By Alan Cooper,2014-07-25 09:15
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    Traveling Through Time

    Imagine being able to travel 200 years into

    the future. Or think about taking a journey far

    back into the past. Time travel has long been a

    dream for many people. But is it just a dream?

    Until recently, everyone thought so. It was fun to ponder,

    scientists said, but it wasnt really possible. Now, some scientists are changing their minds. They say that maybe,

    just maybe, time travel is possible.

     Think about time for minute. What is it, really? You can

    watch the second hand on a clock move around the dial. If you

    watch it long enough, youll see the minute hand move. And if you wait even longer, youll notice that the hour hand also moves. The clock on the wall is one measure of time. But it is

    not the only measure.

     A great scientist named Albert Einstein showed that time has

    many measures. As a young man, Einstein thought a lot about

    light and time. One day he had a thought that no one had ever

    had before. Einstein wondered what a clock would look like if

    he were riding away from it on a beam of light. He guessed that

    the clock would appear to stand still. In other words, time would

stand still!

    Why did Einstein make that guess? Imagine that a clock reads

    exactly 2 P.M. You can see that because light shining off the

    clock shows the position of the hands. The light travels to your

    eye and your brain reads, 2 P.M. A second later, the hand on the clock moves to one second after 2 P.M. Light is still

    bouncing off the clock. So another beam of light carries a new

    message to your eye. Now your brain reads, one second after

    2:00 P.M. Beams of light travel so fast that you can read each

    message instantly. But imagine riding on the beam of light that

    carries the2 P.M. message. The other beam of light---the one

    carrying the message one second after 2 P.M.---would never

    catch up with you. So for you, the clock would always read 2


     Using experiments, Einstein proved his guess was right. He

    confirmed that speed slows down the passage of time. In that

    sense, everyone has already done at least a tiny bit of time

    traveling. You have done it each time you have ridden in a car or

    plane. Such time travel, however, is far too slight to notice.

     Now think like Einstein. Suppose you go very, very fast. In

    fact, you go almost the speed of light. (Light travels at about

    186,000 miles per second! Thats more than a million times

faster than a jet plane!) At that speed, youd find that time really

    does slow down. Message from other beams of light would

    catch up with you, but only after a long chase.

     Because speed slows down time, you would age slowly as

    you zip through space. Meanwhile, back on Earth, time would pass it always does. While youd be getting five years older,

    people on Earth might be getting 205 years older. If you return to Earth after you five years, you would find you had traveled 200 years into the future!

     Such time travel is not feasible yet. The fastest spaceships can go only a few thousand miles an hour. We havent found a way

    to go any faster. In theory, however, there is a way we could do it. We could use what is called a black hole. A black hole, if it really exists, is a gigantic star that has used up all its fuel. It has collapsed into itself, becoming very small. The gravitational pull from a black hole would be immense. It would be so great, in fact, that everything passing by it--- even light beams---would get sucked in. Things would get trapped in a wild funnel that looks a bit like a tornado. The winds in this funnel would be close to the speed of light.

     If a spaceship could approach the funnel at just the right angle, the black hole might act as a slingshot. It could whip the

    spaceship around and send it flying back out through space at a super-high speed. (Of course, the pilot would have to be very careful. He or she could not fly too close to the black hole. Otherwise, the whole spaceship would get pulled in and

    compressed to less than the size of a grain of sand!)

     Now imagine that you want to travel back into the past. That would be even harder to do. You would have to catch up with light beams carrying messages from long ago. To do that, youd

    have to travel faster than the speed of light. That is not possible. Nothing can go faster than a light beam. Still, some scientists think theres away to get around that problem. They suggest

    taking a shortcut through space. That way, a traveler light be able to catch up with some old beams of light. Scientists have a picture in their minds of what this kind of shortcut would look like. They have even given it a name. They call it a wormhole.”

    No one knows if wormholes exist. But of they do, travelers might someday use them to jump back in time.

     Before you get too excited about traveling to the past, think about some of the questions it would raise. Suppose you traveled back to April 14, 1865. That was the day President Abraham Lincoln was shot. Could you prevent the assassination? Suppose you did. How would that change the course of

American history?

     Scientists often put the questions in personal terms. Suppose you time-travel back 60 years, to the days when your grandmother is a young woman. Your mother has not yet been born. If you somehow stop your grandmother from meeting your grandfather, where does that leave you? Now your mother wont

    be born. Does this mean you will cease to exist?

     People love to fantasize about time travel. The question is this can we really find a way to do it? Will it remain just a dream, carried out only in books or at the movies? Or will we someday be able to fly off into the future and back into the past? Only time will tell.

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