Worlds of David Darling > Children's
Encyclopedia of Science > Could You Ever Build a Time Machine? > 2.
It's Yesterday Once More
COULD YOU EVER BUILD A TIME MACHINE?
a book in the Could You Ever? series by David Darling
2. It's Yesterday Once More
Any sensible explorer will prepare well before setting out on an adventure
into the unknown. So, before looking at how real time travel might be achieved,
we should consider the risks and problems that might be involved. Like Marty
McFly in Back to the Future, we might find that trips into the
past can affect the future in unexpected ways.
|The time-traveling car in
Back to the Future
Imagine, for instance, you have just invented a vehicle that can transport
you back to any date you wish. You dial a time 160 years ago, sit back in
the pilot's seat, and pull back the starting lever. There is a blurred motion
outside the cabin window. In just a few seconds, as measured by your own
watch, you have hurtled back more than a century and a half.
Unfortunately, your time machine has landed on and squashed one of your
ancestors! Had the accident not happened, this person would have become
the father of your great-great-grandfather. But now history has been changed.
A whole branch of you family has been wiped out. Worst of all, without that
part of your family tree, you will not be born! Yet, here you are standing
outside your time machine in the 1840s. How can this be?
Hurriedly climbing back into your machine, you reset the time-dial to April
14, 1865. The destination you choose is Ford's Theater, Washington, D.C.
You arrive just minutes before John Wilkes Booth is due to slip into the
private box of Abraham Lincoln and his wife to shoot the president. At least
now you have a chance to make up for your earlier mistake. Quickly, you
warn the authroities of the assassination attempt on Lincoln. Because of
your action, the gunman is arrested, and Lincoln is not killed. But what
will be the affect on world history?
Changing the Past
Even sending back objects rather than people into the past could cause some
strange problems. In one short story, a professor invents a machine that
can transport a small brass cube back through time. He tells his friend
that at exactly three o'clock, he will place a cube on the time machine's
platform and send it back five minutes into the past.
"Therefore," says the professor, "the cube should, at five minutes before
three, vanish from my hand and appear on the platform." And, sure enough,
"See!" exclaims the professor. "Five minutes before I shall place it there,
it is there!"
But now comes the interesting part of the story. One of the professor's
friends has a question. What would happen, now that the box has made its
journey back though time, if the professor fails to put the box on the time
machine at three o'clock? Fascinated, the professor decides to find out.
It proves to be a terrible mistake. In the story, at exactly three o'clock,
the professor, his friends, and the whole Universe – except for the
brass box – disappear!
When we start talking about time travel into the past, we encounter many
logical problems such as the ones just mentioned. For this reason, some
scientists believe that going back in time is not possible. Others argue
that, if a time traveler did go into the past, it would cause a split in
time. One branch of time would carry on as before. The other, with the time
traveler in it, would contain differences because of the time traveler's
According to this theory, if you went back to try to save Lincoln's life,
you would create two different futures. In one, Lincoln would be shot and
killed. In another, containing you and your time machine, he would live
on. Look at the diagram above to understand how this might work.
Where Are All the Time Machines?
One of the strongest arguments that has been made against time travel could
be called "the case of the missing time machines." In other words, if in
the future time machines are invented, then why has no one seen any of them?
|Photo of a UFO
If time travel did become possible, it seems likely that thousands of people
would want to take advantage of it. Time cruises might be offered to the
age when wooly mammoths and saber-toothed tigers still roamed the Earth.
Other tourists might be more interested in seeing ancient Rome, or Columbus
setting sail for the New World. Surely, if time machines from the future
had visited key moments in history, including our own time, someone would
have spotted them by now?
Well, perhaps they have. It is possible, for instance, that some UFOs, or
Unidentified Flying Objects, are time machines from the future. Of course,
the chance of this being true is very, very small indeed. It is also possible
that we cannot see these future time travelers or their machines. They may
choose to keep themselves invisible to avoid changing history. In spite
of the problems that it seems to raise, time travel may be taking place.
Seeing Into the Future
Can some people see events before they actually happen? Is there a connection
between the present and the future?
A large number of men, women, and children claim to have experienced precognition.
This often takes the form of a dream in which a disaster is seen taking
place, such as the crash of an aircraft. Later, the accident my occur just
as in the dream. As with all such claims, it is very difficult to supply
A second type of experience, which many of us have from time to time, is
called deja vu. This is a sensation, lasting just a few seconds, that what
is happening has occurred in exactly the same way before. Could it be that
a future situation has been seen in a dream, forgotten, and then remembered
only when it actually takes place? No one knows.
Finally, there is the mystery of premonition. This is the feeling many people
say they have that something, perhaps very sad, happy, or important, is
about to take place. More often than not, it involves members of the same
family, and especially identical twins.
If precognition, deja vu, and premonition are real, rather than imagined,
then scientists have a difficult problem. They must explain why human beings
appear to be able to see into the future. Is there some "sixth sense," as
yet undetected, that can reach back and forth in time? Or do future events
send ripples into the past that we can pick up, especially when we are asleep?
Much more research is needed to find the answers.
But whether or not we can see future events, it is possible that someday
people will be able to travel into the future. There are at least two ways,
in theory, that human beings could use to journey far into the world of