Читать книгу Time, Twilight, and Eternity - Thom Rock - Страница 14

We say the existence of eternity cannot be proven, that it makes no logical sense. But the same can be said of the measurement of something we’ve agreed to call, for lack of a better word, time. There was a time when we simply looked to the sky to guide us—when the planet spun, tilted on its axis just so, and there was evening and there was day—and that was enough. Or, on a more practical, corporeal level, we looked to our stomachs to tell us, for example, when it was time to eat. We didn’t have a name for it back then, but the suprachiasmatic nucleus and preoptic areas in the part of our brains known as the hypothalamus told us when it was time to sleep or time to rise and shine.

Then we decided those markers needed further delineation and we made up hours.

Then minutes.

Then seconds.

Now we tick time off in fractions thereof: microseconds, and nanoseconds.21 Our digitized, computerized, speed-mad world streams by 24/7 at warp speed—or, at least at information transfer rates of so many kilobits and megabits and gigabits and terabits every second.

The base unit of time in the International System of Units as well as other systems of measurement, we usually think of a second as the simple division of a minute into sixty equal measures; the minute being a previous sexagesimal division of the hour. While seconds have been used to measure and calculate time at least since the time of al-Bīrūnī, the preeminent eleventh-century Persian mathematician and astronomer, it wasn’t until much later that the second was formally defined as 1/86,400th of a day.

That definition of a second didn’t last very long.

Now the scientific standard of time is measured in atomic terms, by the steady frequency of emitted photons: the antiquated second has been updated to “the duration of 9,192,631,770 beats of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium 133 atom at rest at a temperature of 0 on the Kelvin thermodynamic scale.”

No wonder we’re out of breath.

Rush Hour

Cesium-beam atomic clocks can measure time accurately to within trillionths of a second. Or, in context, the time needed for a beam of light travelling at 186,000 miles per second to travel less than the distance equivalent to the thickness of a sheet of paper, a page of a book. When it comes to time, accuracy is absolutely important. Think about the air traffic controller and so many planes speeding through space to the same runway . . . or any navigation, be it by air, land, or sea, or even outer space. Timing is everything. A network of atomic timekeepers and other chronographic instruments circles our planet, constantly monitored and synchronized via signals and satellites circling in turn in the space above the planet into near-perfect, super-precise lockstep with each other. All this circling data is continuously collected and analyzed at the International Bureau of Weights and Measures in Sèvres, France day and night, internationally agreed upon as Coordinated Universal Time—as the time—then spun back out into the non-stop spinning world and dials of the watches on our wrists to complete the circle.

Still, the planet spins, tilted on its axis just so, and there is evening and there is day. Twenty-four hours, a pirouette: an arbitrary measure of time we agree to obey.

Except we do not all leap gracefully through space at the same speed: circumference and latitude join us in the dance. Because the earth makes one complete revolution on its axis every twenty-four hours (what we have come to know as a “day”) we can calculate the surface speed of the spinning earth as the division of the planet’s circumference by the same number of hours. We don’t all spin at the same tempo, though, because the circumference of the earth decreases latitude by latitude the closer one gets to either the North or South Pole. New Orleans is a bit more up tempo than Fairbanks, Alaska; revelers in Rio dance faster than their counterparts Down Under. At the equator the circumference of the earth is 40, 070 kilometers, which translates to a surface speed of around 1,670 kilometers, or 1,040 miles, per hour. Some thirty-four degrees north of the equator, Los Angeles, California spins at about 860 miles per hour, about the same speed as Tokushima, Japan or Peshawar, Pakistan. Where I live—just about mid-way between the equator and the North Pole—the planet’s rotational speed is slower than that, although considerably faster than, say, Qaanaaq, Greenland, or Kirovsk, Russia—or any other human settlement above the Arctic Circle (where any given day may have as many as twenty-four hours of darkness or daylight depending on the season.)

The trouble is, one complete planetary pirouette in the galactic ballet that is the exquisitely choreographed dance of our twirling orbit around the sun—and by which we’ve decided to measure time and construct a day—doesn’t always equal a day exactly all the time and everywhere. The earth’s rotational rate is neither static nor a reliable measure of time. In this age of high-precision timekeeping, navigators and astronomers look elsewhere more and more frequently for the tick-tock accuracy upon which we all depend. Astronomical observation over the last two centuries has revealed that the mean solar day—the time it takes for the planet to make one complete revolution on its axis—is slowly but measurably lengthening. Thus, even the measures of time we have come to know as weeks, months, and years are no longer completely accurate.

That is, if we’re all even talking about the same year, following the same calendar.

Which we’re not.

Year after Year

While some of us (religious, or not) follow the standard Gregorian calendar, that record of time measures years in relation to the presumed birth of Jesus Christ, a reckoning of time introduced by Pope Gregory XIII in AD 1582, (AD being an abbreviation of anno Domini—or, year of our Lord—a notation of historical time first assigned in the sixth century.) To be fair, Gregory hardly invented the system all on his own. He and the rest of the world had inherited earlier—and far from accurate—versions from both Christian and Roman pontiffs and emperors alike (who, in turn, had inherited even earlier calendars from their predecessors; ancient artifacts suggest that even our Paleolithic ancestors created rudimentary calendars more than six millennia ago based on the changes of the moon.) But by the time Gregory was pope the inaccuracies of earlier calendars were wreaking havoc; they were running either too fast or too slow compared to the true solar year or the actual seasons of the planet. The trouble was that so many timekeepers had conveniently rounded up or down (or even manipulated for political reasons) the number of days it took for the ball of dirt we call home to circle the sun. Some calculated the number to be 364; others 365. The more attentive thought the year to be 365 ¼ days. The actual length of the year is closer to 365 days, 5 hours, 48 minutes and 45 seconds—although even that precise counting of time is neither steady nor static: on average, due to the gradual slowing of the earth’s rotation, the year decreases in time about half a second every century.

But seconds can turn into minutes; minutes can become hours, become days. By the time Gregory issued his papal bull “officially” correcting what time it was, the calendar had drifted off course by nearly ten days. Easter was no longer eastering when it was supposed to. (Not to mention Passover was passing over at the wrong time, and the Ramadan fast was running slow.) With a stroke of the pen, the days between October fifth and October fourteenth were eliminated from the year 1582. Widely adopted in Catholic countries, the Gregorian calendar took some time to catch on. Protestants, especially, were suspicious, not least because it meant forfeiting nearly ten days of their lives (and wages) forever. The Pope’s calendar was not officially adopted in Britain until sometime in the eighteenth century. Japan waited until the century after that, and Orthodox Russians and China held out until the early- to mid-1900s. The Eastern Orthodox Church still does not follow the Gregorian calendar but one based on a system first devised by the ancient Egyptians.

Previous to the Pope’s decree a year had been noted AUC, as ab urbe condita—or, from the (symbolic) founding of the city and empire of Rome, in what was then the dominant day-keeper of the time—the Julian calendar—a measurement of time introduced by Julius Caesar, itself an updated iteration of an earlier Roman calendar supposedly introduced by none other than the mythic King Romulus and which consisted of only ten months and lasted only 304 days. While the use of BC, or “before Christ,” and AD to identify years eventually superseded the Roman idea of what came before and what came after, those markers have now been widely replaced by the less Christocentric terms BCE and CE, or “before the common era” and “common era” respectively. Though there have been plenty of movements to embrace other demarcations of time throughout history. Some timekeepers, for example, lobbied for the observation of time since the “Era of the Passion,” with year one dating back to AD 33, the presumed date of Christ’s crucifixion and resurrection. Mussolini imposed a new calendar, marked Era Fascista, to introduce and document his reign of power. The French Revolution ushered in its own method of keeping track of time, the Calendar of Reason, which lasted just over a decade—at which point the new emperor, Napoleon Bonaparte, abolished it.