primordial
adj. existing at the beginning of time

pulse
n. 脉搏

reckon
v. to calculate

refinement
n. improvement

regardless of
(infml) without being affected by different situations

relativity
n. theory of ～:爱因斯坦的相对论

reverse
v. to go backwards

rhythm
n. a regular repeated pattern of movements or sounds 节奏

riddle
n. a mystery; sth. one cannot understand

Roman
n. 罗马人

satellite
n. a machine that is sent into space and goes around the Earth used for radio, television or communication 卫星

signal
v. to express or indicate time 显示或表示（时间）

Sir
n. （放在姓名前）爵士

slave
n. a person completely dominated by another thing or person 奴隶

split
v. to divide into two or more parts

Sumerian
n. people in ancient Euphrates in Asia（古代幼发拉底地区）

technological
adj. related to technology 工艺的

tension
n. (a feeling of) nervous anxiety, worry, or pressure

theoretical
adj. based on theory

theorist
n. = theoretician; someone who develops ideas within a particular subject that explain why particular things happen or are true 理论家

therefore
adv. for that reason; as a result

tick
v. ～ away: to pass by (said of time)

timekeeping
n. the recording of time

timepiece
n. a clock or watch 计时器

track
v. to follow the movement

ultimately
adv. in the end; after everything or everyone else has been done or considered

uniform
adj. being all the same in all its parts or among all its members

unified
adj. 统一的

variable
n. sth. that may be different in different situations so that you cannot be sure what will happen 可变因数

voyager
n. sb. who often makes long and dangerous journeys; Voyager (U.S.)探索者号（飞船）

waterwheel
n. a wheel turned by a flow of water, used to work machinery

width
n. size from side to side 宽度

Proper Names

Allan
艾伦

Landes
兰德斯

Ehret
埃雷特

Feynman
范曼

Gregory XIII
格雷戈里十三世

Galileo Galilei
伽利略·伽利莱伊

Gernot Winkler
格诺特·温克勒

Isaac Newton
艾萨克·牛顿

Willard Libby
威拉德·利比

Text A

The Riddle of Time

John Boslough

Read the text once for the main idea. Do not refer to the notes, dictionaries or the glossary yet.

We run our lives by clocks and calendars... but what is time?

"We physicists work with time every day," said Nobel Prize winner Richard P. Feynman, "but don't ask me what it is. It's just too difficult to think about."
Throughout much of history time was looked upon as a flow like a river. Even for Sir Isaac Newton, the flow of time was uniform. But with Albert Einstein's theory of relativity, time was seen as a dimension — like height and width — giving a unified picture of events in time and space. "We have given more attention to measuring time than to any other variable in nature," says Gernot Winkler of the U.S. Naval Observatory in Washington, D.C. "But time remains a riddle that exists only in our minds."
Devising accurate calendars and clocks to measure the flow of time has, through history, proved to be an elusive, lengthy intellectual pursuit. The Sumerians divided the year into 360 days, then named 12 lunar months of 30 days each. The Egyptians extended the year by five days. Later changes by the Romans, plus refinements by Pope Gregory XIII in 1582, gave us today's Gregorian calendar, accurate to a day in every 3323 years.
Early societies also broke the day into smaller units. The sun, arcing overhead daily, was undoubtedly the first timepiece, followed perhaps by the shadow of a stick stuck in the ground — a crude sundial.
In the 11th century a Chinese scholar named Su Sung invented a huge device that was among the first mechanical water clocks. More than 30 feet high, powered by a waterwheel, his clock signaled the hours with gongs, bells and drums.
It was in the West, however, that the mechanical clock achieved its greatest glory. One of the earliest was built for an English monastery in the 13th century.
In 16th-century Italy, a young medical student named Galileo Galilei is said to have spied a newly lighted lamp swinging in the cathedral at Pisa. Timing it with his pulse, he found that each swing took the same amount of time, regardless of the distance traveled. He had discovered the pendulum. But seven decades passed before a Dutch scientist built the first pendulum clock, starting the era of precision timekeeping.
The Western idea that past, present and future are arranged in a straight line — that time does not repeat — seems to have grown out of the Christian tradition in which Christ's birth took on special meaning because it was unique and therefore unrepeatable.
In human terms, even as you watch a second tick away, it's gone. But our technological world needs the precise time. A navigator at sea or in the air, plotting location by satellite, relies on a time signal accurate to within a single millionth of a second. Spacecraft like Voyager 2 are guided by radio commands timed to billionths of a second. And physicists tracking motion inside an atom reckon in trillionths of a second.
Atomic clocks at some 50 timekeeping stations around the world from Washington to Paris to Moscow allow this remarkable splitting of seconds. Since the 1940s, scientists have known that the electrons of atoms oscillate with a rhythm so regular that — like a pendulum — they could be used to tell time. First built in 1948, these clocks generally use atoms of cesium, a silvery white metal, and are accurate to within a few nanoseconds a day.
But does this give us a clue to what time is? Not really, says David Allan, a time theorist. "Clocks are very limited devices." He points out that the past does not exist except in our memory. "Nor the future, except in our expectations of it," he says. "The most a clock gives is the time an instant ago. Time is our own invention."
Nature, too, has its clocks. In 1947 American chemist Willard Libby found a natural timekeeper in everything that lived during the past 50,000 years: the carbon atom, which decays at a known rate. By determining its level of carbon-14, scientists can tell the age of an Egyptian mummy or of charcoal from an ancient Indian home.
Astronomers have gazed even farther back in time. By looking at light from a faraway galaxy, they are actually seeing the galaxy as it was billions of years ago. The rate at which these galaxies are flying away from one another tells scientists the date when all the matter in the universe set out on its journey.
"We were able to show that the matter in the universe must have been infinitely compressed about 15 billion years ago," says theoretical physicist Stephen Hawking of the University of Cambridge in England. And before that? "Time as we measure it simply did not exist."
But human time — the perception of our bodies and minds — has origins deep in a primordial past long before a set of gears told us when to go to bed. The body's dominant time cycle is called the circadian rhythm, the control for which is believed to lie in the brain, above the roof of the mouth. For most of us a normal circadian cycle is 25 hours, give or take 15 minutes.
Why not 24? "Being slightly out of step with nature may have created a kind of tension necessary for survival," suggests Charles Ehret, president of General Chronobionics near Chicago.
A few body-clock watchers believe we may also tick to an array of weekly cycles. They are thought to regulate changes in body chemicals, the response of the immune system, and a cyclic rise and fall of heartbeat and blood circulation. Such rhythms, some scientists believe, may help explain the seven-day week as a unit of time — the only calendar measure that does not trace its origins to astronomy.
Ehret is certain that if you abuse your powerful internal rhythms, you are in for trouble. Monday-morning blues, sleep disorders and even depression can result from the mismatch between the clock on the wall and the ones in the body.
So the human body is as much a part of the clockwork universe as any timepiece we ever built. But what of the other questions we all have about time: can we travel through it, or can it be reversed? Who has not wished to turn back clock or calendar — to erase mistakes, to return as a child with adult wisdom, and to chat with Shakespeare? But scientists say that though the laws of physics may not forbid time travel, all observed arrows of time go in only one direction.
Whatever time is, we humans have internalized it so powerfully that it has taken on a meaning all its own. We run our lives by numbers on clocks and calendars that we ourselves have created. Have we become slaves to the clock?
David Landes, a historian of timekeeping at Harvard University, thinks not. "The clock let individuals know what time belonged to their employers and what time was their own. Workers are now actually freer than ever before. Without the clock, and now the watch, there is no modern world. It is the difference between a complex, intricately coordinated society and a primitive one only vaguely aware of time's possibilities."
"We ultimately are still in control of how we use time and how it affects us." More than anything else time is what we make of it.