COULD YOU EVER BUILD A TIME MACHINE? 3. Shortcuts to the Future
Figure 1. A journey into the future might reveal some amazing advances such as this giant space colony.
Figure 2. In a dried-out condition, a tardigrade, or "water bear," can extend its life to as much as 60 times its normal life span.
Figure 3. The famous physicist Albert Einstein demonstrates one of his scientific theories.
Figure 4. 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.
Figure 5. Cosmic-ray shower.
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 space.
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 (see Figure 2). 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!
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 (see Figure 3). Einstein found that strange things happen to an object as it reaches very high speeds.
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! (see Figure 4)
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!
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.
Time-Traveling Particles
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 (see Figure 5).
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 below 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
light (relative to Earth) |
Amount by which time is slowed (relative to Earth) |
| 0 | 1.000 |
| 10 | 1.005 |
| 20 | 1.021 |
| 30 | 1.048 |
| 40 | 1.091 |
| 50 | 1.155 |
| 60 | 1.250 |
| 70 | 1.400 |
| 80 | 1.667 |
| 90 | 2.294 |
| 95 | 3.202 |
| 99 | 7.089 |
| 99.9 | 22.361 |
| 99.999 | 223.607 |
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.
