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So is time travel possible?

General Relativity

                                  TO KNOW ABOUT TIME TRAVEL .FIRST YOU NEED TO HAVE SOME KNOWLEDGE ABOUT  GENERAL RELATIVITY.

 According to general relativity, mass curves spacetime mass there is somewhere, the more spacetime will be curved there. Now, what is spacetime, and what does it mean for it to be curved? Well, according to general relativity, space and time are fundamentally connected to each other, and they may together be thought of as forming a unified object called “spacetime.” They’re like the two sides of a coin — they’re fundamentally different from each other, but it’s impossible to think of them separately. In a world where this is no gravity, we say that spacetime is not curved; it is flat. This is the world of special relativity. There’s a precise mathematical meaning, of course, to this whole business of spacetime being curved — it’s related to what I discussed in Lecture Notes 2 with the Universe having some kind of a shape — but for these notes, all you need to know is that spacetime can have the property of being “curved.” Now, it turns out that time operates very differently in curved spacetime than in flat spacetime. 

 For example, in curved spacetime, there is the effect of gravitational time dilation. This is the effect whereby clocks tick slower near massive bodies than far away from them. In other words, the greater the gravity, the slower a clock will tick; therefore, the more curved spacetime 1This is barring speculative ideas such as tachyons — hypothetical particles that can travel faster than light. In principle, a tachyon would necessarily travel backward in time. However, tachyons have never been detected and there’s absolutely no reason whatsoever to believe that they exist. Sorry, Prot. 7 is, the slower a clock will tick. Thus, a clock on the surface of the Earth will run slower than a clock 10 miles above the Earth’s surface, because the clock sitting on the surface is in a region where the gravity is greater and therefore the spacetime is more curved.2 A small leap of logic then shows that gravitational time dilation presents an alternative method for traveling into the future! Suppose you sit near a very massive object, where spacetime is very curved. Then (depending on how massive the object is), while a very short amount of time may elapse for you, a very long amount of time may elapse for someone far away from the very massive object. As a result, you’ll have effectively traveled into the future!

 Time Travel to the Past

                                     So now we have a second method of traveling into the future. What about time travel to the past? Well, I should mention from the start that nobody in the world knows if it’s possible to travel back in time. But people have thought about it over the years, and they’ve come up with some methods that might work. . . but might not work. In these notes, I’ll briefly discuss one of them. General relativity, being the bizarre theory it is, allows for the existence of very strange objects called “wormholes” when the geometry of spacetime is sufficiently funky. A wormhole is simply a path between two places in spacetime. But it isn’t any old path between two places — it’s a shortcut between them. For example, consider the star Sirius, which is approximately 54 trillion miles away. If you traveled at nearly the speed of light, it would ordinarily take you about 9 years to reach it. But if the Earth and Sirius were connected by a wormhole, then it’s possible for you to travel through the wormhole — which may only be 10 feet long — and thereby reach the Andromeda Galaxy in a matter of seconds!

I am confident time travel into the future is possible, but we would need to develop some very advanced technology to do it. We could travel 10,000 years into the future and age only 1 year during that journey. However, such a trip would consume an extraordinary amount of energy. Time travel to the past is more difficult. We do not understand the science as well.

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.


Find out how one NASA mission is doing some very clever space-time experiments to test Einstein's theory of relativity using the International Space Station.