Time Travel

Time Travel

We all travel in time. During the last year, I've moved forward one year and
 so have you. Another way to say that is that we travel in time at the rate of 1
 hour per hour.
But the question is, can we travel in time faster or slower than "1 hour per hour"?

The great 20th century scientist Albert Einstein developed a theory called Special Relativity. This theory says that space and time are really aspects of the same thing—space-time. There's a speed limit of 300,000 kilometers per second (or 186,000 miles per second) for anything that travels through space-time, and light always travels the speed limit through empty space. Special Relativity also says that a surprising thing happens when you move through space-time, especially when your speed relative to other objects is close to the speed of light. Time goes slower for you than for the people you left behind. You won't notice this effect until you return to those stationary people. Say you were 15 years old when you left Earth in a spacecraft traveling at about 99.5% of the speed of light (which is much faster than we can achieve now), and celebrated only five birthdays
 during your space voyage.

When you get home at the age of 20, you would find that all your classmates
 were 65 years old, Because time passed more slowly for you, you will have
experienced only five years of life, while your classmates will have experienced
 a full 50 years. Time travel of a sort also occurs for objects in gravitational
fields. Einstein had  another remarkable theory called General Relativity,
which predicts that time passes more slowly for objects in gravitational fields
 (like here on Earth) than for objects far from such fields. So there are all kinds of space and time distortions near black holes, where the gravity can be very intense. In the past few years, some scientists
have used those distortions in space-time to think of possible ways time machines could work. Some like the idea of "worm holes," which may be shortcuts through space-time. This and other ideas are wonderfully interesting, but we don't know at this point whether they are possible for real objects. Still the ideas are based on good, solid science. In all time travel theories allowed by real science, there is no way a traveler can go back in time to before the time machine was built. Actually, scientists and engineers who plan and operate some space missions must account for the time distortions that occur because of both General and Special Relativity. These effects are far too small to matter in most human terms or even over a human lifetime. However, very tiny fractions of a second do matter for the precise work necessary to fly spacecraft throughout the solar system.