves - against "wasting" time. For many being bored or having idle thoughts is somehow wrong.
Our sense time in our brain is very non-linear and irregular and an active area of study. Almost certainly there is no master clock. We seem to have individual interactions. I find I require a fair amount of idle time to daydream, think and make associations that don't seem to happen when I'm filling my time "slots." I can only be creative if I'm bored at some level.
When I began to work out of the home I made it a point to take a walk in the woods across the street every day I was around. You begin to notice the cycle of the seasons, and after a few years other patterns emerge. It's been about fifteen years now and the experience grows richer with time. Some of this Summer seems to echo with one eleven years ago and other parts seem unique. There are cycles for the trees, flowers, weeds, deer, wild turkeys, coyotes, bats, weasels and so much more. You experience some visually, some with sound and some at time and audio scales we normally don't notice (I often take along a microscope or a box that allows me to listen to ultrasound.)
Hold your arms out side to side. Imagine the distance from the furthest tips to be the age of the Earth - something like four point five billion years. Now take an emery file and take a few swipes from the fingernail that is touching the present. Now look at that fingernail. You've completely eliminated the period of human civilization.
I worry that humanity is failing the marshmallow test - where you give a little kid a marshmallow and tell him there will be two if he can save the one he has for wait for your return. Many key countries can't visualize the generation or two ahead to confront global warming. Perhaps we'd be better off if more of us moved a bit away from the forced regulation of our clocks and allowed more opportunity to consider the broader world.
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