ATTOSECOND
(A billionth of a billionth of a second.) The most fleeting events that scientists can clock are measured in attoseconds. Researchers have created light pulses lasting just 53 attoseconds using high-speed lasers. Although the interval seems unimaginably brief, it is an aeon compared with the Planck time—about 10–43 second—which is believed to be the shortest possible duration.
FEMTOSECOND
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(A millionth of a billionth of a second.) An atom in a molecule typically completes a single vibration in 10 to 100 femtoseconds. Even fast chemical reactions generally take hundreds of femtoseconds to complete. The interaction of light with pigments in the retina—the process that allows vision—takes about 200 femtoseconds.
PICOSECOND
(A thousandth of a billionth of a second.) The bottom quark, a rare subatomic particle created in high-energy accelerators, lasts for one picosecond before decaying. The average lifetime of a hydrogen bond between water molecules at room temperature is three picoseconds.
NANOSECOND
(A billionth of a second.) A beam of light shining through a vacuum will travel only 30 centimeters (not quite one foot) in this time. The microprocessor inside a personal computer will take less than a nanosecond to execute a single instruction, such as adding two numbers. The K meson, another rare subatomic particle, has a lifetime of 12 nanoseconds.
MICROSECOND
(A millionth of a second.) That beam of light will now have traveled 300 meters, about the length of three football fields, but a sound wave at sea level will have propagated only one third of a millimeter. The flash of a high-speed commercial stroboscope lasts about one microsecond. It takes 24 microseconds for a stick of dynamite to explode after its fuse has burned down.
MILLISECOND
(A thousandth of a second.) The shortest exposure time in a cell-phone camera. A housefly flaps its wings once every three milliseconds; a honeybee does the same once every five milliseconds. The moon travels around Earth two milliseconds more slowly each year as its orbit gradually widens. In computer science, an interval of 10 milliseconds is known as a jiffy.
TENTH OF A SECOND
The duration of the fabled “blink of an eye.” The human ear needs this much time to discriminate an echo from the original sound. Voyager 1, a spacecraft speeding out of the solar system, travels about two kilometers farther away from the sun during this time frame. A tuning fork pitched to A above middle C vibrates 44 times.
SECOND
A healthy person’s heartbeat lasts about this long. On average, Americans eat 350 slices of pizza during this time. Earth travels 30 kilometers around the sun, while the sun zips 274 kilometers on its trek through the galaxy. It is not quite enough time for moonlight to reach Earth (1.3 seconds). Traditionally the second was the 60th part of the 24th part of a day, but science has given it a more precise definition: it is the duration of 9,192,631,770 cycles of one type of radiation produced by a cesium 133 atom.
MINUTE
The brain of a newborn baby grows one to two milligrams in this time. A shrew’s fluttering heart beats 1,000 times. The average person can speak about 150 words or read about 250 words. When Mars is closest to Earth, sunlight reflected off the Red Planet’s surface reaches us in about four minutes.
HOUR
Reproducing cells generally take about this long to divide into two. One hour and 16 minutes is the average time between eruptions of the Old Faithful geyser in Yellowstone National Park. Light from Pluto arrives at Earth in five hours and 20 minutes.
DAY
For humans, this is perhaps the most natural unit of time, the duration of Earth’s rotation. Currently clocked at 23 hours, 56 minutes and 4.1 seconds, our planet’s rotation is constantly slowing because of gravitational drag from the moon and other influences. The human heart beats about 100,000 times in a day, and the lungs inhale about 11,000 liters of air. In the same amount of time, an infant blue whale adds another 91 kilograms (200 pounds) to its bulk.
YEAR
Earth makes one circuit around the sun and spins on its axis 365.26 times. The mean level of the oceans rises between one and 2.5 millimeters, and North America moves about three centimeters away from Europe. It takes 4.3 years for light from Proxima Centauri, the closest star, to reach Earth—approximately the same amount of time that ocean-surface currents take to circumnavigate the globe.
CENTURY
The moon recedes from Earth by another 3.8 meters. Standard compact discs are expected to degrade in this time. Baby boomers have a one-in-26 chance of living to the age of 100, but giant tortoises can live as long as 177 years. The most advanced recordable CDs may last more than 200 years.
MILLION YEARS
After traveling for a million years, a spaceship moving at the speed of light would not yet be halfway to the Andromeda galaxy (2.3 million light-years away). The most massive stars, blue supergiants that are millions of times brighter than the sun, burn out in about this much time. Because of the movement of Earth’s tectonic plates, Los Angeles will creep about 40 kilometers north-northwest of its present location in a million years.
BILLION YEARS
It took approximately this long for the newly formed Earth to cool, develop oceans, give birth to single-celled life and exchange its carbon dioxide–rich early atmosphere for an oxygen-rich one. Meanwhile the sun orbited four times around the center of the galaxy. Because the universe is 12 billion to 14 billion years old, units of time beyond a billion years aren’t used very often. But cosmologists believe that the universe will probably keep expanding indefinitely, until long after the last star dies (100 trillion years from now) and the last black hole evaporates (10100 years from now). Our future stretches ahead much further than our past trails behind.