Worlds of David Darling > Children's
Encyclopedia of Science > Could You Ever Build a Time Machine? > 1.
COULD YOU EVER BUILD A TIME MACHINE? Tweet
a book in the Could You Ever? series by David Darling
1. About Time Tweet
The results of this experiment are clear. They show that while you have freedom to move around in space, you have no control at all over your motion through time. Despite all your efforts, your watch will not appear to have gained or lost any time as compared with the clock that did not move.
Yet, the more you think about it, the stranger that seems. After all, people today can quickly cover huge distances in jet aircraft. They can explore both on and below the Earth's surface. Astronauts have even traveled as far away as the Moon. We can move about in space almost as we please. Yet no ne has ever managed to jump even one second forward into the future or back into the past.
We are all forced, it seems, to move through time at the same rate and in the same direction. It is as if we were passengers together on a train. All we can see is the ever-changing scenery of the present moment through the side windows. The view through the driver's window at what is to come, and through the back window from the caboose at what has already gone by, is blocked from us. Or is it?
Gone But Not Forgotten
This talent for remembering and passing on knowledge is one of the reasons human beings have been able to make such remarkable progress. Throughout human history, people have made many great discoveries, inventions, and works of art. The past has been preserved through books, paintings, sculptures, and music.
But more recently, humans have developed other, more accurate ways of bringing the past back to life. Since the middle of the nineteenth century, cameras have allowed events to be captured on film. Through photographs, we can see how things really were at a particular place and time.
Movie cameras have given us even more power to recreate the past. Since their invention around the start of the last century, they have recorded many of the world's greatest events. Today, from World War I battles to astronauts on the Moon, these can be viewed over and over again. People who had not even been born at the time can see glimpses of the world from more than 50 years ago.
Not only sights, but also sounds can now be replayed with complete accuracy. Following the invention of the phonograph in 1877, our ability to record and replay sounds has developed at a rapid pace. Today, with hand-held TV sound cameras and video recorders, we can capture, in precise detail, sounds and moving pictures from the everyday world. For example, people now routinely record the birth of their children or family Christmas celebrations on DVD. Then, years later, the disk can be shown on a television set or computer. In a sense, the TV screen becomes a window in the past.
The Past All Around
The sounds you are hearing at this moment come from a thousandth of second in the past for every foot they traveled to reach your ears. You do not hear them instantly because sound moves through air at about 1,000 feet per second. During a thunderstorm, for instance, the rumble from a lightning flash three miles away will not reach you for 15 seconds.
What is true of sound is also true of light. But light travels a million times faster than sound, or 186,282 miles per second. This is such an enormous speed that the light from everyday objects reaches us almost immediately. But as we look at things that are farther and farther away, it takes longer and longer for the light from them to travel to our eyes.
Light from the Sun, for example, takes slightly more than eight minutes to arrive at the Earth. Light from the brightest star in the night sky, Sirius, requires more than eight years to make the journey across a distance of about 25 trillion miles. This means that we are seeing Sirius not as it is now, but as it was more than eight years ago! In the case of most stars in the night sky, their light has taken hundreds or even thousands of years to reach our eyes.
The fact is, we see nothing as it really is. Everything you look at, even your on hand or the writing on this page, is as it was in the past. What is more, the farther away you look, the farther back in time you see. Here on Earth this effect is so tiny that we are never aware of it. But for astronomers studying the Universe, the effect is very important, indeed. By gazing into space through giant telescopes, astronomers can look far back in time. If they look at the most distant objects yet discovered, they can see the Universe as it was about 15 billion years ago, not long after it formed.
With the help of modern inventions, the, we can store sounds and pictures of events, and later replay them. By gazing more deeply into space, we can look farther and farther back into time. This means that devices such as cameras, video recorders, and telescopes are all "time machines" of a sort. And yet, they are useless for actually traveling into the past or for giving us any side of what the future might be like.
To explore the past in person, or to see into the future, would be much more interesting. But it might also lead to unusual and quite baffling problems.