In Search of Time: Journeys Along a Curious Dimension - Couverture rigide

Falk, Dan

Couverture rigide

ISBN 10 : 1906367191 ISBN 13 : 9781906367190

Editeur : National Maritime Museum, 2009

Synopsis

`Time’s definition is elusive but Dan Falk is keen to track it down. In this thoroughly readable, broad-sweeping and thought-provoking book, Falk surveys humanity’s attempts to record and understand time, and poses some fascinating questions.’ – New Scientist `Falk seamlessly combines science with literary and philosophical observations… and digresses to fascinating topics like root notions of past and future, the vagaries of memory and the behavior of birds at breakfast time.’ – Publishers Weekly (starred review) `What is time?’Falk considers cultural attitudes towards time from prehistory to the present, recounts different philosophers’ explanations of the phenomenon of time, outlines the history of time-keeping, and examines centuries of scientific thought on the topic, from Newton through Einstein to the Big Bang and beyond. He speaks with anthropologists and historians about our deep desire to track time’s cycles, asks psychologists and neuroscientists about the mysteries of memory, and quizzes physicists about the beginning and end of time – not to mention the latest theories about time travel and the paradoxes it seems to entail. What can ancient sites such as the`passage tomb’ in Newgrange, Ireland, tell us about our ancestors’ understanding of time? Why is the medieval clock at the Salisbury Cathedral so special? How do human differ from other species in our perception of the past and future? What implications do Einstein’s theories have for the possibility of time travel? Is time an illusion? From ancient observatories to nanoseconds, from the layers of geological`deep time’ to atomic clocks, Falk offers an engaging, thought-provoking account of how humans have come to understand time over the centuries and how that understanding continues to evolve today, not only in the fields of physics, astronomy, philosophy and psychology but also in everyday life.

A propos du livre

Extrait

HEAVENLY CLOCKWORK
Time's natural cycles
 
The first grand discovery was time, the landscape of experience.
– Daniel Boorstin, The Discoverers
 
The city of Drogheda, just half an hour north of Dublin by Irish Rail's InterCity service, isn't at the top of most tourists' Ireland itineraries. Even Lonely Planet, which praises the surrounding counties for their historical and cultural wealth, describes this small coastal city as "charmless." As my taxi heads west, however, the view steadily improves, with Drogheda's industrial clutter giving way to the rolling hills and green valleys of County Meath. And just a few kilometers farther inland lies one of the most important prehistoric monuments in all of Europe – the "passage tomb" of Newgrange.
 
Most visitors to Newgrange approach from the south side of the Boyne, through the main visitor center, but for my early morning appointment I have to come from the north side of the famous river, past Newgrange Farm, where the sound of birds and cowbells fills the morning air. As the taxi rounds the last bend in the road, the monument itself – a shallow, circular, grass-covered mound some eighty meters across and a dozen meters high – comes into view. The outer walls are lined with blocks of white quartz that glitter in the sunlight. I'm met by Claire Tuffy of the Office of Public Works, which manages the site, and together we climb the gentle hill leading to the tomb's main entrance.
 
The structure, Tuffy explains, dates from around 3100 B.C. – making it five centuries older than the Great Pyramid at Giza in Egypt, and a full thousand years older than the "trilithons" at the center of Stonehenge. The Neolithic people who lived in Ireland at that time would have been farmers, tending grain crops and herding livestock. The Boyne – Tuffy nods toward the river, half-hidden by trees and low hills – was their highway. They had likely been farming the land for a thousand years before construction at Newgrange began. "Their tools were stone and wood – no metal," Tuffy points out. The quartz was transported from what is now County Wicklow, some eighty kilometers away. One can only imagine the Herculean effort required to move, shape, and lift the nearly two thousand stones used to construct the monument.
 
We pass the richly decorated sandstone blocks that mark the entrance, and approach the iron gate that now protects the interior. Tuffy unlocks it and we step inside, ducking our heads because of the low ceiling. Though circular on the outside, the interior of the tomb is long and narrow, cutting deep into the center of the mound. We make our way cautiously toward the rear of the chamber. Soon the entrance is little more than a tiny square of light in the distance behind us. Without the electric lights installed overhead every few meters, it would be pitch black. It is also eerily quiet. For the pair of bats that have built their nest here, it is no doubt the perfect home.
 
The tomb stretches twenty-five meters in length but rarely spans more than a meter across. At the far end are three small alcoves that branch off from the main passage, giving the tomb an elongated cruciform design. Though known to the modern Irish since the seventeenth century, the site wasn't properly excavated until the 1960s, when archeologist Michael O'Kelly and his team discovered the cremated bones of at least five individuals, on basin-like stones in the alcoves at the rear of the tomb. Workers also uncovered intriguing Neolithic artwork. Several of the stones are decorated with geometrical patterns; the most complex is a trio of overlapping spirals at the very back of the tomb.
 
As we stand in the rear chamber, Tuffy shines her flashlight at the layers of cobbled stones that arch overhead. "That roof has not been restored, and it is still perfectly watertight after five thousand years of Irish weather," she says. Why would Neolithic farmers have gone to that much trouble to protect the bones of the dead from a little water? Perhaps the spirits of the ancestors were thought to live on, she speculates. And while today is sunny, Tuffy reminds me with a smile that her country has been known to have the occasional spot of rain. "Maybe it's every Irish person's idea of heaven, to be dry for ever and ever," she muses.
 
But the most intriguing feature of Newgrange is neither its walls, nor its roof, nor its artwork. It is not what one sees at any one place, but rather what one sees at a particular time. Every winter, on the morning of the shortest day of the year – the winter solstice – sunlight streams through a small opening above the main entrance, known as the "roof box," illuminating the back of the tomb. This seemingly innocuous event – a sliver of sunlight briefly creeping into a dusky burial chamber in the dead of winter – is what makes Newgrange unique. These weathered stones allow us to glimpse, however dimly, into the minds of those who first considered the matter of time.
 
 
The Sun in the Cave
Were the roof box and passage constructed along a slightly different angle, the solstice event would not happen. Could it be a coincidence, a chance alignment? Almost certainly not, says astronomer Tom Ray of the Dublin Institute for Advanced Studies, who investigated the geometry of Newgrange in the 1980s. "As an astronomer, as a mathematician, I'm looking at the statistics and saying, the chances of this being an accident are very, very small," Ray told me when I visited him in his Dublin office. The solar alignment "was their intention." Andrew Powell, writing in a prominent archeological journal a few years ago, reached the same conclusion: "There can be no doubt that this was an integral feature of the tomb's design."
 
The modern name Newgrange comes from the Gaelic Uaimh na Greine, "The Cave of the Sun." In fact, even before those first excavations in the Sixties, there were local legends about sunlight entering the cave at a particular time of year. O'Kelly wondered if it might involve the winter solstice, as such alignments are well known in later Neolithic monuments. So he camped out in the cave overnight, waking up early on the morning of December 21, 1969, to see for himself (and, just to be sure, he repeated the experiment the following year). Ray, telling me the story, is mildly amused. "From the point of view of an astronomer, you don't need to actually do that," he says. "You could have just done a bit of surveying, and that would have told you the answer. So we have this sort of romantic image of Michael O'Kelly stuck in the back of the chamber, on the shortest day of the year, waiting for the sun to rise. And lo and behold, when it did, he realized that the light came into the main chamber of Newgrange." As O'Kelly noted in his journal that morning:
 
At exactly 8:54 hours gmt the top edge of the ball of the sun appeared above the local horizon and at 8:58 hours, the first pencil of direct sunlight shone through the roof-box and along the passage to reach the tomb chamber floor as far as the front edge of the basin stone in the end recess.
 
But our view today is not precisely the same as it would have been five thousand years ago. For one thing, Ray explains, the earth's axis wobbles periodically over thousands of years. The phenomenon is related to the precession of the earth's rotation axis: as the earth spins, the axis itself gradually revolves with respect to the solar system, in a cycle that lasts about 26,000 years. The related wobble – astronomers call it "nutation" – causes a periodic change in the tilt of the axis. Today, the axis is tilted 23.5 degrees; at the time Newgrange was built, the tilt was slightly greater – about 24 degrees. The upshot of that small shift, Ray explains, is that the shortest day of the year was a little bit shorter back then, and the longest day was a little bit longer. That, in turn, affects the time of sunrise and sunset. Today, on the solstice – as O'Kelly noticed – several minutes pass between sunrise and the first penetration of sunlight into the rear of the tomb. Five thousand years ago, however, it would have been bang on. "You would have captured the sun just as it rose," says Ray.
 
The solstice sunrise at Newgrange is still a remarkable event. Every year, thousands of people take part in a lottery for the privilege of a morning visit to the tomb in the week of December 21. Because the main passageway is angled upward, those first rays of sunlight don't hit the back wall; instead, as O'Kelly observed, they hit the ground a few meters short of the rear of the tomb. It is that first strike of sunlight inside the tomb that those lucky visitors watch for. "Nobody takes their eye off the ground," says Tuffy, who has probably witnessed the event more often than anyone else in recent years. "You lose your sense of how much time has passed. And despite the fact that everybody is watching the floor, people inevitably miss the first beam of light." Soon the beam is about the length and width of a pencil, Tuffy says. "And then very quickly it gets longer and wider, and it moves down the floor." By the time it reaches the middle of the chamber – just a few minutes later – it's nearly twenty centimeters wide, and surprisingly intense. "It's a lovely, warm color," she says. "And then the whole room is so bright you can see right up as far as the capstone. You can see the faces of all the people gathered in the room."
 
What does the solar alignment tell us about the Neolithic people who moved so many massive stones into place, in such a precise way, to build such a structure? We can imagine that the builders of Newgrange – as one could say of people in any farming community today – took an intense interest in the passing of the seasons and the motions of the heavenly bodies, particularly the sun and moon. In those days, before the glare of streetlights a...

Revue de presse

Dan Falk is a riveting writer: his latest book is almost unputdown-able ... Time is a mysterious commodity: we gain, spend, save and lose it. But everyone should make enough time to read In Search of Time. --Martin J. Rees, Astronomer Royal and author of Just Six Numbers and Our Final Hour

Time has intrigued philosophers and scientists from Aristotle to Newton, from Zeno to Hawking. Falk has fun in his search for time, discussing it with researchers who make some educated guesses ... Falk s tour of time is worth a few hours of our own. --The Times

Falk deals entertainingly with the history of man s attempts to measure time, from the sun rising over Neolithic monuments to today s super-accurate atomic clocks. He discusses cultural differences ... and he describes the difficulties our ancestors faced in making sense of months and years that contain days and fractions of days ... An accessible and entertaining introduction to what is, perhaps, the deepest and most intractable secret of the universe. --Financial Times

Détails de l'édition

• Éditeur: National Maritime Museum
• Date d'édition: 2009
• Langue: anglais
• ISBN 10: 1906367191
• ISBN 13: 9781906367190
• Reliure: Relié
• Nombre de pages: 352
• Coordonnées du fabricant: non disponible
• Personne responsable: non disponible