Worlds of David Darling > Children's
Encyclopedia of Science > Could You Ever Build a Time Machine? > 3.
Shortcuts to the Future
COULD YOU EVER BUILD A TIME MACHINE?
a book in the Could You Ever? series by David Darling
3. Shortcuts to the Future
Within the last 100 years, the world has changed beyond all recognition.
To someone from the year 1900, jet aircraft, television sets, computers,
microwave ovens, and many other modern devices would seem like magic. A
century ago, people traveled slowly by horse-drawn carriage. Today, they
glide along freeways in cars at a mile a minute. People can use mobile phones
to talk to other people anywhere on Earth. They can watch events in another
country as they happen via signals transmitted by a satellite far out in
|A journey into the future might reveal some
amazing advances such as this giant space colony
Given that change has come so quickly, imagine what things may be like in
the year 2100 or beyond. Perhaps, by then, people will have colonized other
planets around the Sun. Or there may be computers that are more intelligent
than human beings. The possibilities are endless, and we can scarcely begin
to imagine them all.
Zooming into the future sounds like something only Marty McFly could do
in his time-traveling sports car. Yet it is not as far-fetched as it seems.
The Long, Deep Sleep
Along with the rest of the Universe, we are all traveling into the future
every instant of our lives. In time, we become older and die, which limits
how far forward we can go. From the moment we are born, we have the chance
to see, on average, about 80 years into the future. Some people are fortunate
and live to be more than 100. But beyond that our only chance of survival
is to slow or stop the normal processes of aging.
Scientists already know that some very small animals can live much longer
than usual by becoming dried out. Tardigrades, for instance, are small,
squat creatures less than a twentieth of an inch in length with four pairs
of legs. Normally, they live in films and pools of fresh water. But if the
water dries up, so do the tardigrades. Humans would die if they lost more
than one-fifth of the water in their bodies. Tardigrades, however, can lose
99 percent of their body-water and still survive. In this parched condition,
they can live for long periods of time. A tardigrade that is repeatedly
dried out and revived can lengthen its life from a normal span of less than
a year to about 60 years!
|In a dried-out condition, a tardigrade, or
"water bear," can extend its life to as much as 60 times its normal
Another way to extend life is to place it in a deep freeze. Researchers,
for instance, have revived bacteria that became trapped in antarctic ice
thousands of years ago. But would the same methods of lengthening life work
with a person?
Drying out people and preserving them like tardigrades woudn'l not work.
Humans die if they lose much body water. But the idea of freezing living
people and reviving them at a later date is more reasonable. The main problem
is that water expands when it freezes. Water is a major ingredient in all
the cells, or tiny living units, of our bodies. If frozen, this water would
tend to burst and kill every cell.
Despite such problems, several American companies already offer the unusual
service of freezing dead bodies. The bodies are frozen so that in the future,
doctors may have the opportunity to treat the conditions that caused the
people to die. For now, reviving frozen human beings, whether dead or alive,
is not possible. But in the years to come, new advances may help us to make
this technique work.
There is a better chance that we shall learn how to extend our lives using
special medicines or replacement body parts. Perhaps within your lifetime,
human beings will live much longer than they do today.
Time and Speed
Another way to travel into the future was discovered by the great German-boen
American physicist Albert Einstein in the early 1900s. Einstein found that
strange things happen to an object as it reaches very high speeds.
|The famous physicist Albert Einstein demonstrates
one of his scientific theories
The key to understanding these unusual effects is the speed of light. Light
moves at 186,282 miles per second in empty space – the highest possible
speed in the Universe. But, as Einstein first pointed out, the speed of
light in empty space is always measured to be 186,282 miles per
second. Its measured speed stays the same whether a person or an object
is moving toward the source of light or away from it!
This seems not to make sense compared to other scientific measurements.
For example, if you measured the speed of an oncoming car while driving
down the freeway, the closing speed would be equal to your own speed plus
that of the approaching vehicle. But that doesn't work in the case of light.
Your own speed does not affect in the slightest the speed at which the light
appears to be moving.
Starting from this simple, surprising fact, Einstein went on to produce
an amazing theory. He realized that if the speed of light always remains
the same, then other basic quantities such as time and length must vary.
Previously, scientists had believed that time always flows at the same rate
everywhere in the Universe. But Einstein proved that this is not true. In
fact, for objects moving at high speed, time slows down!
|To the driver of Car A, Car B seems to be approaching
at 100 miles per hour. But the pilot of a high-speed spaceship would
measure the speed of light to be the same whether the spaceship was
moving toward the source of light, or away from it.
According to the math behind Einstein's theory, the effects of time slowing
down only become noticeable near to the speed of light. So far, no one has
traveled as fast as one-thousandth of light-speed. Even the astronauts who
went to the Moon reached a top speed of just 25,000 miles per hour. This
is equal to seven miles per second, or about 26,000 times slower than light!
The clocks aboard the Apollo spacecraft did run slightly slower than clocks
on Earth. Still, the astronauts aged only about one-thousandth of a second
less than if they had not gone on the journey.
In years to come, though, it is likely that humans will build much faster
spacecraft. Indeed, they will have to if they hope to cross the vast distances
to even the nearest stars within a crew's lifetime. Then, the effects predicted
by Einstein will become much more important.
It will be many years before spacecraft are built that can travel
close to the speed of light. But Einstein's predictions about the
strange slowing down of time at high speeds can already be tested
on much smaller objects.
Every day, the Earth is showered with tiny particles that come from
far away in space. These particles, which are of various types, are
known as cosmic rays. When cosmic rays strike the Earth's upper atmosphere,
they give rise to other particles known as mesons.
Mesons have a lifetime of about two-millionths of a second. During
that instant in time, they could normally cover about 2,000 feet.
This is far short of the distance they would have to travel to reach
the Earth's surface from the edge of space where they are created.
Yet mesons, formed from collisions with cosmic rays, are detected
on the ground! How can this be?
Mesons travel so fast that time slows down for them. This means they
have a much longer lifetime than normal. For a meson moving at near
light-speed, the 25 miles it must travel to reach the Earth's surface
seems like only a few hundred yards. The rate by which the meson's
own time is slowed down, scientists have found, exactly matches the
amount predicted by Einstein's theory.
Lost in Time
The table to the right shows how much time would slow down for objects moving
at various speeds. Traveling at 10 percent of the speed of light, or 18,628
miles per second, a spacecraft's time would not be slowed down by much.
But at 90 percent of the speed of light, or 167,654 miles per second, time
changes greatly. The crew members aboard such a spacecraft would age by
less than half the amount than if they had stayed behind on Earth.
|Einstein time-slowing effect
|Percentage of the speed of
(relative to Earth)
|Amount by which time is slowed
(relative to Earth)
Imagine the situation, though, of a starship that can reach 99.999 percent
of light speed. Traveling at this rate, the starship's crew would live 1
year for every 223 years that went by on Earth. Suppose the voyage lasted
10 years as measured by clocks on board the starship. Then when the crew
returned to Earth, they would find themselves 2,230 years in the future!
While they had been away, the world would have changed beyond their wildest
dreams. It would be as if a group of ancient Greeks had been suddenly transported
into the early twenty-first century.
Yet who would want to make such a journey? Imagine that you could leap hundreds,
thousands, or even millions of years into the future to see what fantastic
developments had taken place. It might sound exciting. But time-traveling
in a high-speed spaceship would allow you to go only one way. You would
have to leave your homeland and time far behind, and you would be a stranger
in a place far, far away. There would be no way to return to Earth. Yet
there is one other way of traveling through time that might not have this
problem. In theory, it would permit two-way voyages – both into the
future and the past. But it would also mean flying into one of the strangest
and most terrifying objects scientists have ever imagined.