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Time machines might
only be available in the movies, yet many people have experienced
unexplained events that seem to be temporary but very real slips
into the past and the future. |
Every once in awhile,
time seems to go haywire, gets fouled up in a glitch, moves
impossibly fast or impossibly slow. Is it time itself that gets
screwed up? Or is it just our perception of it? |
Time's Origins
Webster's New World College Dictionary (Fourth Ed.) defines time as:
II. a period or interval. 1: the period between two events or during
which something exists, happens or acts; measured or measurable
interval
At its core, time is fairly elusive. We can't see it or sense it --
it just happens. Human beings have therefore come up with ways to
measure time that are totally arbitrary and also fairly interesting
from a historical perspective.
The day is an obvious starting point for time. A day consists of a
period of sunlight followed by night. Our bodies are tuned in to
this cycle through sleep, so each morning we wake up to a new day.
No matter how primitive the culture, the concept of a day arises as
an obvious and natural increment.
We use clocks to divide the day into smaller increments. We use
calendars to group days together into larger increments. Both of
these systems have very interesting origins that we'll find out
about in the course of this article. |
Measuring Time
The measurement of time covers an incredible range. Here are some
common time spans, from the shortest to the longest.
- 1 picosecond
(one-trillionth of a second) - This is about the shortest period
of time we can currently measure accurately.
- 1 nanosecond
(one-billionth of a second) - 2 to 4 nanoseconds is the length
of time that a typical home computer spends executing one
software instruction.
- 1 microsecond
(one-millionth of a second)
- 1 millisecond
(one-thousandth of a second) - This is the typical fastest time
for the exposure of film in a normal camera. A picture taken in
1/1,000th of a second will usually stop all human motion.
- 1 centisecond
(one-hundredth of a second) - The length of time it takes for a
stroke of lightning to strike
- 1 decisecond
(one-tenth of a second) - A blink of an eye
- 1 second - An
average person's heart beats once each second.
- 60 seconds -
One minute; a long commercial
- 2 minutes -
About as long as a person can hold his or her breath
- 5 minutes -
About as long as anyone can stand waiting at a red light
- 60 minutes -
An hour; about as long as a person can sit in a classroom
without glazing over
- 8 hours - The
typical workday in the United States, as well as the typical
amount of sleep a person needs every night
- 24 hours - One
day; the amount of time it takes for the planet Earth to rotate
one time on its axis
- 7 days - One
week
- 40 days -
About the longest a person can survive without food
- 365.24 days -
One year; the amount of time it takes for the planet Earth to
complete one orbit around the sun
- 10 years - One
decade
- 75 years - The
typical life span for a human being
- 5,000 years -
The span of recorded history
- 50,000 years -
The length of time Homo sapiens has existed as a species
- 65 million
years - The length of time dinosaurs have been extinct
- 200 million
years - The length of time mammals have existed
- 3.5 to 4
billion years - The length of time that life has existed on
Earth
- 4.5 billion
years - The age of planet Earth
- 10 to 15
billion years - The suspected age of the universe since the big
bang
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